[PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Chao Peng]

This patch series implements KVM guest private memory for confidential
computing scenarios like Intel TDX[1]. If a TDX host accesses
TDX-protected guest memory, machine check can happen which can further
crash the running host system, this is terrible for multi-tenant
configurations. The host accesses include those from KVM userspace like
QEMU. This series addresses KVM userspace induced crash by introducing
new mm and KVM interfaces so KVM userspace can still manage guest memory
via a fd-based approach, but it can never access the guest memory
content.

The patch series touches both core mm and KVM code. I appreciate
Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
reviews are always welcome.
  - 01: mm change, target for mm tree
  - 02-09: KVM change, target for KVM tree

Given KVM is the only current user for the mm part, I have chatted with
Paolo and he is OK to merge the mm change through KVM tree, but
reviewed-by/acked-by is still expected from the mm people.

The patches have been verified with Intel TDX environment, but Vishal
has done an excellent work on the selftests[4] which are dedicated for
this series, making it possible to test this series without innovative
hardware and fancy steps of building a VM environment. See Test section
below for more info.


Introduction
============
KVM userspace being able to crash the host is horrible. Under current
KVM architecture, all guest memory is inherently accessible from KVM
userspace and is exposed to the mentioned crash issue. The goal of this
series is to provide a solution to align mm and KVM, on a userspace
inaccessible approach of exposing guest memory. 

Normally, KVM populates secondary page table (e.g. EPT) by using a host
virtual address (hva) from core mm page table (e.g. x86 userspace page
table). This requires guest memory being mmaped into KVM userspace, but
this is also the source where the mentioned crash issue can happen. In
theory, apart from those 'shared' memory for device emulation etc, guest
memory doesn't have to be mmaped into KVM userspace.

This series introduces fd-based guest memory which will not be mmaped
into KVM userspace. KVM populates secondary page table by using a
fd/offset pair backed by a memory file system. The fd can be created
from a supported memory filesystem like tmpfs/hugetlbfs and KVM can
directly interact with them with newly introduced in-kernel interface,
therefore remove the KVM userspace from the path of accessing/mmaping
the guest memory. 

Kirill had a patch [2] to address the same issue in a different way. It
tracks guest encrypted memory at the 'struct page' level and relies on
HWPOISON to reject the userspace access. The patch has been discussed in
several online and offline threads and resulted in a design document [3]
which is also the original proposal for this series. Later this patch
series evolved as more comments received in community but the major
concepts in [3] still hold true so recommend reading.

The patch series may also be useful for other usages, for example, pure
software approach may use it to harden itself against unintentional
access to guest memory. This series is designed with these usages in
mind but doesn't have code directly support them and extension might be
needed.


mm change
=========
Introduces a new memfd_restricted system call which can create memory
file that is restricted from userspace access via normal MMU operations
like read(), write() or mmap() etc and the only way to use it is
passing it to a third kernel module like KVM and relying on it to
access the fd through the newly added restrictedmem kernel interface.
The restrictedmem interface bridges the memory file subsystems
(tmpfs/hugetlbfs etc) and their users (KVM in this case) and provides
bi-directional communication between them. 


KVM change
==========
Extends the KVM memslot to provide guest private (encrypted) memory from
a fd. With this extension, a single memslot can maintain both private
memory through private fd (restricted_fd/restricted_offset) and shared
(unencrypted) memory through userspace mmaped host virtual address
(userspace_addr). For a particular guest page, the corresponding page in
KVM memslot can be only either private or shared and only one of the
shared/private parts of the memslot is visible to guest. For how this
new extension is used in QEMU, please refer to kvm_set_phys_mem() in
below TDX-enabled QEMU repo.

Introduces new KVM_EXIT_MEMORY_FAULT exit to allow userspace to get the
chance on decision-making for shared <-> private memory conversion. The
exit can be an implicit conversion in KVM page fault handler or an
explicit conversion from guest OS.

Introduces new KVM ioctl KVM_SET_MEMORY_ATTRIBUTES to maintain whether a
page is private or shared. This ioctl allows userspace to convert a page
between private <-> shared. The data maintained tells the truth whether
a guest page is private or shared and this information will be used in
KVM page fault handler to decide whether the private or the shared part
of the memslot is visible to guest.


Test
====
Ran two kinds of tests:
  - Selftests [4] from Vishal and VM boot tests in non-TDX environment
    Code also in below repo: https://github.com/chao-p/linux/tree/privmem-v10

  - Functional tests in TDX capable environment
    Tested the new functionalities in TDX environment. Code repos:
    Linux: https://github.com/chao-p/linux/tree/privmem-v10-tdx
    QEMU: https://github.com/chao-p/qemu/tree/privmem-v10

    An example QEMU command line for TDX test:
    -object tdx-guest,id=tdx,debug=off,sept-ve-disable=off \
    -machine confidential-guest-support=tdx \
    -object memory-backend-memfd-private,id=ram1,size=${mem} \
    -machine memory-backend=ram1


TODO
====
  - Page accounting and limiting for encrypted memory
  - hugetlbfs support


Changelog
=========
v10:
  - mm: hook up restricted_memfd to memory failure and route it to
    kernel users through .error() callback.
  - mm: call invalidate() notifier only for FALLOC_FL_PUNCH_HOLE, i.e.
    not for allocation.
  - KVM: introduce new ioctl KVM_SET_MEMORY_ATTRIBUTES for memory
    conversion instead of reusing KVM_MEMORY_ENCRYPT_{UN,}REG_REGION.
  - KVM: refine gfn-based mmu_notifier_retry() mechanism.
  - KVM: improve lpage_info updating code.
  - KVM: fix the bug in private memory handling that a private fault may
    fall into a non-private memslot.
  - KVM: handle memory machine check error for fd-based memory.
v9:
  - mm: move inaccessible memfd into separated syscall.
  - mm: return page instead of pfn_t for inaccessible_get_pfn and remove
    inaccessible_put_pfn.
  - KVM: rename inaccessible/private to restricted and CONFIG change to
    make the code friendly to pKVM.
  - KVM: add invalidate_begin/end pair to fix race contention and revise
    the lock protection for invalidation path.
  - KVM: optimize setting lpage_info for > 2M level by direct accessing
    lower level's result.
  - KVM: avoid load xarray in kvm_mmu_max_mapping_level() and instead let
    the caller to pass in is_private.
  - KVM: API doc improvement.
v8:
  - mm: redesign mm part by introducing a shim layer(inaccessible_memfd)
    in memfd to avoid touch the memory file systems directly.
  - mm: exclude F_SEAL_AUTO_ALLOCATE as it is for shared memory and
    cause confusion in this series, will send out separately.
  - doc: exclude the man page change, it's not kernel patch and will
    send out separately.
  - KVM: adapt to use the new mm inaccessible_memfd interface.
  - KVM: update lpage_info when setting mem_attr_array to support
    large page.
  - KVM: change from xa_store_range to xa_store for mem_attr_array due
    to xa_store_range overrides all entries which is not intended
    behavior for us.
  - KVM: refine the mmu_invalidate_retry_gfn mechanism for private page.
  - KVM: reorganize KVM_MEMORY_ENCRYPT_{UN,}REG_REGION and private page
    handling code suggested by Sean.
v7:
  - mm: introduce F_SEAL_AUTO_ALLOCATE to avoid double allocation.
  - KVM: use KVM_MEMORY_ENCRYPT_{UN,}REG_REGION to record
    private/shared info.
  - KVM: use similar sync mechanism between zap/page fault paths as
    mmu_notifier for memfile_notifier based invalidation.
v6:
  - mm: introduce MEMFILE_F_* flags into memfile_node to allow checking
    feature consistence among all memfile_notifier users and get rid of
    internal flags like SHM_F_INACCESSIBLE.
  - mm: make pfn_ops callbacks being members of memfile_backing_store
    and then refer to it directly in memfile_notifier.
  - mm: remove backing store unregister.
  - mm: remove RLIMIT_MEMLOCK based memory accounting and limiting.
  - KVM: reorganize patch sequence for page fault handling and private
    memory enabling.
v5:
  - Add man page for MFD_INACCESSIBLE flag and improve KVM API do for
    the new memslot extensions.
  - mm: introduce memfile_{un}register_backing_store to allow memory
    backing store to register/unregister it from memfile_notifier.
  - mm: remove F_SEAL_INACCESSIBLE, use in-kernel flag
    (SHM_F_INACCESSIBLE for shmem) instead. 
  - mm: add memory accounting and limiting (RLIMIT_MEMLOCK based) for
    MFD_INACCESSIBLE memory.
  - KVM: remove the overlap check for mapping the same file+offset into
    multiple gfns due to perf consideration, warned in document.
v4:
  - mm: rename memfd_ops to memfile_notifier and separate it from
    memfd.c to standalone memfile-notifier.c.
  - KVM: move pfn_ops to per-memslot scope from per-vm scope and allow
    registering multiple memslots to the same memory backing store.
  - KVM: add a 'kvm' reference in memslot so that we can recover kvm in
    memfile_notifier handlers.
  - KVM: add 'private_' prefix for the new fields in memslot.
  - KVM: reshape the 'type' to 'flag' for kvm_memory_exit
v3:
  - Remove 'RFC' prefix.
  - Fix race condition between memfile_notifier handlers and kvm destroy.
  - mm: introduce MFD_INACCESSIBLE flag for memfd_create() to force
    setting F_SEAL_INACCESSIBLE when the fd is created.
  - KVM: add the shared part of the memslot back to make private/shared
    pages live in one memslot.

Reference
=========
[1] Intel TDX:
https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html
[2] Kirill's implementation:
https://lore.kernel.org/all/20210416154106.23721-1-kirill.shutemov@linux.intel.com/T/ 
[3] Original design proposal:
https://lore.kernel.org/all/20210824005248.200037-1-seanjc@google.com/  
[4] Selftest:
https://lore.kernel.org/all/20221111014244.1714148-1-vannapurve@google.com/


Chao Peng (8):
  KVM: Introduce per-page memory attributes
  KVM: Extend the memslot to support fd-based private memory
  KVM: Add KVM_EXIT_MEMORY_FAULT exit
  KVM: Use gfn instead of hva for mmu_notifier_retry
  KVM: Unmap existing mappings when change the memory attributes
  KVM: Update lpage info when private/shared memory are mixed
  KVM: Handle page fault for private memory
  KVM: Enable and expose KVM_MEM_PRIVATE

Kirill A. Shutemov (1):
  mm: Introduce memfd_restricted system call to create restricted user
    memory

 Documentation/virt/kvm/api.rst         | 125 ++++++-
 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 arch/x86/include/asm/kvm_host.h        |   9 +
 arch/x86/kvm/Kconfig                   |   3 +
 arch/x86/kvm/mmu/mmu.c                 | 205 ++++++++++-
 arch/x86/kvm/mmu/mmu_internal.h        |  14 +-
 arch/x86/kvm/mmu/mmutrace.h            |   1 +
 arch/x86/kvm/mmu/tdp_mmu.c             |   2 +-
 arch/x86/kvm/x86.c                     |  17 +-
 include/linux/kvm_host.h               | 103 +++++-
 include/linux/restrictedmem.h          |  71 ++++
 include/linux/syscalls.h               |   1 +
 include/uapi/asm-generic/unistd.h      |   5 +-
 include/uapi/linux/kvm.h               |  53 +++
 include/uapi/linux/magic.h             |   1 +
 kernel/sys_ni.c                        |   3 +
 mm/Kconfig                             |   4 +
 mm/Makefile                            |   1 +
 mm/memory-failure.c                    |   3 +
 mm/restrictedmem.c                     | 318 +++++++++++++++++
 virt/kvm/Kconfig                       |   6 +
 virt/kvm/kvm_main.c                    | 469 +++++++++++++++++++++----
 23 files changed, 1323 insertions(+), 93 deletions(-)
 create mode 100644 include/linux/restrictedmem.h
 create mode 100644 mm/restrictedmem.c


base-commit: df0bb47baa95aad133820b149851d5b94cbc6790
-- 
2.25.1

[PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

Introduce 'memfd_restricted' system call with the ability to create
memory areas that are restricted from userspace access through ordinary
MMU operations (e.g. read/write/mmap). The memory content is expected to
be used through the new in-kernel interface by a third kernel module.

memfd_restricted() is useful for scenarios where a file descriptor(fd)
can be used as an interface into mm but want to restrict userspace's
ability on the fd. Initially it is designed to provide protections for
KVM encrypted guest memory.

Normally KVM uses memfd memory via mmapping the memfd into KVM userspace
(e.g. QEMU) and then using the mmaped virtual address to setup the
mapping in the KVM secondary page table (e.g. EPT). With confidential
computing technologies like Intel TDX, the memfd memory may be encrypted
with special key for special software domain (e.g. KVM guest) and is not
expected to be directly accessed by userspace. Precisely, userspace
access to such encrypted memory may lead to host crash so should be
prevented.

memfd_restricted() provides semantics required for KVM guest encrypted
memory support that a fd created with memfd_restricted() is going to be
used as the source of guest memory in confidential computing environment
and KVM can directly interact with core-mm without the need to expose
the memoy content into KVM userspace.

KVM userspace is still in charge of the lifecycle of the fd. It should
pass the created fd to KVM. KVM uses the new restrictedmem_get_page() to
obtain the physical memory page and then uses it to populate the KVM
secondary page table entries.

The userspace restricted memfd can be fallocate-ed or hole-punched
from userspace. When hole-punched, KVM can get notified through
invalidate_start/invalidate_end() callbacks, KVM then gets chance to
remove any mapped entries of the range in the secondary page tables.

Machine check can happen for memory pages in the restricted memfd,
instead of routing this directly to userspace, we call the error()
callback that KVM registered. KVM then gets chance to handle it
correctly.

memfd_restricted() itself is implemented as a shim layer on top of real
memory file systems (currently tmpfs). Pages in restrictedmem are marked
as unmovable and unevictable, this is required for current confidential
usage. But in future this might be changed.

By default memfd_restricted() prevents userspace read, write and mmap.
By defining new bit in the 'flags', it can be extended to support other
restricted semantics in the future.

The system call is currently wired up for x86 arch.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 include/linux/restrictedmem.h          |  71 ++++++
 include/linux/syscalls.h               |   1 +
 include/uapi/asm-generic/unistd.h      |   5 +-
 include/uapi/linux/magic.h             |   1 +
 kernel/sys_ni.c                        |   3 +
 mm/Kconfig                             |   4 +
 mm/Makefile                            |   1 +
 mm/memory-failure.c                    |   3 +
 mm/restrictedmem.c                     | 318 +++++++++++++++++++++++++
 11 files changed, 408 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/restrictedmem.h
 create mode 100644 mm/restrictedmem.c

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 320480a8db4f..dc70ba90247e 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -455,3 +455,4 @@
 448	i386	process_mrelease	sys_process_mrelease
 449	i386	futex_waitv		sys_futex_waitv
 450	i386	set_mempolicy_home_node		sys_set_mempolicy_home_node
+451	i386	memfd_restricted	sys_memfd_restricted
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index c84d12608cd2..06516abc8318 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -372,6 +372,7 @@
 448	common	process_mrelease	sys_process_mrelease
 449	common	futex_waitv		sys_futex_waitv
 450	common	set_mempolicy_home_node	sys_set_mempolicy_home_node
+451	common	memfd_restricted	sys_memfd_restricted
 
 #
 # Due to a historical design error, certain syscalls are numbered differently
diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
new file mode 100644
index 000000000000..c2700c5daa43
--- /dev/null
+++ b/include/linux/restrictedmem.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _LINUX_RESTRICTEDMEM_H
+
+#include <linux/file.h>
+#include <linux/magic.h>
+#include <linux/pfn_t.h>
+
+struct restrictedmem_notifier;
+
+struct restrictedmem_notifier_ops {
+	void (*invalidate_start)(struct restrictedmem_notifier *notifier,
+				 pgoff_t start, pgoff_t end);
+	void (*invalidate_end)(struct restrictedmem_notifier *notifier,
+			       pgoff_t start, pgoff_t end);
+	void (*error)(struct restrictedmem_notifier *notifier,
+			       pgoff_t start, pgoff_t end);
+};
+
+struct restrictedmem_notifier {
+	struct list_head list;
+	const struct restrictedmem_notifier_ops *ops;
+};
+
+#ifdef CONFIG_RESTRICTEDMEM
+
+void restrictedmem_register_notifier(struct file *file,
+				     struct restrictedmem_notifier *notifier);
+void restrictedmem_unregister_notifier(struct file *file,
+				       struct restrictedmem_notifier *notifier);
+
+int restrictedmem_get_page(struct file *file, pgoff_t offset,
+			   struct page **pagep, int *order);
+
+static inline bool file_is_restrictedmem(struct file *file)
+{
+	return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC;
+}
+
+void restrictedmem_error_page(struct page *page, struct address_space *mapping);
+
+#else
+
+static inline void restrictedmem_register_notifier(struct file *file,
+				     struct restrictedmem_notifier *notifier)
+{
+}
+
+static inline void restrictedmem_unregister_notifier(struct file *file,
+				       struct restrictedmem_notifier *notifier)
+{
+}
+
+static inline int restrictedmem_get_page(struct file *file, pgoff_t offset,
+					 struct page **pagep, int *order)
+{
+	return -1;
+}
+
+static inline bool file_is_restrictedmem(struct file *file)
+{
+	return false;
+}
+
+static inline void restrictedmem_error_page(struct page *page,
+					    struct address_space *mapping)
+{
+}
+
+#endif /* CONFIG_RESTRICTEDMEM */
+
+#endif /* _LINUX_RESTRICTEDMEM_H */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a34b0f9a9972..f9e9e0c820c5 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1056,6 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
 asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
 					    unsigned long home_node,
 					    unsigned long flags);
+asmlinkage long sys_memfd_restricted(unsigned int flags);
 
 /*
  * Architecture-specific system calls
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 45fa180cc56a..e93cd35e46d0 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
 #define __NR_set_mempolicy_home_node 450
 __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
 
+#define __NR_memfd_restricted 451
+__SYSCALL(__NR_memfd_restricted, sys_memfd_restricted)
+
 #undef __NR_syscalls
-#define __NR_syscalls 451
+#define __NR_syscalls 452
 
 /*
  * 32 bit systems traditionally used different
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index 6325d1d0e90f..8aa38324b90a 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -101,5 +101,6 @@
 #define DMA_BUF_MAGIC		0x444d4142	/* "DMAB" */
 #define DEVMEM_MAGIC		0x454d444d	/* "DMEM" */
 #define SECRETMEM_MAGIC		0x5345434d	/* "SECM" */
+#define RESTRICTEDMEM_MAGIC	0x5245534d	/* "RESM" */
 
 #endif /* __LINUX_MAGIC_H__ */
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 860b2dcf3ac4..7c4a32cbd2e7 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -360,6 +360,9 @@ COND_SYSCALL(pkey_free);
 /* memfd_secret */
 COND_SYSCALL(memfd_secret);
 
+/* memfd_restricted */
+COND_SYSCALL(memfd_restricted);
+
 /*
  * Architecture specific weak syscall entries.
  */
diff --git a/mm/Kconfig b/mm/Kconfig
index 57e1d8c5b505..06b0e1d6b8c1 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1076,6 +1076,10 @@ config IO_MAPPING
 config SECRETMEM
 	def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
 
+config RESTRICTEDMEM
+	bool
+	depends on TMPFS
+
 config ANON_VMA_NAME
 	bool "Anonymous VMA name support"
 	depends on PROC_FS && ADVISE_SYSCALLS && MMU
diff --git a/mm/Makefile b/mm/Makefile
index 8e105e5b3e29..bcbb0edf9ba1 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -121,6 +121,7 @@ obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
 obj-$(CONFIG_PAGE_TABLE_CHECK) += page_table_check.o
 obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
 obj-$(CONFIG_SECRETMEM) += secretmem.o
+obj-$(CONFIG_RESTRICTEDMEM) += restrictedmem.o
 obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o
 obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
 obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 145bb561ddb3..f91b444e471e 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -62,6 +62,7 @@
 #include <linux/page-isolation.h>
 #include <linux/pagewalk.h>
 #include <linux/shmem_fs.h>
+#include <linux/restrictedmem.h>
 #include "swap.h"
 #include "internal.h"
 #include "ras/ras_event.h"
@@ -940,6 +941,8 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
 		goto out;
 	}
 
+	restrictedmem_error_page(p, mapping);
+
 	/*
 	 * The shmem page is kept in page cache instead of truncating
 	 * so is expected to have an extra refcount after error-handling.
diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
new file mode 100644
index 000000000000..56953c204e5c
--- /dev/null
+++ b/mm/restrictedmem.c
@@ -0,0 +1,318 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "linux/sbitmap.h"
+#include <linux/pagemap.h>
+#include <linux/pseudo_fs.h>
+#include <linux/shmem_fs.h>
+#include <linux/syscalls.h>
+#include <uapi/linux/falloc.h>
+#include <uapi/linux/magic.h>
+#include <linux/restrictedmem.h>
+
+struct restrictedmem_data {
+	struct mutex lock;
+	struct file *memfd;
+	struct list_head notifiers;
+};
+
+static void restrictedmem_invalidate_start(struct restrictedmem_data *data,
+					   pgoff_t start, pgoff_t end)
+{
+	struct restrictedmem_notifier *notifier;
+
+	mutex_lock(&data->lock);
+	list_for_each_entry(notifier, &data->notifiers, list) {
+		notifier->ops->invalidate_start(notifier, start, end);
+	}
+	mutex_unlock(&data->lock);
+}
+
+static void restrictedmem_invalidate_end(struct restrictedmem_data *data,
+					 pgoff_t start, pgoff_t end)
+{
+	struct restrictedmem_notifier *notifier;
+
+	mutex_lock(&data->lock);
+	list_for_each_entry(notifier, &data->notifiers, list) {
+		notifier->ops->invalidate_end(notifier, start, end);
+	}
+	mutex_unlock(&data->lock);
+}
+
+static void restrictedmem_notifier_error(struct restrictedmem_data *data,
+					 pgoff_t start, pgoff_t end)
+{
+	struct restrictedmem_notifier *notifier;
+
+	mutex_lock(&data->lock);
+	list_for_each_entry(notifier, &data->notifiers, list) {
+		notifier->ops->error(notifier, start, end);
+	}
+	mutex_unlock(&data->lock);
+}
+
+static int restrictedmem_release(struct inode *inode, struct file *file)
+{
+	struct restrictedmem_data *data = inode->i_mapping->private_data;
+
+	fput(data->memfd);
+	kfree(data);
+	return 0;
+}
+
+static long restrictedmem_punch_hole(struct restrictedmem_data *data, int mode,
+				     loff_t offset, loff_t len)
+{
+	int ret;
+	pgoff_t start, end;
+	struct file *memfd = data->memfd;
+
+	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
+		return -EINVAL;
+
+	start = offset >> PAGE_SHIFT;
+	end = (offset + len) >> PAGE_SHIFT;
+
+	restrictedmem_invalidate_start(data, start, end);
+	ret = memfd->f_op->fallocate(memfd, mode, offset, len);
+	restrictedmem_invalidate_end(data, start, end);
+
+	return ret;
+}
+
+static long restrictedmem_fallocate(struct file *file, int mode,
+				    loff_t offset, loff_t len)
+{
+	struct restrictedmem_data *data = file->f_mapping->private_data;
+	struct file *memfd = data->memfd;
+
+	if (mode & FALLOC_FL_PUNCH_HOLE)
+		return restrictedmem_punch_hole(data, mode, offset, len);
+
+	return memfd->f_op->fallocate(memfd, mode, offset, len);
+}
+
+static const struct file_operations restrictedmem_fops = {
+	.release = restrictedmem_release,
+	.fallocate = restrictedmem_fallocate,
+};
+
+static int restrictedmem_getattr(struct user_namespace *mnt_userns,
+				 const struct path *path, struct kstat *stat,
+				 u32 request_mask, unsigned int query_flags)
+{
+	struct inode *inode = d_inode(path->dentry);
+	struct restrictedmem_data *data = inode->i_mapping->private_data;
+	struct file *memfd = data->memfd;
+
+	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
+					     request_mask, query_flags);
+}
+
+static int restrictedmem_setattr(struct user_namespace *mnt_userns,
+				 struct dentry *dentry, struct iattr *attr)
+{
+	struct inode *inode = d_inode(dentry);
+	struct restrictedmem_data *data = inode->i_mapping->private_data;
+	struct file *memfd = data->memfd;
+	int ret;
+
+	if (attr->ia_valid & ATTR_SIZE) {
+		if (memfd->f_inode->i_size)
+			return -EPERM;
+
+		if (!PAGE_ALIGNED(attr->ia_size))
+			return -EINVAL;
+	}
+
+	ret = memfd->f_inode->i_op->setattr(mnt_userns,
+					    file_dentry(memfd), attr);
+	return ret;
+}
+
+static const struct inode_operations restrictedmem_iops = {
+	.getattr = restrictedmem_getattr,
+	.setattr = restrictedmem_setattr,
+};
+
+static int restrictedmem_init_fs_context(struct fs_context *fc)
+{
+	if (!init_pseudo(fc, RESTRICTEDMEM_MAGIC))
+		return -ENOMEM;
+
+	fc->s_iflags |= SB_I_NOEXEC;
+	return 0;
+}
+
+static struct file_system_type restrictedmem_fs = {
+	.owner		= THIS_MODULE,
+	.name		= "memfd:restrictedmem",
+	.init_fs_context = restrictedmem_init_fs_context,
+	.kill_sb	= kill_anon_super,
+};
+
+static struct vfsmount *restrictedmem_mnt;
+
+static __init int restrictedmem_init(void)
+{
+	restrictedmem_mnt = kern_mount(&restrictedmem_fs);
+	if (IS_ERR(restrictedmem_mnt))
+		return PTR_ERR(restrictedmem_mnt);
+	return 0;
+}
+fs_initcall(restrictedmem_init);
+
+static struct file *restrictedmem_file_create(struct file *memfd)
+{
+	struct restrictedmem_data *data;
+	struct address_space *mapping;
+	struct inode *inode;
+	struct file *file;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return ERR_PTR(-ENOMEM);
+
+	data->memfd = memfd;
+	mutex_init(&data->lock);
+	INIT_LIST_HEAD(&data->notifiers);
+
+	inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
+	if (IS_ERR(inode)) {
+		kfree(data);
+		return ERR_CAST(inode);
+	}
+
+	inode->i_mode |= S_IFREG;
+	inode->i_op = &restrictedmem_iops;
+	inode->i_mapping->private_data = data;
+
+	file = alloc_file_pseudo(inode, restrictedmem_mnt,
+				 "restrictedmem", O_RDWR,
+				 &restrictedmem_fops);
+	if (IS_ERR(file)) {
+		iput(inode);
+		kfree(data);
+		return ERR_CAST(file);
+	}
+
+	file->f_flags |= O_LARGEFILE;
+
+	/*
+	 * These pages are currently unmovable so don't place them into movable
+	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
+	 */
+	mapping = memfd->f_mapping;
+	mapping_set_unevictable(mapping);
+	mapping_set_gfp_mask(mapping,
+			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
+
+	return file;
+}
+
+SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
+{
+	struct file *file, *restricted_file;
+	int fd, err;
+
+	if (flags)
+		return -EINVAL;
+
+	fd = get_unused_fd_flags(0);
+	if (fd < 0)
+		return fd;
+
+	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
+	if (IS_ERR(file)) {
+		err = PTR_ERR(file);
+		goto err_fd;
+	}
+	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
+	file->f_flags |= O_LARGEFILE;
+
+	restricted_file = restrictedmem_file_create(file);
+	if (IS_ERR(restricted_file)) {
+		err = PTR_ERR(restricted_file);
+		fput(file);
+		goto err_fd;
+	}
+
+	fd_install(fd, restricted_file);
+	return fd;
+err_fd:
+	put_unused_fd(fd);
+	return err;
+}
+
+void restrictedmem_register_notifier(struct file *file,
+				     struct restrictedmem_notifier *notifier)
+{
+	struct restrictedmem_data *data = file->f_mapping->private_data;
+
+	mutex_lock(&data->lock);
+	list_add(&notifier->list, &data->notifiers);
+	mutex_unlock(&data->lock);
+}
+EXPORT_SYMBOL_GPL(restrictedmem_register_notifier);
+
+void restrictedmem_unregister_notifier(struct file *file,
+				       struct restrictedmem_notifier *notifier)
+{
+	struct restrictedmem_data *data = file->f_mapping->private_data;
+
+	mutex_lock(&data->lock);
+	list_del(&notifier->list);
+	mutex_unlock(&data->lock);
+}
+EXPORT_SYMBOL_GPL(restrictedmem_unregister_notifier);
+
+int restrictedmem_get_page(struct file *file, pgoff_t offset,
+			   struct page **pagep, int *order)
+{
+	struct restrictedmem_data *data = file->f_mapping->private_data;
+	struct file *memfd = data->memfd;
+	struct folio *folio;
+	struct page *page;
+	int ret;
+
+	ret = shmem_get_folio(file_inode(memfd), offset, &folio, SGP_WRITE);
+	if (ret)
+		return ret;
+
+	page = folio_file_page(folio, offset);
+	*pagep = page;
+	if (order)
+		*order = thp_order(compound_head(page));
+
+	SetPageUptodate(page);
+	unlock_page(page);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(restrictedmem_get_page);
+
+void restrictedmem_error_page(struct page *page, struct address_space *mapping)
+{
+	struct super_block *sb = restrictedmem_mnt->mnt_sb;
+	struct inode *inode, *next;
+
+	if (!shmem_mapping(mapping))
+		return;
+
+	spin_lock(&sb->s_inode_list_lock);
+	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
+		struct restrictedmem_data *data = inode->i_mapping->private_data;
+		struct file *memfd = data->memfd;
+
+		if (memfd->f_mapping == mapping) {
+			pgoff_t start, end;
+
+			spin_unlock(&sb->s_inode_list_lock);
+
+			start = page->index;
+			end = start + thp_nr_pages(page);
+			restrictedmem_notifier_error(data, start, end);
+			return;
+		}
+	}
+	spin_unlock(&sb->s_inode_list_lock);
+}
-- 
2.25.1

[PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

In confidential computing usages, whether a page is private or shared is
necessary information for KVM to perform operations like page fault
handling, page zapping etc. There are other potential use cases for
per-page memory attributes, e.g. to make memory read-only (or no-exec,
or exec-only, etc.) without having to modify memslots.

Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
userspace to operate on the per-page memory attributes.
  - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
    a guest memory range.
  - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
    memory attributes.

KVM internally uses xarray to store the per-page memory attributes.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
---
 Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
 arch/x86/kvm/Kconfig           |  1 +
 include/linux/kvm_host.h       |  3 ++
 include/uapi/linux/kvm.h       | 17 ++++++++
 virt/kvm/Kconfig               |  3 ++
 virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
 6 files changed, 163 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 5617bc4f899f..bb2f709c0900 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
 The "pad" and "reserved" fields may be used for future extensions and should be
 set to 0s by userspace.
 
+4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
+-----------------------------------------
+
+:Capability: KVM_CAP_MEMORY_ATTRIBUTES
+:Architectures: x86
+:Type: vm ioctl
+:Parameters: u64 memory attributes bitmask(out)
+:Returns: 0 on success, <0 on error
+
+Returns supported memory attributes bitmask. Supported memory attributes will
+have the corresponding bits set in u64 memory attributes bitmask.
+
+The following memory attributes are defined::
+
+  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
+  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
+  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
+  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
+
+4.139 KVM_SET_MEMORY_ATTRIBUTES
+-----------------------------------------
+
+:Capability: KVM_CAP_MEMORY_ATTRIBUTES
+:Architectures: x86
+:Type: vm ioctl
+:Parameters: struct kvm_memory_attributes(in/out)
+:Returns: 0 on success, <0 on error
+
+Sets memory attributes for pages in a guest memory range. Parameters are
+specified via the following structure::
+
+  struct kvm_memory_attributes {
+	__u64 address;
+	__u64 size;
+	__u64 attributes;
+	__u64 flags;
+  };
+
+The user sets the per-page memory attributes to a guest memory range indicated
+by address/size, and in return KVM adjusts address and size to reflect the
+actual pages of the memory range have been successfully set to the attributes.
+If the call returns 0, "address" is updated to the last successful address + 1
+and "size" is updated to the remaining address size that has not been set
+successfully. The user should check the return value as well as the size to
+decide if the operation succeeded for the whole range or not. The user may want
+to retry the operation with the returned address/size if the previous range was
+partially successful.
+
+Both address and size should be page aligned and the supported attributes can be
+retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
+
+The "flags" field may be used for future extensions and should be set to 0s.
+
 5. The kvm_run structure
 ========================
 
@@ -8270,6 +8323,16 @@ structure.
 When getting the Modified Change Topology Report value, the attr->addr
 must point to a byte where the value will be stored or retrieved from.
 
+8.40 KVM_CAP_MEMORY_ATTRIBUTES
+------------------------------
+
+:Capability: KVM_CAP_MEMORY_ATTRIBUTES
+:Architectures: x86
+:Type: vm
+
+This capability indicates KVM supports per-page memory attributes and ioctls
+KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available.
+
 9. Known KVM API problems
 =========================
 
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index fbeaa9ddef59..a8e379a3afee 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -49,6 +49,7 @@ config KVM
 	select SRCU
 	select INTERVAL_TREE
 	select HAVE_KVM_PM_NOTIFIER if PM
+	select HAVE_KVM_MEMORY_ATTRIBUTES
 	help
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8f874a964313..a784e2b06625 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -800,6 +800,9 @@ struct kvm {
 
 #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
 	struct notifier_block pm_notifier;
+#endif
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+	struct xarray mem_attr_array;
 #endif
 	char stats_id[KVM_STATS_NAME_SIZE];
 };
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 64dfe9c07c87..5d0941acb5bb 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1182,6 +1182,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_S390_CPU_TOPOLOGY 222
 #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
 #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
+#define KVM_CAP_MEMORY_ATTRIBUTES 225
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -2238,4 +2239,20 @@ struct kvm_s390_zpci_op {
 /* flags for kvm_s390_zpci_op->u.reg_aen.flags */
 #define KVM_S390_ZPCIOP_REGAEN_HOST    (1 << 0)
 
+/* Available with KVM_CAP_MEMORY_ATTRIBUTES */
+#define KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES    _IOR(KVMIO,  0xd2, __u64)
+#define KVM_SET_MEMORY_ATTRIBUTES              _IOWR(KVMIO,  0xd3, struct kvm_memory_attributes)
+
+struct kvm_memory_attributes {
+	__u64 address;
+	__u64 size;
+	__u64 attributes;
+	__u64 flags;
+};
+
+#define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
+#define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
+#define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
+#define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
+
 #endif /* __LINUX_KVM_H */
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 800f9470e36b..effdea5dd4f0 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -19,6 +19,9 @@ config HAVE_KVM_IRQ_ROUTING
 config HAVE_KVM_DIRTY_RING
        bool
 
+config HAVE_KVM_MEMORY_ATTRIBUTES
+       bool
+
 # Only strongly ordered architectures can select this, as it doesn't
 # put any explicit constraint on userspace ordering. They can also
 # select the _ACQ_REL version.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1782c4555d94..7f0f5e9f2406 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 	spin_lock_init(&kvm->mn_invalidate_lock);
 	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
 	xa_init(&kvm->vcpu_array);
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+	xa_init(&kvm->mem_attr_array);
+#endif
 
 	INIT_LIST_HEAD(&kvm->gpc_list);
 	spin_lock_init(&kvm->gpc_lock);
@@ -1323,6 +1326,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
 		kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
 		kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
 	}
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+	xa_destroy(&kvm->mem_attr_array);
+#endif
 	cleanup_srcu_struct(&kvm->irq_srcu);
 	cleanup_srcu_struct(&kvm->srcu);
 	kvm_arch_free_vm(kvm);
@@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
 }
 #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
 
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+static u64 kvm_supported_mem_attributes(struct kvm *kvm)
+{
+	return 0;
+}
+
+static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
+					   struct kvm_memory_attributes *attrs)
+{
+	gfn_t start, end;
+	unsigned long i;
+	void *entry;
+	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
+
+	/* flags is currently not used. */
+	if (attrs->flags)
+		return -EINVAL;
+	if (attrs->attributes & ~supported_attrs)
+		return -EINVAL;
+	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
+		return -EINVAL;
+	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
+		return -EINVAL;
+
+	start = attrs->address >> PAGE_SHIFT;
+	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
+
+	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
+
+	mutex_lock(&kvm->lock);
+	for (i = start; i < end; i++)
+		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
+				    GFP_KERNEL_ACCOUNT)))
+			break;
+	mutex_unlock(&kvm->lock);
+
+	attrs->address = i << PAGE_SHIFT;
+	attrs->size = (end - i) << PAGE_SHIFT;
+
+	return 0;
+}
+#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
+
 struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
 {
 	return __gfn_to_memslot(kvm_memslots(kvm), gfn);
@@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 #ifdef CONFIG_HAVE_KVM_MSI
 	case KVM_CAP_SIGNAL_MSI:
 #endif
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+	case KVM_CAP_MEMORY_ATTRIBUTES:
+#endif
 #ifdef CONFIG_HAVE_KVM_IRQFD
 	case KVM_CAP_IRQFD:
 	case KVM_CAP_IRQFD_RESAMPLE:
@@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp,
 		break;
 	}
 #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+	case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: {
+		u64 attrs = kvm_supported_mem_attributes(kvm);
+
+		r = -EFAULT;
+		if (copy_to_user(argp, &attrs, sizeof(attrs)))
+			goto out;
+		r = 0;
+		break;
+	}
+	case KVM_SET_MEMORY_ATTRIBUTES: {
+		struct kvm_memory_attributes attrs;
+
+		r = -EFAULT;
+		if (copy_from_user(&attrs, argp, sizeof(attrs)))
+			goto out;
+
+		r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);
+
+		if (!r && copy_to_user(argp, &attrs, sizeof(attrs)))
+			r = -EFAULT;
+		break;
+	}
+#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
 	case KVM_CREATE_DEVICE: {
 		struct kvm_create_device cd;
 
-- 
2.25.1

[PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

In memory encryption usage, guest memory may be encrypted with special
key and can be accessed only by the guest itself. We call such memory
private memory. It's valueless and sometimes can cause problem to allow
userspace to access guest private memory. This new KVM memslot extension
allows guest private memory being provided through a restrictedmem
backed file descriptor(fd) and userspace is restricted to access the
bookmarked memory in the fd.

This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
additional KVM memslot fields restricted_fd/restricted_offset to allow
userspace to instruct KVM to provide guest memory through restricted_fd.
'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
and the size is 'memory_size'.

The extended memslot can still have the userspace_addr(hva). When use, a
single memslot can maintain both private memory through restricted_fd
and shared memory through userspace_addr. Whether the private or shared
part is visible to guest is maintained by other KVM code.

A restrictedmem_notifier field is also added to the memslot structure to
allow the restricted_fd's backing store to notify KVM the memory change,
KVM then can invalidate its page table entries or handle memory errors.

Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
and right now it is selected on X86_64 only.

To make future maintenance easy, internally use a binary compatible
alias struct kvm_user_mem_region to handle both the normal and the
'_ext' variants.

Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
---
 Documentation/virt/kvm/api.rst | 40 ++++++++++++++++++++++-----
 arch/x86/kvm/Kconfig           |  2 ++
 arch/x86/kvm/x86.c             |  2 +-
 include/linux/kvm_host.h       |  8 ++++--
 include/uapi/linux/kvm.h       | 28 +++++++++++++++++++
 virt/kvm/Kconfig               |  3 +++
 virt/kvm/kvm_main.c            | 49 ++++++++++++++++++++++++++++------
 7 files changed, 114 insertions(+), 18 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index bb2f709c0900..99352170c130 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1319,7 +1319,7 @@ yet and must be cleared on entry.
 :Capability: KVM_CAP_USER_MEMORY
 :Architectures: all
 :Type: vm ioctl
-:Parameters: struct kvm_userspace_memory_region (in)
+:Parameters: struct kvm_userspace_memory_region(_ext) (in)
 :Returns: 0 on success, -1 on error
 
 ::
@@ -1332,9 +1332,18 @@ yet and must be cleared on entry.
 	__u64 userspace_addr; /* start of the userspace allocated memory */
   };
 
+  struct kvm_userspace_memory_region_ext {
+	struct kvm_userspace_memory_region region;
+	__u64 restricted_offset;
+	__u32 restricted_fd;
+	__u32 pad1;
+	__u64 pad2[14];
+  };
+
   /* for kvm_memory_region::flags */
   #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
   #define KVM_MEM_READONLY	(1UL << 1)
+  #define KVM_MEM_PRIVATE		(1UL << 2)
 
 This ioctl allows the user to create, modify or delete a guest physical
 memory slot.  Bits 0-15 of "slot" specify the slot id and this value
@@ -1365,12 +1374,29 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
 be identical.  This allows large pages in the guest to be backed by large
 pages in the host.
 
-The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
-KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
-writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
-use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
-to make a new slot read-only.  In this case, writes to this memory will be
-posted to userspace as KVM_EXIT_MMIO exits.
+kvm_userspace_memory_region_ext struct includes all fields of
+kvm_userspace_memory_region struct, while also adds additional fields for some
+other features. See below description of flags field for more information.
+It's recommended to use kvm_userspace_memory_region_ext in new userspace code.
+
+The flags field supports following flags:
+
+- KVM_MEM_LOG_DIRTY_PAGES to instruct KVM to keep track of writes to memory
+  within the slot. For more details, see KVM_GET_DIRTY_LOG ioctl.
+
+- KVM_MEM_READONLY, if KVM_CAP_READONLY_MEM allows, to make a new slot
+  read-only. In this case, writes to this memory will be posted to userspace as
+  KVM_EXIT_MMIO exits.
+
+- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
+  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl), to indicate a new slot has private
+  memory backed by a file descriptor(fd) and userspace access to the fd may be
+  restricted. Userspace should use restricted_fd/restricted_offset in the
+  kvm_userspace_memory_region_ext to instruct KVM to provide private memory
+  to guest. Userspace should guarantee not to map the same host physical address
+  indicated by restricted_fd/restricted_offset to different guest physical
+  addresses within multiple memslots. Failed to do this may result undefined
+  behavior.
 
 When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
 the memory region are automatically reflected into the guest.  For example, an
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index a8e379a3afee..690cb21010e7 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -50,6 +50,8 @@ config KVM
 	select INTERVAL_TREE
 	select HAVE_KVM_PM_NOTIFIER if PM
 	select HAVE_KVM_MEMORY_ATTRIBUTES
+	select HAVE_KVM_RESTRICTED_MEM if X86_64
+	select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
 	help
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7f850dfb4086..9a07380f8d3c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12224,7 +12224,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
 	}
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
-		struct kvm_userspace_memory_region m;
+		struct kvm_user_mem_region m;
 
 		m.slot = id | (i << 16);
 		m.flags = 0;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a784e2b06625..02347e386ea2 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -44,6 +44,7 @@
 
 #include <asm/kvm_host.h>
 #include <linux/kvm_dirty_ring.h>
+#include <linux/restrictedmem.h>
 
 #ifndef KVM_MAX_VCPU_IDS
 #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
@@ -585,6 +586,9 @@ struct kvm_memory_slot {
 	u32 flags;
 	short id;
 	u16 as_id;
+	struct file *restricted_file;
+	loff_t restricted_offset;
+	struct restrictedmem_notifier notifier;
 };
 
 static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
@@ -1123,9 +1127,9 @@ enum kvm_mr_change {
 };
 
 int kvm_set_memory_region(struct kvm *kvm,
-			  const struct kvm_userspace_memory_region *mem);
+			  const struct kvm_user_mem_region *mem);
 int __kvm_set_memory_region(struct kvm *kvm,
-			    const struct kvm_userspace_memory_region *mem);
+			    const struct kvm_user_mem_region *mem);
 void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
 void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5d0941acb5bb..13bff963b8b0 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -103,6 +103,33 @@ struct kvm_userspace_memory_region {
 	__u64 userspace_addr; /* start of the userspace allocated memory */
 };
 
+struct kvm_userspace_memory_region_ext {
+	struct kvm_userspace_memory_region region;
+	__u64 restricted_offset;
+	__u32 restricted_fd;
+	__u32 pad1;
+	__u64 pad2[14];
+};
+
+#ifdef __KERNEL__
+/*
+ * kvm_user_mem_region is a kernel-only alias of kvm_userspace_memory_region_ext
+ * that "unpacks" kvm_userspace_memory_region so that KVM can directly access
+ * all fields from the top-level "extended" region.
+ */
+struct kvm_user_mem_region {
+	__u32 slot;
+	__u32 flags;
+	__u64 guest_phys_addr;
+	__u64 memory_size;
+	__u64 userspace_addr;
+	__u64 restricted_offset;
+	__u32 restricted_fd;
+	__u32 pad1;
+	__u64 pad2[14];
+};
+#endif
+
 /*
  * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
  * other bits are reserved for kvm internal use which are defined in
@@ -110,6 +137,7 @@ struct kvm_userspace_memory_region {
  */
 #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
 #define KVM_MEM_READONLY	(1UL << 1)
+#define KVM_MEM_PRIVATE		(1UL << 2)
 
 /* for KVM_IRQ_LINE */
 struct kvm_irq_level {
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index effdea5dd4f0..d605545d6dd1 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -89,3 +89,6 @@ config KVM_XFER_TO_GUEST_WORK
 
 config HAVE_KVM_PM_NOTIFIER
        bool
+
+config HAVE_KVM_RESTRICTED_MEM
+       bool
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7f0f5e9f2406..b882eb2c76a2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1532,7 +1532,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
 	}
 }
 
-static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
+static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
 {
 	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
 
@@ -1934,7 +1934,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
  * Must be called holding kvm->slots_lock for write.
  */
 int __kvm_set_memory_region(struct kvm *kvm,
-			    const struct kvm_userspace_memory_region *mem)
+			    const struct kvm_user_mem_region *mem)
 {
 	struct kvm_memory_slot *old, *new;
 	struct kvm_memslots *slots;
@@ -2038,7 +2038,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
 
 int kvm_set_memory_region(struct kvm *kvm,
-			  const struct kvm_userspace_memory_region *mem)
+			  const struct kvm_user_mem_region *mem)
 {
 	int r;
 
@@ -2050,7 +2050,7 @@ int kvm_set_memory_region(struct kvm *kvm,
 EXPORT_SYMBOL_GPL(kvm_set_memory_region);
 
 static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
-					  struct kvm_userspace_memory_region *mem)
+					  struct kvm_user_mem_region *mem)
 {
 	if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
 		return -EINVAL;
@@ -4698,6 +4698,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
 	return fd;
 }
 
+#define SANITY_CHECK_MEM_REGION_FIELD(field)					\
+do {										\
+	BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=		\
+		     offsetof(struct kvm_userspace_memory_region, field));	\
+	BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=		\
+		     sizeof_field(struct kvm_userspace_memory_region, field));	\
+} while (0)
+
+#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)					\
+do {											\
+	BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=			\
+		     offsetof(struct kvm_userspace_memory_region_ext, field));		\
+	BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=			\
+		     sizeof_field(struct kvm_userspace_memory_region_ext, field));	\
+} while (0)
+
+static void kvm_sanity_check_user_mem_region_alias(void)
+{
+	SANITY_CHECK_MEM_REGION_FIELD(slot);
+	SANITY_CHECK_MEM_REGION_FIELD(flags);
+	SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
+	SANITY_CHECK_MEM_REGION_FIELD(memory_size);
+	SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
+	SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_offset);
+	SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_fd);
+}
+
 static long kvm_vm_ioctl(struct file *filp,
 			   unsigned int ioctl, unsigned long arg)
 {
@@ -4721,14 +4748,20 @@ static long kvm_vm_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_SET_USER_MEMORY_REGION: {
-		struct kvm_userspace_memory_region kvm_userspace_mem;
+		struct kvm_user_mem_region mem;
+		unsigned long size = sizeof(struct kvm_userspace_memory_region);
+
+		kvm_sanity_check_user_mem_region_alias();
 
 		r = -EFAULT;
-		if (copy_from_user(&kvm_userspace_mem, argp,
-						sizeof(kvm_userspace_mem)))
+		if (copy_from_user(&mem, argp, size))
+			goto out;
+
+		r = -EINVAL;
+		if (mem.flags & KVM_MEM_PRIVATE)
 			goto out;
 
-		r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
+		r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
 		break;
 	}
 	case KVM_GET_DIRTY_LOG: {
-- 
2.25.1

[PATCH v10 4/9] KVM: Add KVM_EXIT_MEMORY_FAULT exit

[Chao Peng]

This new KVM exit allows userspace to handle memory-related errors. It
indicates an error happens in KVM at guest memory range [gpa, gpa+size).
The flags includes additional information for userspace to handle the
error. Currently bit 0 is defined as 'private memory' where '1'
indicates error happens due to private memory access and '0' indicates
error happens due to shared memory access.

When private memory is enabled, this new exit will be used for KVM to
exit to userspace for shared <-> private memory conversion in memory
encryption usage. In such usage, typically there are two kind of memory
conversions:
  - explicit conversion: happens when guest explicitly calls into KVM
    to map a range (as private or shared), KVM then exits to userspace
    to perform the map/unmap operations.
  - implicit conversion: happens in KVM page fault handler where KVM
    exits to userspace for an implicit conversion when the page is in a
    different state than requested (private or shared).

Suggested-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
---
 Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++++
 include/uapi/linux/kvm.h       |  8 ++++++++
 2 files changed, 30 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 99352170c130..d9edb14ce30b 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6634,6 +6634,28 @@ array field represents return values. The userspace should update the return
 values of SBI call before resuming the VCPU. For more details on RISC-V SBI
 spec refer, https://github.com/riscv/riscv-sbi-doc.
 
+::
+
+		/* KVM_EXIT_MEMORY_FAULT */
+		struct {
+  #define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1ULL << 0)
+			__u64 flags;
+			__u64 gpa;
+			__u64 size;
+		} memory;
+
+If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has
+encountered a memory error which is not handled by KVM kernel module and
+userspace may choose to handle it. The 'flags' field indicates the memory
+properties of the exit.
+
+ - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by
+   private memory access when the bit is set. Otherwise the memory error is
+   caused by shared memory access when the bit is clear.
+
+'gpa' and 'size' indicate the memory range the error occurs at. The userspace
+may handle the error and return to KVM to retry the previous memory access.
+
 ::
 
     /* KVM_EXIT_NOTIFY */
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 13bff963b8b0..c7e9d375a902 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -300,6 +300,7 @@ struct kvm_xen_exit {
 #define KVM_EXIT_RISCV_SBI        35
 #define KVM_EXIT_RISCV_CSR        36
 #define KVM_EXIT_NOTIFY           37
+#define KVM_EXIT_MEMORY_FAULT     38
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
@@ -541,6 +542,13 @@ struct kvm_run {
 #define KVM_NOTIFY_CONTEXT_INVALID	(1 << 0)
 			__u32 flags;
 		} notify;
+		/* KVM_EXIT_MEMORY_FAULT */
+		struct {
+#define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1ULL << 0)
+			__u64 flags;
+			__u64 gpa;
+			__u64 size;
+		} memory;
 		/* Fix the size of the union. */
 		char padding[256];
 	};
-- 
2.25.1

[PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry

[Chao Peng]

Currently in mmu_notifier invalidate path, hva range is recorded and
then checked against by mmu_notifier_retry_hva() in the page fault
handling path. However, for the to be introduced private memory, a page
fault may not have a hva associated, checking gfn(gpa) makes more sense.

For existing hva based shared memory, gfn is expected to also work. The
only downside is when aliasing multiple gfns to a single hva, the
current algorithm of checking multiple ranges could result in a much
larger range being rejected. Such aliasing should be uncommon, so the
impact is expected small.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 arch/x86/kvm/mmu/mmu.c   |  8 +++++---
 include/linux/kvm_host.h | 33 +++++++++++++++++++++------------
 virt/kvm/kvm_main.c      | 32 +++++++++++++++++++++++---------
 3 files changed, 49 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4736d7849c60..e2c70b5afa3e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4259,7 +4259,7 @@ static bool is_page_fault_stale(struct kvm_vcpu *vcpu,
 		return true;
 
 	return fault->slot &&
-	       mmu_invalidate_retry_hva(vcpu->kvm, mmu_seq, fault->hva);
+	       mmu_invalidate_retry_gfn(vcpu->kvm, mmu_seq, fault->gfn);
 }
 
 static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
@@ -6098,7 +6098,9 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 
 	write_lock(&kvm->mmu_lock);
 
-	kvm_mmu_invalidate_begin(kvm, gfn_start, gfn_end);
+	kvm_mmu_invalidate_begin(kvm);
+
+	kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
 
 	flush = kvm_rmap_zap_gfn_range(kvm, gfn_start, gfn_end);
 
@@ -6112,7 +6114,7 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 		kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
 						   gfn_end - gfn_start);
 
-	kvm_mmu_invalidate_end(kvm, gfn_start, gfn_end);
+	kvm_mmu_invalidate_end(kvm);
 
 	write_unlock(&kvm->mmu_lock);
 }
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 02347e386ea2..3d69484d2704 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -787,8 +787,8 @@ struct kvm {
 	struct mmu_notifier mmu_notifier;
 	unsigned long mmu_invalidate_seq;
 	long mmu_invalidate_in_progress;
-	unsigned long mmu_invalidate_range_start;
-	unsigned long mmu_invalidate_range_end;
+	gfn_t mmu_invalidate_range_start;
+	gfn_t mmu_invalidate_range_end;
 #endif
 	struct list_head devices;
 	u64 manual_dirty_log_protect;
@@ -1389,10 +1389,9 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
 void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
 #endif
 
-void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
-			      unsigned long end);
-void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
-			    unsigned long end);
+void kvm_mmu_invalidate_begin(struct kvm *kvm);
+void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end);
+void kvm_mmu_invalidate_end(struct kvm *kvm);
 
 long kvm_arch_dev_ioctl(struct file *filp,
 			unsigned int ioctl, unsigned long arg);
@@ -1963,9 +1962,9 @@ static inline int mmu_invalidate_retry(struct kvm *kvm, unsigned long mmu_seq)
 	return 0;
 }
 
-static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
+static inline int mmu_invalidate_retry_gfn(struct kvm *kvm,
 					   unsigned long mmu_seq,
-					   unsigned long hva)
+					   gfn_t gfn)
 {
 	lockdep_assert_held(&kvm->mmu_lock);
 	/*
@@ -1974,10 +1973,20 @@ static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
 	 * that might be being invalidated. Note that it may include some false
 	 * positives, due to shortcuts when handing concurrent invalidations.
 	 */
-	if (unlikely(kvm->mmu_invalidate_in_progress) &&
-	    hva >= kvm->mmu_invalidate_range_start &&
-	    hva < kvm->mmu_invalidate_range_end)
-		return 1;
+	if (unlikely(kvm->mmu_invalidate_in_progress)) {
+		/*
+		 * Dropping mmu_lock after bumping mmu_invalidate_in_progress
+		 * but before updating the range is a KVM bug.
+		 */
+		if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
+				 kvm->mmu_invalidate_range_end == INVALID_GPA))
+			return 1;
+
+		if (gfn >= kvm->mmu_invalidate_range_start &&
+		    gfn < kvm->mmu_invalidate_range_end)
+			return 1;
+	}
+
 	if (kvm->mmu_invalidate_seq != mmu_seq)
 		return 1;
 	return 0;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b882eb2c76a2..ad55dfbc75d7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -540,9 +540,7 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,
 
 typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
 
-typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
-			     unsigned long end);
-
+typedef void (*on_lock_fn_t)(struct kvm *kvm);
 typedef void (*on_unlock_fn_t)(struct kvm *kvm);
 
 struct kvm_hva_range {
@@ -628,7 +626,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 				locked = true;
 				KVM_MMU_LOCK(kvm);
 				if (!IS_KVM_NULL_FN(range->on_lock))
-					range->on_lock(kvm, range->start, range->end);
+					range->on_lock(kvm);
+
 				if (IS_KVM_NULL_FN(range->handler))
 					break;
 			}
@@ -715,8 +714,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
 	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
 }
 
-void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
-			      unsigned long end)
+void kvm_mmu_invalidate_begin(struct kvm *kvm)
 {
 	/*
 	 * The count increase must become visible at unlock time as no
@@ -724,6 +722,17 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
 	 * count is also read inside the mmu_lock critical section.
 	 */
 	kvm->mmu_invalidate_in_progress++;
+
+	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
+		kvm->mmu_invalidate_range_start = INVALID_GPA;
+		kvm->mmu_invalidate_range_end = INVALID_GPA;
+	}
+}
+
+void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
+{
+	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
+
 	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
 		kvm->mmu_invalidate_range_start = start;
 		kvm->mmu_invalidate_range_end = end;
@@ -744,6 +753,12 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
 	}
 }
 
+static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
+	return kvm_unmap_gfn_range(kvm, range);
+}
+
 static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 					const struct mmu_notifier_range *range)
 {
@@ -752,7 +767,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 		.start		= range->start,
 		.end		= range->end,
 		.pte		= __pte(0),
-		.handler	= kvm_unmap_gfn_range,
+		.handler	= kvm_mmu_unmap_gfn_range,
 		.on_lock	= kvm_mmu_invalidate_begin,
 		.on_unlock	= kvm_arch_guest_memory_reclaimed,
 		.flush_on_ret	= true,
@@ -791,8 +806,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	return 0;
 }
 
-void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
-			    unsigned long end)
+void kvm_mmu_invalidate_end(struct kvm *kvm)
 {
 	/*
 	 * This sequence increase will notify the kvm page fault that
-- 
2.25.1

[PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Chao Peng]

Unmap the existing guest mappings when memory attribute is changed
between shared and private. This is needed because shared pages and
private pages are from different backends, unmapping existing ones
gives a chance for page fault handler to re-populate the mappings
according to the new attribute.

Only architecture has private memory support needs this and the
supported architecture is expected to rewrite the weak
kvm_arch_has_private_mem().

Also, during memory attribute changing and the unmapping time frame,
page fault handler may happen in the same memory range and can cause
incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
page fault handler retry during this time frame.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 include/linux/kvm_host.h |   7 +-
 virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
 2 files changed, 116 insertions(+), 59 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 3d69484d2704..3331c0c92838 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
 #endif
 
-#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
 struct kvm_gfn_range {
 	struct kvm_memory_slot *slot;
 	gfn_t start;
@@ -264,6 +263,8 @@ struct kvm_gfn_range {
 	bool may_block;
 };
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
+
+#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
 bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
@@ -785,11 +786,12 @@ struct kvm {
 
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
 	struct mmu_notifier mmu_notifier;
+#endif
 	unsigned long mmu_invalidate_seq;
 	long mmu_invalidate_in_progress;
 	gfn_t mmu_invalidate_range_start;
 	gfn_t mmu_invalidate_range_end;
-#endif
+
 	struct list_head devices;
 	u64 manual_dirty_log_protect;
 	struct dentry *debugfs_dentry;
@@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
 int kvm_arch_post_init_vm(struct kvm *kvm);
 void kvm_arch_pre_destroy_vm(struct kvm *kvm);
 int kvm_arch_create_vm_debugfs(struct kvm *kvm);
+bool kvm_arch_has_private_mem(struct kvm *kvm);
 
 #ifndef __KVM_HAVE_ARCH_VM_ALLOC
 /*
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ad55dfbc75d7..4e1e1e113bf0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
 }
 EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
 
+void kvm_mmu_invalidate_begin(struct kvm *kvm)
+{
+	/*
+	 * The count increase must become visible at unlock time as no
+	 * spte can be established without taking the mmu_lock and
+	 * count is also read inside the mmu_lock critical section.
+	 */
+	kvm->mmu_invalidate_in_progress++;
+
+	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
+		kvm->mmu_invalidate_range_start = INVALID_GPA;
+		kvm->mmu_invalidate_range_end = INVALID_GPA;
+	}
+}
+
+void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
+{
+	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
+
+	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
+		kvm->mmu_invalidate_range_start = start;
+		kvm->mmu_invalidate_range_end = end;
+	} else {
+		/*
+		 * Fully tracking multiple concurrent ranges has diminishing
+		 * returns. Keep things simple and just find the minimal range
+		 * which includes the current and new ranges. As there won't be
+		 * enough information to subtract a range after its invalidate
+		 * completes, any ranges invalidated concurrently will
+		 * accumulate and persist until all outstanding invalidates
+		 * complete.
+		 */
+		kvm->mmu_invalidate_range_start =
+			min(kvm->mmu_invalidate_range_start, start);
+		kvm->mmu_invalidate_range_end =
+			max(kvm->mmu_invalidate_range_end, end);
+	}
+}
+
+void kvm_mmu_invalidate_end(struct kvm *kvm)
+{
+	/*
+	 * This sequence increase will notify the kvm page fault that
+	 * the page that is going to be mapped in the spte could have
+	 * been freed.
+	 */
+	kvm->mmu_invalidate_seq++;
+	smp_wmb();
+	/*
+	 * The above sequence increase must be visible before the
+	 * below count decrease, which is ensured by the smp_wmb above
+	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
+	 */
+	kvm->mmu_invalidate_in_progress--;
+}
+
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
 static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
 {
@@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
 	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
 }
 
-void kvm_mmu_invalidate_begin(struct kvm *kvm)
-{
-	/*
-	 * The count increase must become visible at unlock time as no
-	 * spte can be established without taking the mmu_lock and
-	 * count is also read inside the mmu_lock critical section.
-	 */
-	kvm->mmu_invalidate_in_progress++;
-
-	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
-		kvm->mmu_invalidate_range_start = INVALID_GPA;
-		kvm->mmu_invalidate_range_end = INVALID_GPA;
-	}
-}
-
-void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
-{
-	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
-
-	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
-		kvm->mmu_invalidate_range_start = start;
-		kvm->mmu_invalidate_range_end = end;
-	} else {
-		/*
-		 * Fully tracking multiple concurrent ranges has diminishing
-		 * returns. Keep things simple and just find the minimal range
-		 * which includes the current and new ranges. As there won't be
-		 * enough information to subtract a range after its invalidate
-		 * completes, any ranges invalidated concurrently will
-		 * accumulate and persist until all outstanding invalidates
-		 * complete.
-		 */
-		kvm->mmu_invalidate_range_start =
-			min(kvm->mmu_invalidate_range_start, start);
-		kvm->mmu_invalidate_range_end =
-			max(kvm->mmu_invalidate_range_end, end);
-	}
-}
-
 static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
@@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	return 0;
 }
 
-void kvm_mmu_invalidate_end(struct kvm *kvm)
-{
-	/*
-	 * This sequence increase will notify the kvm page fault that
-	 * the page that is going to be mapped in the spte could have
-	 * been freed.
-	 */
-	kvm->mmu_invalidate_seq++;
-	smp_wmb();
-	/*
-	 * The above sequence increase must be visible before the
-	 * below count decrease, which is ensured by the smp_wmb above
-	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
-	 */
-	kvm->mmu_invalidate_in_progress--;
-}
-
 static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
 					const struct mmu_notifier_range *range)
 {
@@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
 	return 0;
 }
 
+bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
+{
+	return false;
+}
+
 static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 {
 	struct kvm *kvm = kvm_arch_alloc_vm();
@@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
 	return 0;
 }
 
+static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
+{
+	struct kvm_gfn_range gfn_range;
+	struct kvm_memory_slot *slot;
+	struct kvm_memslots *slots;
+	struct kvm_memslot_iter iter;
+	int i;
+	int r = 0;
+
+	gfn_range.pte = __pte(0);
+	gfn_range.may_block = true;
+
+	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+		slots = __kvm_memslots(kvm, i);
+
+		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
+			slot = iter.slot;
+			gfn_range.start = max(start, slot->base_gfn);
+			gfn_range.end = min(end, slot->base_gfn + slot->npages);
+			if (gfn_range.start >= gfn_range.end)
+				continue;
+			gfn_range.slot = slot;
+
+			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
+		}
+	}
+
+	if (r)
+		kvm_flush_remote_tlbs(kvm);
+}
+
 static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
 					   struct kvm_memory_attributes *attrs)
 {
 	gfn_t start, end;
 	unsigned long i;
 	void *entry;
+	int idx;
 	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
 
-	/* flags is currently not used. */
+	/* 'flags' is currently not used. */
 	if (attrs->flags)
 		return -EINVAL;
 	if (attrs->attributes & ~supported_attrs)
@@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
 
 	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
 
+	if (kvm_arch_has_private_mem(kvm)) {
+		KVM_MMU_LOCK(kvm);
+		kvm_mmu_invalidate_begin(kvm);
+		kvm_mmu_invalidate_range_add(kvm, start, end);
+		KVM_MMU_UNLOCK(kvm);
+	}
+
 	mutex_lock(&kvm->lock);
 	for (i = start; i < end; i++)
 		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
@@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
 			break;
 	mutex_unlock(&kvm->lock);
 
+	if (kvm_arch_has_private_mem(kvm)) {
+		idx = srcu_read_lock(&kvm->srcu);
+		KVM_MMU_LOCK(kvm);
+		if (i > start)
+			kvm_unmap_mem_range(kvm, start, i);
+		kvm_mmu_invalidate_end(kvm);
+		KVM_MMU_UNLOCK(kvm);
+		srcu_read_unlock(&kvm->srcu, idx);
+	}
+
 	attrs->address = i << PAGE_SHIFT;
 	attrs->size = (end - i) << PAGE_SHIFT;
 
-- 
2.25.1

[PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Chao Peng]

A large page with mixed private/shared subpages can't be mapped as large
page since its sub private/shared pages are from different memory
backends and may also treated by architecture differently. When
private/shared memory are mixed in a large page, the current lpage_info
is not sufficient to decide whether the page can be mapped as large page
or not and additional private/shared mixed information is needed.

Tracking this 'mixed' information with the current 'count' like
disallow_lpage is a bit challenge so reserve a bit in 'disallow_lpage'
to indicate a large page has mixed private/share subpages and update
this 'mixed' bit whenever the memory attribute is changed between
private and shared.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 arch/x86/include/asm/kvm_host.h |   8 ++
 arch/x86/kvm/mmu/mmu.c          | 134 +++++++++++++++++++++++++++++++-
 arch/x86/kvm/x86.c              |   2 +
 include/linux/kvm_host.h        |  19 +++++
 virt/kvm/kvm_main.c             |   9 ++-
 5 files changed, 169 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 283cbb83d6ae..7772ab37ac89 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -38,6 +38,7 @@
 #include <asm/hyperv-tlfs.h>
 
 #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
+#define __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
 
 #define KVM_MAX_VCPUS 1024
 
@@ -1011,6 +1012,13 @@ struct kvm_vcpu_arch {
 #endif
 };
 
+/*
+ * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
+ * level. The remaining bits are used as a reference count.
+ */
+#define KVM_LPAGE_PRIVATE_SHARED_MIXED		(1U << 31)
+#define KVM_LPAGE_COUNT_MAX			((1U << 31) - 1)
+
 struct kvm_lpage_info {
 	int disallow_lpage;
 };
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e2c70b5afa3e..2190fd8c95c0 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -763,11 +763,16 @@ static void update_gfn_disallow_lpage_count(const struct kvm_memory_slot *slot,
 {
 	struct kvm_lpage_info *linfo;
 	int i;
+	int disallow_count;
 
 	for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
 		linfo = lpage_info_slot(gfn, slot, i);
+
+		disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
+		WARN_ON(disallow_count + count < 0 ||
+			disallow_count > KVM_LPAGE_COUNT_MAX - count);
+
 		linfo->disallow_lpage += count;
-		WARN_ON(linfo->disallow_lpage < 0);
 	}
 }
 
@@ -6986,3 +6991,130 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
 	if (kvm->arch.nx_huge_page_recovery_thread)
 		kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
 }
+
+static bool linfo_is_mixed(struct kvm_lpage_info *linfo)
+{
+	return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
+}
+
+static void linfo_set_mixed(gfn_t gfn, struct kvm_memory_slot *slot,
+			    int level, bool mixed)
+{
+	struct kvm_lpage_info *linfo = lpage_info_slot(gfn, slot, level);
+
+	if (mixed)
+		linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
+	else
+		linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
+}
+
+static bool is_expected_attr_entry(void *entry, unsigned long expected_attrs)
+{
+	bool expect_private = expected_attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
+
+	if (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) {
+		if (!expect_private)
+			return false;
+	} else if (expect_private)
+		return false;
+
+	return true;
+}
+
+static bool mem_attrs_mixed_2m(struct kvm *kvm, unsigned long attrs,
+			       gfn_t start, gfn_t end)
+{
+	XA_STATE(xas, &kvm->mem_attr_array, start);
+	gfn_t gfn = start;
+	void *entry;
+	bool mixed = false;
+
+	rcu_read_lock();
+	entry = xas_load(&xas);
+	while (gfn < end) {
+		if (xas_retry(&xas, entry))
+			continue;
+
+		KVM_BUG_ON(gfn != xas.xa_index, kvm);
+
+		if (!is_expected_attr_entry(entry, attrs)) {
+			mixed = true;
+			break;
+		}
+
+		entry = xas_next(&xas);
+		gfn++;
+	}
+
+	rcu_read_unlock();
+	return mixed;
+}
+
+static bool mem_attrs_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
+			    int level, unsigned long attrs,
+			    gfn_t start, gfn_t end)
+{
+	unsigned long gfn;
+
+	if (level == PG_LEVEL_2M)
+		return mem_attrs_mixed_2m(kvm, attrs, start, end);
+
+	for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1))
+		if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
+		    !is_expected_attr_entry(xa_load(&kvm->mem_attr_array, gfn),
+					    attrs))
+			return true;
+	return false;
+}
+
+static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
+						  struct kvm_memory_slot *slot,
+						  unsigned long attrs,
+						  gfn_t start, gfn_t end)
+{
+	unsigned long pages, mask;
+	gfn_t gfn, gfn_end, first, last;
+	int level;
+	bool mixed;
+
+	/*
+	 * The sequence matters here: we set the higher level basing on the
+	 * lower level's scanning result.
+	 */
+	for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
+		pages = KVM_PAGES_PER_HPAGE(level);
+		mask = ~(pages - 1);
+		first = start & mask;
+		last = (end - 1) & mask;
+
+		/*
+		 * We only need to scan the head and tail page, for middle pages
+		 * we know they will not be mixed.
+		 */
+		gfn = max(first, slot->base_gfn);
+		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
+		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
+		linfo_set_mixed(gfn, slot, level, mixed);
+
+		if (first == last)
+			return;
+
+		for (gfn = first + pages; gfn < last; gfn += pages)
+			linfo_set_mixed(gfn, slot, level, false);
+
+		gfn = last;
+		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
+		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
+		linfo_set_mixed(gfn, slot, level, mixed);
+	}
+}
+
+void kvm_arch_set_memory_attributes(struct kvm *kvm,
+				    struct kvm_memory_slot *slot,
+				    unsigned long attrs,
+				    gfn_t start, gfn_t end)
+{
+	if (kvm_slot_can_be_private(slot))
+		kvm_update_lpage_private_shared_mixed(kvm, slot, attrs,
+						      start, end);
+}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9a07380f8d3c..5aefcff614d2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
 		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
 			linfo[lpages - 1].disallow_lpage = 1;
 		ugfn = slot->userspace_addr >> PAGE_SHIFT;
+		if (kvm_slot_can_be_private(slot))
+			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
 		/*
 		 * If the gfn and userspace address are not aligned wrt each
 		 * other, disable large page support for this slot.
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 3331c0c92838..25099c94e770 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -592,6 +592,11 @@ struct kvm_memory_slot {
 	struct restrictedmem_notifier notifier;
 };
 
+static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
+{
+	return slot && (slot->flags & KVM_MEM_PRIVATE);
+}
+
 static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
 {
 	return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
@@ -2316,4 +2321,18 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
 /* Max number of entries allowed for each kvm dirty ring */
 #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
 
+#ifdef __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
+void kvm_arch_set_memory_attributes(struct kvm *kvm,
+				    struct kvm_memory_slot *slot,
+				    unsigned long attrs,
+				    gfn_t start, gfn_t end);
+#else
+static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
+						  struct kvm_memory_slot *slot,
+						  unsigned long attrs,
+						  gfn_t start, gfn_t end)
+{
+}
+#endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
+
 #endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4e1e1e113bf0..e107afea32f0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2354,7 +2354,8 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
 	return 0;
 }
 
-static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
+static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end,
+				unsigned long attrs)
 {
 	struct kvm_gfn_range gfn_range;
 	struct kvm_memory_slot *slot;
@@ -2378,6 +2379,10 @@ static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
 			gfn_range.slot = slot;
 
 			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
+
+			kvm_arch_set_memory_attributes(kvm, slot, attrs,
+						       gfn_range.start,
+						       gfn_range.end);
 		}
 	}
 
@@ -2427,7 +2432,7 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
 		idx = srcu_read_lock(&kvm->srcu);
 		KVM_MMU_LOCK(kvm);
 		if (i > start)
-			kvm_unmap_mem_range(kvm, start, i);
+			kvm_unmap_mem_range(kvm, start, i, attrs->attributes);
 		kvm_mmu_invalidate_end(kvm);
 		KVM_MMU_UNLOCK(kvm);
 		srcu_read_unlock(&kvm->srcu, idx);
-- 
2.25.1

[PATCH v10 8/9] KVM: Handle page fault for private memory

[Chao Peng]

A KVM_MEM_PRIVATE memslot can include both fd-based private memory and
hva-based shared memory. Architecture code (like TDX code) can tell
whether the on-going fault is private or not. This patch adds a
'is_private' field to kvm_page_fault to indicate this and architecture
code is expected to set it.

To handle page fault for such memslot, the handling logic is different
depending on whether the fault is private or shared. KVM checks if
'is_private' matches the host's view of the page (maintained in
mem_attr_array).
  - For a successful match, private pfn is obtained with
    restrictedmem_get_page() and shared pfn is obtained with existing
    get_user_pages().
  - For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
    userspace. Userspace then can convert memory between private/shared
    in host's view and retry the fault.

Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++++++++++++++--
 arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
 arch/x86/kvm/mmu/mmutrace.h     |  1 +
 arch/x86/kvm/mmu/tdp_mmu.c      |  2 +-
 include/linux/kvm_host.h        | 30 ++++++++++++++++
 5 files changed, 105 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 2190fd8c95c0..b1953ebc012e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3058,7 +3058,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
 
 int kvm_mmu_max_mapping_level(struct kvm *kvm,
 			      const struct kvm_memory_slot *slot, gfn_t gfn,
-			      int max_level)
+			      int max_level, bool is_private)
 {
 	struct kvm_lpage_info *linfo;
 	int host_level;
@@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
 			break;
 	}
 
+	if (is_private)
+		return max_level;
+
 	if (max_level == PG_LEVEL_4K)
 		return PG_LEVEL_4K;
 
@@ -3098,7 +3101,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	 * level, which will be used to do precise, accurate accounting.
 	 */
 	fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
-						     fault->gfn, fault->max_level);
+						     fault->gfn, fault->max_level,
+						     fault->is_private);
 	if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
 		return;
 
@@ -4178,6 +4182,49 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
 	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
 }
 
+static inline u8 order_to_level(int order)
+{
+	BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
+
+	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
+		return PG_LEVEL_1G;
+
+	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
+		return PG_LEVEL_2M;
+
+	return PG_LEVEL_4K;
+}
+
+static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
+				    struct kvm_page_fault *fault)
+{
+	vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
+	if (fault->is_private)
+		vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
+	else
+		vcpu->run->memory.flags = 0;
+	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
+	vcpu->run->memory.size = PAGE_SIZE;
+	return RET_PF_USER;
+}
+
+static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
+				   struct kvm_page_fault *fault)
+{
+	int order;
+	struct kvm_memory_slot *slot = fault->slot;
+
+	if (!kvm_slot_can_be_private(slot))
+		return kvm_do_memory_fault_exit(vcpu, fault);
+
+	if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
+		return RET_PF_RETRY;
+
+	fault->max_level = min(order_to_level(order), fault->max_level);
+	fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
+	return RET_PF_CONTINUE;
+}
+
 static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 {
 	struct kvm_memory_slot *slot = fault->slot;
@@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 			return RET_PF_EMULATE;
 	}
 
+	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
+		return kvm_do_memory_fault_exit(vcpu, fault);
+
+	if (fault->is_private)
+		return kvm_faultin_pfn_private(vcpu, fault);
+
 	async = false;
 	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
 					  fault->write, &fault->map_writable,
@@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 			return -EIO;
 	}
 
+	if (r == RET_PF_USER)
+		return 0;
+
 	if (r < 0)
 		return r;
 	if (r != RET_PF_EMULATE)
@@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
 		 */
 		if (sp->role.direct &&
 		    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
-							       PG_LEVEL_NUM)) {
+							       PG_LEVEL_NUM,
+							       false)) {
 			kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
 
 			if (kvm_available_flush_tlb_with_range())
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index dbaf6755c5a7..5ccf08183b00 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -189,6 +189,7 @@ struct kvm_page_fault {
 
 	/* Derived from mmu and global state.  */
 	const bool is_tdp;
+	const bool is_private;
 	const bool nx_huge_page_workaround_enabled;
 
 	/*
@@ -237,6 +238,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
  * RET_PF_RETRY: let CPU fault again on the address.
  * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
  * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
+ * RET_PF_USER: need to exit to userspace to handle this fault.
  * RET_PF_FIXED: The faulting entry has been fixed.
  * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
  *
@@ -253,6 +255,7 @@ enum {
 	RET_PF_RETRY,
 	RET_PF_EMULATE,
 	RET_PF_INVALID,
+	RET_PF_USER,
 	RET_PF_FIXED,
 	RET_PF_SPURIOUS,
 };
@@ -310,7 +313,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 
 int kvm_mmu_max_mapping_level(struct kvm *kvm,
 			      const struct kvm_memory_slot *slot, gfn_t gfn,
-			      int max_level);
+			      int max_level, bool is_private);
 void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
 void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
 
@@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
 void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
 void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
 
+#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
+static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
+					gfn_t gfn, kvm_pfn_t *pfn, int *order)
+{
+	WARN_ON_ONCE(1);
+	return -EOPNOTSUPP;
+}
+#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
+
 #endif /* __KVM_X86_MMU_INTERNAL_H */
diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
index ae86820cef69..2d7555381955 100644
--- a/arch/x86/kvm/mmu/mmutrace.h
+++ b/arch/x86/kvm/mmu/mmutrace.h
@@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
 TRACE_DEFINE_ENUM(RET_PF_RETRY);
 TRACE_DEFINE_ENUM(RET_PF_EMULATE);
 TRACE_DEFINE_ENUM(RET_PF_INVALID);
+TRACE_DEFINE_ENUM(RET_PF_USER);
 TRACE_DEFINE_ENUM(RET_PF_FIXED);
 TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
 
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 771210ce5181..8ba1a4afc546 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1768,7 +1768,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
 			continue;
 
 		max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
-							      iter.gfn, PG_LEVEL_NUM);
+						iter.gfn, PG_LEVEL_NUM, false);
 		if (max_mapping_level < iter.level)
 			continue;
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 25099c94e770..153842bb33df 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
 }
 #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
 
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
+{
+	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
+	       KVM_MEMORY_ATTRIBUTE_PRIVATE;
+}
+#else
+static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
+{
+	return false;
+}
+
+#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
+
+#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
+static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
+					gfn_t gfn, kvm_pfn_t *pfn, int *order)
+{
+	int ret;
+	struct page *page;
+	pgoff_t index = gfn - slot->base_gfn +
+			(slot->restricted_offset >> PAGE_SHIFT);
+
+	ret = restrictedmem_get_page(slot->restricted_file, index,
+				     &page, order);
+	*pfn = page_to_pfn(page);
+	return ret;
+}
+#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
+
 #endif
-- 
2.25.1

[PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

Register/unregister private memslot to fd-based memory backing store
restrictedmem and implement the callbacks for restrictedmem_notifier:
  - invalidate_start()/invalidate_end() to zap the existing memory
    mappings in the KVM page table.
  - error() to request KVM_REQ_MEMORY_MCE and later exit to userspace
    with KVM_EXIT_SHUTDOWN.

Expose KVM_MEM_PRIVATE for memslot and KVM_MEMORY_ATTRIBUTE_PRIVATE for
KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to userspace but either are
controlled by kvm_arch_has_private_mem() which should be rewritten by
architecture code.

Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
---
 arch/x86/include/asm/kvm_host.h |   1 +
 arch/x86/kvm/x86.c              |  13 +++
 include/linux/kvm_host.h        |   3 +
 virt/kvm/kvm_main.c             | 179 +++++++++++++++++++++++++++++++-
 4 files changed, 191 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7772ab37ac89..27ef31133352 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -114,6 +114,7 @@
 	KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_HV_TLB_FLUSH \
 	KVM_ARCH_REQ_FLAGS(32, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_MEMORY_MCE		KVM_ARCH_REQ(33)
 
 #define CR0_RESERVED_BITS                                               \
 	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5aefcff614d2..c67e22f3e2ee 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6587,6 +6587,13 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned long state)
 }
 #endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */
 
+#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
+void kvm_arch_memory_mce(struct kvm *kvm)
+{
+	kvm_make_all_cpus_request(kvm, KVM_REQ_MEMORY_MCE);
+}
+#endif
+
 static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_clock_data data = { 0 };
@@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
 			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
+
+		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
+			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
+			r = 0;
+			goto out;
+		}
 	}
 
 	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 153842bb33df..f032d878e034 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -590,6 +590,7 @@ struct kvm_memory_slot {
 	struct file *restricted_file;
 	loff_t restricted_offset;
 	struct restrictedmem_notifier notifier;
+	struct kvm *kvm;
 };
 
 static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
@@ -2363,6 +2364,8 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
 	*pfn = page_to_pfn(page);
 	return ret;
 }
+
+void kvm_arch_memory_mce(struct kvm *kvm);
 #endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
 
 #endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e107afea32f0..ac835fc77273 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -936,6 +936,121 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
 
 #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
 
+#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
+static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
+					 pgoff_t start, pgoff_t end,
+					 gfn_t *gfn_start, gfn_t *gfn_end)
+{
+	unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
+
+	if (start > base_pgoff)
+		*gfn_start = slot->base_gfn + start - base_pgoff;
+	else
+		*gfn_start = slot->base_gfn;
+
+	if (end < base_pgoff + slot->npages)
+		*gfn_end = slot->base_gfn + end - base_pgoff;
+	else
+		*gfn_end = slot->base_gfn + slot->npages;
+
+	if (*gfn_start >= *gfn_end)
+		return false;
+
+	return true;
+}
+
+static void kvm_restrictedmem_invalidate_begin(struct restrictedmem_notifier *notifier,
+					       pgoff_t start, pgoff_t end)
+{
+	struct kvm_memory_slot *slot = container_of(notifier,
+						    struct kvm_memory_slot,
+						    notifier);
+	struct kvm *kvm = slot->kvm;
+	gfn_t gfn_start, gfn_end;
+	struct kvm_gfn_range gfn_range;
+	int idx;
+
+	if (!restrictedmem_range_is_valid(slot, start, end,
+					  &gfn_start, &gfn_end))
+		return;
+
+	gfn_range.start = gfn_start;
+	gfn_range.end = gfn_end;
+	gfn_range.slot = slot;
+	gfn_range.pte = __pte(0);
+	gfn_range.may_block = true;
+
+	idx = srcu_read_lock(&kvm->srcu);
+	KVM_MMU_LOCK(kvm);
+
+	kvm_mmu_invalidate_begin(kvm);
+	kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
+	if (kvm_unmap_gfn_range(kvm, &gfn_range))
+		kvm_flush_remote_tlbs(kvm);
+
+	KVM_MMU_UNLOCK(kvm);
+	srcu_read_unlock(&kvm->srcu, idx);
+}
+
+static void kvm_restrictedmem_invalidate_end(struct restrictedmem_notifier *notifier,
+					     pgoff_t start, pgoff_t end)
+{
+	struct kvm_memory_slot *slot = container_of(notifier,
+						    struct kvm_memory_slot,
+						    notifier);
+	struct kvm *kvm = slot->kvm;
+	gfn_t gfn_start, gfn_end;
+
+	if (!restrictedmem_range_is_valid(slot, start, end,
+					  &gfn_start, &gfn_end))
+		return;
+
+	KVM_MMU_LOCK(kvm);
+	kvm_mmu_invalidate_end(kvm);
+	KVM_MMU_UNLOCK(kvm);
+}
+
+static void kvm_restrictedmem_error(struct restrictedmem_notifier *notifier,
+				    pgoff_t start, pgoff_t end)
+{
+	struct kvm_memory_slot *slot = container_of(notifier,
+						    struct kvm_memory_slot,
+						    notifier);
+	kvm_arch_memory_mce(slot->kvm);
+}
+
+static struct restrictedmem_notifier_ops kvm_restrictedmem_notifier_ops = {
+	.invalidate_start = kvm_restrictedmem_invalidate_begin,
+	.invalidate_end = kvm_restrictedmem_invalidate_end,
+	.error = kvm_restrictedmem_error,
+};
+
+static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
+{
+	slot->notifier.ops = &kvm_restrictedmem_notifier_ops;
+	restrictedmem_register_notifier(slot->restricted_file, &slot->notifier);
+}
+
+static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
+{
+	restrictedmem_unregister_notifier(slot->restricted_file,
+					  &slot->notifier);
+}
+
+#else /* !CONFIG_HAVE_KVM_RESTRICTED_MEM */
+
+static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
+{
+	WARN_ON_ONCE(1);
+}
+
+static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
+{
+	WARN_ON_ONCE(1);
+}
+
+#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
+
 #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
 static int kvm_pm_notifier_call(struct notifier_block *bl,
 				unsigned long state,
@@ -980,6 +1095,11 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
 /* This does not remove the slot from struct kvm_memslots data structures */
 static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 {
+	if (slot->flags & KVM_MEM_PRIVATE) {
+		kvm_restrictedmem_unregister(slot);
+		fput(slot->restricted_file);
+	}
+
 	kvm_destroy_dirty_bitmap(slot);
 
 	kvm_arch_free_memslot(kvm, slot);
@@ -1551,10 +1671,14 @@ static void kvm_replace_memslot(struct kvm *kvm,
 	}
 }
 
-static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
+static int check_memory_region_flags(struct kvm *kvm,
+				     const struct kvm_user_mem_region *mem)
 {
 	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
 
+	if (kvm_arch_has_private_mem(kvm))
+		valid_flags |= KVM_MEM_PRIVATE;
+
 #ifdef __KVM_HAVE_READONLY_MEM
 	valid_flags |= KVM_MEM_READONLY;
 #endif
@@ -1630,6 +1754,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
 {
 	int r;
 
+	if (change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
+		kvm_restrictedmem_register(new);
+
 	/*
 	 * If dirty logging is disabled, nullify the bitmap; the old bitmap
 	 * will be freed on "commit".  If logging is enabled in both old and
@@ -1658,6 +1785,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
 	if (r && new && new->dirty_bitmap && (!old || !old->dirty_bitmap))
 		kvm_destroy_dirty_bitmap(new);
 
+	if (r && change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
+		kvm_restrictedmem_unregister(new);
+
 	return r;
 }
 
@@ -1963,7 +2093,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	int as_id, id;
 	int r;
 
-	r = check_memory_region_flags(mem);
+	r = check_memory_region_flags(kvm, mem);
 	if (r)
 		return r;
 
@@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
 			mem->memory_size))
 		return -EINVAL;
+	if (mem->flags & KVM_MEM_PRIVATE &&
+		(mem->restricted_offset & (PAGE_SIZE - 1) ||
+		 mem->restricted_offset > U64_MAX - mem->memory_size))
+		return -EINVAL;
 	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
 		return -EINVAL;
 	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
@@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
 			return -EINVAL;
 	} else { /* Modify an existing slot. */
+		/* Private memslots are immutable, they can only be deleted. */
+		if (mem->flags & KVM_MEM_PRIVATE)
+			return -EINVAL;
 		if ((mem->userspace_addr != old->userspace_addr) ||
 		    (npages != old->npages) ||
 		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
@@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	new->npages = npages;
 	new->flags = mem->flags;
 	new->userspace_addr = mem->userspace_addr;
+	if (mem->flags & KVM_MEM_PRIVATE) {
+		new->restricted_file = fget(mem->restricted_fd);
+		if (!new->restricted_file ||
+		    !file_is_restrictedmem(new->restricted_file)) {
+			r = -EINVAL;
+			goto out;
+		}
+		new->restricted_offset = mem->restricted_offset;
+	}
+
+	new->kvm = kvm;
 
 	r = kvm_set_memslot(kvm, old, new, change);
 	if (r)
-		kfree(new);
+		goto out;
+
+	return 0;
+
+out:
+	if (new->restricted_file)
+		fput(new->restricted_file);
+	kfree(new);
 	return r;
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
@@ -2351,6 +2506,8 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
 #ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
 static u64 kvm_supported_mem_attributes(struct kvm *kvm)
 {
+	if (kvm_arch_has_private_mem(kvm))
+		return KVM_MEMORY_ATTRIBUTE_PRIVATE;
 	return 0;
 }
 
@@ -4822,16 +4979,28 @@ static long kvm_vm_ioctl(struct file *filp,
 	}
 	case KVM_SET_USER_MEMORY_REGION: {
 		struct kvm_user_mem_region mem;
-		unsigned long size = sizeof(struct kvm_userspace_memory_region);
+		unsigned int flags_offset = offsetof(typeof(mem), flags);
+		unsigned long size;
+		u32 flags;
 
 		kvm_sanity_check_user_mem_region_alias();
 
+		memset(&mem, 0, sizeof(mem));
+
 		r = -EFAULT;
+		if (get_user(flags, (u32 __user *)(argp + flags_offset)))
+			goto out;
+
+		if (flags & KVM_MEM_PRIVATE)
+			size = sizeof(struct kvm_userspace_memory_region_ext);
+		else
+			size = sizeof(struct kvm_userspace_memory_region);
+
 		if (copy_from_user(&mem, argp, size))
 			goto out;
 
 		r = -EINVAL;
-		if (mem.flags & KVM_MEM_PRIVATE)
+		if ((flags ^ mem.flags) & KVM_MEM_PRIVATE)
 			goto out;
 
 		r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
-- 
2.25.1

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Fuad Tabba]

Hi Chao,

On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> In memory encryption usage, guest memory may be encrypted with special
> key and can be accessed only by the guest itself. We call such memory
> private memory. It's valueless and sometimes can cause problem to allow
> userspace to access guest private memory. This new KVM memslot extension
> allows guest private memory being provided through a restrictedmem
> backed file descriptor(fd) and userspace is restricted to access the
> bookmarked memory in the fd.
>
> This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> additional KVM memslot fields restricted_fd/restricted_offset to allow
> userspace to instruct KVM to provide guest memory through restricted_fd.
> 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> and the size is 'memory_size'.
>
> The extended memslot can still have the userspace_addr(hva). When use, a
> single memslot can maintain both private memory through restricted_fd
> and shared memory through userspace_addr. Whether the private or shared
> part is visible to guest is maintained by other KVM code.
>
> A restrictedmem_notifier field is also added to the memslot structure to
> allow the restricted_fd's backing store to notify KVM the memory change,
> KVM then can invalidate its page table entries or handle memory errors.
>
> Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> and right now it is selected on X86_64 only.
>
> To make future maintenance easy, internally use a binary compatible
> alias struct kvm_user_mem_region to handle both the normal and the
> '_ext' variants.
>
> Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>

V9 of this patch [*] had KVM_CAP_PRIVATE_MEM, but it's not in this
patch series anymore. Any reason you removed it, or is it just an
omission?

[*] https://lore.kernel.org/linux-mm/20221025151344.3784230-3-chao.p.peng@linux.intel.com/

Thanks,
/fuad

> ---
>  Documentation/virt/kvm/api.rst | 40 ++++++++++++++++++++++-----
>  arch/x86/kvm/Kconfig           |  2 ++
>  arch/x86/kvm/x86.c             |  2 +-
>  include/linux/kvm_host.h       |  8 ++++--
>  include/uapi/linux/kvm.h       | 28 +++++++++++++++++++
>  virt/kvm/Kconfig               |  3 +++
>  virt/kvm/kvm_main.c            | 49 ++++++++++++++++++++++++++++------
>  7 files changed, 114 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index bb2f709c0900..99352170c130 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -1319,7 +1319,7 @@ yet and must be cleared on entry.
>  :Capability: KVM_CAP_USER_MEMORY
>  :Architectures: all
>  :Type: vm ioctl
> -:Parameters: struct kvm_userspace_memory_region (in)
> +:Parameters: struct kvm_userspace_memory_region(_ext) (in)
>  :Returns: 0 on success, -1 on error
>
>  ::
> @@ -1332,9 +1332,18 @@ yet and must be cleared on entry.
>         __u64 userspace_addr; /* start of the userspace allocated memory */
>    };
>
> +  struct kvm_userspace_memory_region_ext {
> +       struct kvm_userspace_memory_region region;
> +       __u64 restricted_offset;
> +       __u32 restricted_fd;
> +       __u32 pad1;
> +       __u64 pad2[14];
> +  };
> +
>    /* for kvm_memory_region::flags */
>    #define KVM_MEM_LOG_DIRTY_PAGES      (1UL << 0)
>    #define KVM_MEM_READONLY     (1UL << 1)
> +  #define KVM_MEM_PRIVATE              (1UL << 2)
>
>  This ioctl allows the user to create, modify or delete a guest physical
>  memory slot.  Bits 0-15 of "slot" specify the slot id and this value
> @@ -1365,12 +1374,29 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
>  be identical.  This allows large pages in the guest to be backed by large
>  pages in the host.
>
> -The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
> -KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
> -writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
> -use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
> -to make a new slot read-only.  In this case, writes to this memory will be
> -posted to userspace as KVM_EXIT_MMIO exits.
> +kvm_userspace_memory_region_ext struct includes all fields of
> +kvm_userspace_memory_region struct, while also adds additional fields for some
> +other features. See below description of flags field for more information.
> +It's recommended to use kvm_userspace_memory_region_ext in new userspace code.
> +
> +The flags field supports following flags:
> +
> +- KVM_MEM_LOG_DIRTY_PAGES to instruct KVM to keep track of writes to memory
> +  within the slot. For more details, see KVM_GET_DIRTY_LOG ioctl.
> +
> +- KVM_MEM_READONLY, if KVM_CAP_READONLY_MEM allows, to make a new slot
> +  read-only. In this case, writes to this memory will be posted to userspace as
> +  KVM_EXIT_MMIO exits.
> +
> +- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
> +  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl), to indicate a new slot has private
> +  memory backed by a file descriptor(fd) and userspace access to the fd may be
> +  restricted. Userspace should use restricted_fd/restricted_offset in the
> +  kvm_userspace_memory_region_ext to instruct KVM to provide private memory
> +  to guest. Userspace should guarantee not to map the same host physical address
> +  indicated by restricted_fd/restricted_offset to different guest physical
> +  addresses within multiple memslots. Failed to do this may result undefined
> +  behavior.
>
>  When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
>  the memory region are automatically reflected into the guest.  For example, an
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index a8e379a3afee..690cb21010e7 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -50,6 +50,8 @@ config KVM
>         select INTERVAL_TREE
>         select HAVE_KVM_PM_NOTIFIER if PM
>         select HAVE_KVM_MEMORY_ATTRIBUTES
> +       select HAVE_KVM_RESTRICTED_MEM if X86_64
> +       select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
>         help
>           Support hosting fully virtualized guest machines using hardware
>           virtualization extensions.  You will need a fairly recent
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7f850dfb4086..9a07380f8d3c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12224,7 +12224,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
>         }
>
>         for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> -               struct kvm_userspace_memory_region m;
> +               struct kvm_user_mem_region m;
>
>                 m.slot = id | (i << 16);
>                 m.flags = 0;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a784e2b06625..02347e386ea2 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -44,6 +44,7 @@
>
>  #include <asm/kvm_host.h>
>  #include <linux/kvm_dirty_ring.h>
> +#include <linux/restrictedmem.h>
>
>  #ifndef KVM_MAX_VCPU_IDS
>  #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
> @@ -585,6 +586,9 @@ struct kvm_memory_slot {
>         u32 flags;
>         short id;
>         u16 as_id;
> +       struct file *restricted_file;
> +       loff_t restricted_offset;
> +       struct restrictedmem_notifier notifier;
>  };
>
>  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
> @@ -1123,9 +1127,9 @@ enum kvm_mr_change {
>  };
>
>  int kvm_set_memory_region(struct kvm *kvm,
> -                         const struct kvm_userspace_memory_region *mem);
> +                         const struct kvm_user_mem_region *mem);
>  int __kvm_set_memory_region(struct kvm *kvm,
> -                           const struct kvm_userspace_memory_region *mem);
> +                           const struct kvm_user_mem_region *mem);
>  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
>  void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
>  int kvm_arch_prepare_memory_region(struct kvm *kvm,
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 5d0941acb5bb..13bff963b8b0 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -103,6 +103,33 @@ struct kvm_userspace_memory_region {
>         __u64 userspace_addr; /* start of the userspace allocated memory */
>  };
>
> +struct kvm_userspace_memory_region_ext {
> +       struct kvm_userspace_memory_region region;
> +       __u64 restricted_offset;
> +       __u32 restricted_fd;
> +       __u32 pad1;
> +       __u64 pad2[14];
> +};
> +
> +#ifdef __KERNEL__
> +/*
> + * kvm_user_mem_region is a kernel-only alias of kvm_userspace_memory_region_ext
> + * that "unpacks" kvm_userspace_memory_region so that KVM can directly access
> + * all fields from the top-level "extended" region.
> + */
> +struct kvm_user_mem_region {
> +       __u32 slot;
> +       __u32 flags;
> +       __u64 guest_phys_addr;
> +       __u64 memory_size;
> +       __u64 userspace_addr;
> +       __u64 restricted_offset;
> +       __u32 restricted_fd;
> +       __u32 pad1;
> +       __u64 pad2[14];
> +};
> +#endif
> +
>  /*
>   * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
>   * other bits are reserved for kvm internal use which are defined in
> @@ -110,6 +137,7 @@ struct kvm_userspace_memory_region {
>   */
>  #define KVM_MEM_LOG_DIRTY_PAGES        (1UL << 0)
>  #define KVM_MEM_READONLY       (1UL << 1)
> +#define KVM_MEM_PRIVATE                (1UL << 2)
>
>  /* for KVM_IRQ_LINE */
>  struct kvm_irq_level {
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index effdea5dd4f0..d605545d6dd1 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -89,3 +89,6 @@ config KVM_XFER_TO_GUEST_WORK
>
>  config HAVE_KVM_PM_NOTIFIER
>         bool
> +
> +config HAVE_KVM_RESTRICTED_MEM
> +       bool
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7f0f5e9f2406..b882eb2c76a2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1532,7 +1532,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
>         }
>  }
>
> -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
> +static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
>  {
>         u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
>
> @@ -1934,7 +1934,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
>   * Must be called holding kvm->slots_lock for write.
>   */
>  int __kvm_set_memory_region(struct kvm *kvm,
> -                           const struct kvm_userspace_memory_region *mem)
> +                           const struct kvm_user_mem_region *mem)
>  {
>         struct kvm_memory_slot *old, *new;
>         struct kvm_memslots *slots;
> @@ -2038,7 +2038,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
>
>  int kvm_set_memory_region(struct kvm *kvm,
> -                         const struct kvm_userspace_memory_region *mem)
> +                         const struct kvm_user_mem_region *mem)
>  {
>         int r;
>
> @@ -2050,7 +2050,7 @@ int kvm_set_memory_region(struct kvm *kvm,
>  EXPORT_SYMBOL_GPL(kvm_set_memory_region);
>
>  static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
> -                                         struct kvm_userspace_memory_region *mem)
> +                                         struct kvm_user_mem_region *mem)
>  {
>         if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
>                 return -EINVAL;
> @@ -4698,6 +4698,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
>         return fd;
>  }
>
> +#define SANITY_CHECK_MEM_REGION_FIELD(field)                                   \
> +do {                                                                           \
> +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=             \
> +                    offsetof(struct kvm_userspace_memory_region, field));      \
> +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=         \
> +                    sizeof_field(struct kvm_userspace_memory_region, field));  \
> +} while (0)
> +
> +#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)                                       \
> +do {                                                                                   \
> +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=                     \
> +                    offsetof(struct kvm_userspace_memory_region_ext, field));          \
> +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=                 \
> +                    sizeof_field(struct kvm_userspace_memory_region_ext, field));      \
> +} while (0)
> +
> +static void kvm_sanity_check_user_mem_region_alias(void)
> +{
> +       SANITY_CHECK_MEM_REGION_FIELD(slot);
> +       SANITY_CHECK_MEM_REGION_FIELD(flags);
> +       SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
> +       SANITY_CHECK_MEM_REGION_FIELD(memory_size);
> +       SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
> +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_offset);
> +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_fd);
> +}
> +
>  static long kvm_vm_ioctl(struct file *filp,
>                            unsigned int ioctl, unsigned long arg)
>  {
> @@ -4721,14 +4748,20 @@ static long kvm_vm_ioctl(struct file *filp,
>                 break;
>         }
>         case KVM_SET_USER_MEMORY_REGION: {
> -               struct kvm_userspace_memory_region kvm_userspace_mem;
> +               struct kvm_user_mem_region mem;
> +               unsigned long size = sizeof(struct kvm_userspace_memory_region);
> +
> +               kvm_sanity_check_user_mem_region_alias();
>
>                 r = -EFAULT;
> -               if (copy_from_user(&kvm_userspace_mem, argp,
> -                                               sizeof(kvm_userspace_mem)))
> +               if (copy_from_user(&mem, argp, size))
> +                       goto out;
> +
> +               r = -EINVAL;
> +               if (mem.flags & KVM_MEM_PRIVATE)
>                         goto out;
>
> -               r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
> +               r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
>                 break;
>         }
>         case KVM_GET_DIRTY_LOG: {
> --
> 2.25.1
>

Re: [PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry

[Fuad Tabba]

Hi Chao,

On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> Currently in mmu_notifier invalidate path, hva range is recorded and
> then checked against by mmu_notifier_retry_hva() in the page fault
> handling path. However, for the to be introduced private memory, a page
> fault may not have a hva associated, checking gfn(gpa) makes more sense.
>
> For existing hva based shared memory, gfn is expected to also work. The
> only downside is when aliasing multiple gfns to a single hva, the
> current algorithm of checking multiple ranges could result in a much
> larger range being rejected. Such aliasing should be uncommon, so the
> impact is expected small.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  arch/x86/kvm/mmu/mmu.c   |  8 +++++---
>  include/linux/kvm_host.h | 33 +++++++++++++++++++++------------
>  virt/kvm/kvm_main.c      | 32 +++++++++++++++++++++++---------
>  3 files changed, 49 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4736d7849c60..e2c70b5afa3e 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4259,7 +4259,7 @@ static bool is_page_fault_stale(struct kvm_vcpu *vcpu,
>                 return true;
>
>         return fault->slot &&
> -              mmu_invalidate_retry_hva(vcpu->kvm, mmu_seq, fault->hva);
> +              mmu_invalidate_retry_gfn(vcpu->kvm, mmu_seq, fault->gfn);
>  }
>
>  static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> @@ -6098,7 +6098,9 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>
>         write_lock(&kvm->mmu_lock);
>
> -       kvm_mmu_invalidate_begin(kvm, gfn_start, gfn_end);
> +       kvm_mmu_invalidate_begin(kvm);
> +
> +       kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
>
>         flush = kvm_rmap_zap_gfn_range(kvm, gfn_start, gfn_end);
>
> @@ -6112,7 +6114,7 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>                 kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
>                                                    gfn_end - gfn_start);
>
> -       kvm_mmu_invalidate_end(kvm, gfn_start, gfn_end);
> +       kvm_mmu_invalidate_end(kvm);
>
>         write_unlock(&kvm->mmu_lock);
>  }
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 02347e386ea2..3d69484d2704 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -787,8 +787,8 @@ struct kvm {
>         struct mmu_notifier mmu_notifier;
>         unsigned long mmu_invalidate_seq;
>         long mmu_invalidate_in_progress;
> -       unsigned long mmu_invalidate_range_start;
> -       unsigned long mmu_invalidate_range_end;
> +       gfn_t mmu_invalidate_range_start;
> +       gfn_t mmu_invalidate_range_end;
>  #endif
>         struct list_head devices;
>         u64 manual_dirty_log_protect;
> @@ -1389,10 +1389,9 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
>  void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
>  #endif
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> -                             unsigned long end);
> -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> -                           unsigned long end);
> +void kvm_mmu_invalidate_begin(struct kvm *kvm);
> +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end);
> +void kvm_mmu_invalidate_end(struct kvm *kvm);
>
>  long kvm_arch_dev_ioctl(struct file *filp,
>                         unsigned int ioctl, unsigned long arg);
> @@ -1963,9 +1962,9 @@ static inline int mmu_invalidate_retry(struct kvm *kvm, unsigned long mmu_seq)
>         return 0;
>  }
>
> -static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
> +static inline int mmu_invalidate_retry_gfn(struct kvm *kvm,
>                                            unsigned long mmu_seq,
> -                                          unsigned long hva)
> +                                          gfn_t gfn)
>  {
>         lockdep_assert_held(&kvm->mmu_lock);
>         /*
> @@ -1974,10 +1973,20 @@ static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
>          * that might be being invalidated. Note that it may include some false

nit: "might be" (or) "is being"

>          * positives, due to shortcuts when handing concurrent invalidations.

nit: handling

>          */
> -       if (unlikely(kvm->mmu_invalidate_in_progress) &&
> -           hva >= kvm->mmu_invalidate_range_start &&
> -           hva < kvm->mmu_invalidate_range_end)
> -               return 1;
> +       if (unlikely(kvm->mmu_invalidate_in_progress)) {
> +               /*
> +                * Dropping mmu_lock after bumping mmu_invalidate_in_progress
> +                * but before updating the range is a KVM bug.
> +                */
> +               if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
> +                                kvm->mmu_invalidate_range_end == INVALID_GPA))

INVALID_GPA is an x86-specific define in
arch/x86/include/asm/kvm_host.h, so this doesn't build on other
architectures. The obvious fix is to move it to
include/linux/kvm_host.h.

Cheers,
/fuad

> +                       return 1;
> +
> +               if (gfn >= kvm->mmu_invalidate_range_start &&
> +                   gfn < kvm->mmu_invalidate_range_end)
> +                       return 1;
> +       }
> +
>         if (kvm->mmu_invalidate_seq != mmu_seq)
>                 return 1;
>         return 0;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index b882eb2c76a2..ad55dfbc75d7 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -540,9 +540,7 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,
>
>  typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
>
> -typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
> -                            unsigned long end);
> -
> +typedef void (*on_lock_fn_t)(struct kvm *kvm);
>  typedef void (*on_unlock_fn_t)(struct kvm *kvm);
>
>  struct kvm_hva_range {
> @@ -628,7 +626,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
>                                 locked = true;
>                                 KVM_MMU_LOCK(kvm);
>                                 if (!IS_KVM_NULL_FN(range->on_lock))
> -                                       range->on_lock(kvm, range->start, range->end);
> +                                       range->on_lock(kvm);
> +
>                                 if (IS_KVM_NULL_FN(range->handler))
>                                         break;
>                         }
> @@ -715,8 +714,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
>         kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
>  }
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> -                             unsigned long end)
> +void kvm_mmu_invalidate_begin(struct kvm *kvm)
>  {
>         /*
>          * The count increase must become visible at unlock time as no
> @@ -724,6 +722,17 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
>          * count is also read inside the mmu_lock critical section.
>          */
>         kvm->mmu_invalidate_in_progress++;
> +
> +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +               kvm->mmu_invalidate_range_start = INVALID_GPA;
> +               kvm->mmu_invalidate_range_end = INVALID_GPA;
> +       }
> +}
> +
> +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> +
>         if (likely(kvm->mmu_invalidate_in_progress == 1)) {
>                 kvm->mmu_invalidate_range_start = start;
>                 kvm->mmu_invalidate_range_end = end;
> @@ -744,6 +753,12 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
>         }
>  }
>
> +static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> +{
> +       kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> +       return kvm_unmap_gfn_range(kvm, range);
> +}
> +
>  static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>                                         const struct mmu_notifier_range *range)
>  {
> @@ -752,7 +767,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>                 .start          = range->start,
>                 .end            = range->end,
>                 .pte            = __pte(0),
> -               .handler        = kvm_unmap_gfn_range,
> +               .handler        = kvm_mmu_unmap_gfn_range,
>                 .on_lock        = kvm_mmu_invalidate_begin,
>                 .on_unlock      = kvm_arch_guest_memory_reclaimed,
>                 .flush_on_ret   = true,
> @@ -791,8 +806,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>         return 0;
>  }
>
> -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> -                           unsigned long end)
> +void kvm_mmu_invalidate_end(struct kvm *kvm)
>  {
>         /*
>          * This sequence increase will notify the kvm page fault that
> --
> 2.25.1
>

Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Isaku Yamahata]

On Fri, Dec 02, 2022 at 02:13:45PM +0800,
Chao Peng <chao.p.peng@linux.intel.com> wrote:

> A large page with mixed private/shared subpages can't be mapped as large
> page since its sub private/shared pages are from different memory
> backends and may also treated by architecture differently. When
> private/shared memory are mixed in a large page, the current lpage_info
> is not sufficient to decide whether the page can be mapped as large page
> or not and additional private/shared mixed information is needed.
> 
> Tracking this 'mixed' information with the current 'count' like
> disallow_lpage is a bit challenge so reserve a bit in 'disallow_lpage'
> to indicate a large page has mixed private/share subpages and update
> this 'mixed' bit whenever the memory attribute is changed between
> private and shared.
> 
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  arch/x86/include/asm/kvm_host.h |   8 ++
>  arch/x86/kvm/mmu/mmu.c          | 134 +++++++++++++++++++++++++++++++-
>  arch/x86/kvm/x86.c              |   2 +
>  include/linux/kvm_host.h        |  19 +++++
>  virt/kvm/kvm_main.c             |   9 ++-
>  5 files changed, 169 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 283cbb83d6ae..7772ab37ac89 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -38,6 +38,7 @@
>  #include <asm/hyperv-tlfs.h>
>  
>  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
> +#define __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
>  
>  #define KVM_MAX_VCPUS 1024
>  
> @@ -1011,6 +1012,13 @@ struct kvm_vcpu_arch {
>  #endif
>  };
>  
> +/*
> + * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
> + * level. The remaining bits are used as a reference count.
> + */
> +#define KVM_LPAGE_PRIVATE_SHARED_MIXED		(1U << 31)
> +#define KVM_LPAGE_COUNT_MAX			((1U << 31) - 1)
> +
>  struct kvm_lpage_info {
>  	int disallow_lpage;
>  };
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e2c70b5afa3e..2190fd8c95c0 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -763,11 +763,16 @@ static void update_gfn_disallow_lpage_count(const struct kvm_memory_slot *slot,
>  {
>  	struct kvm_lpage_info *linfo;
>  	int i;
> +	int disallow_count;
>  
>  	for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
>  		linfo = lpage_info_slot(gfn, slot, i);
> +
> +		disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
> +		WARN_ON(disallow_count + count < 0 ||
> +			disallow_count > KVM_LPAGE_COUNT_MAX - count);
> +
>  		linfo->disallow_lpage += count;
> -		WARN_ON(linfo->disallow_lpage < 0);
>  	}
>  }
>  
> @@ -6986,3 +6991,130 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
>  	if (kvm->arch.nx_huge_page_recovery_thread)
>  		kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
>  }
> +
> +static bool linfo_is_mixed(struct kvm_lpage_info *linfo)
> +{
> +	return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +}
> +
> +static void linfo_set_mixed(gfn_t gfn, struct kvm_memory_slot *slot,
> +			    int level, bool mixed)
> +{
> +	struct kvm_lpage_info *linfo = lpage_info_slot(gfn, slot, level);
> +
> +	if (mixed)
> +		linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +	else
> +		linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +}
> +
> +static bool is_expected_attr_entry(void *entry, unsigned long expected_attrs)
> +{
> +	bool expect_private = expected_attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +
> +	if (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) {
> +		if (!expect_private)
> +			return false;
> +	} else if (expect_private)
> +		return false;
> +
> +	return true;
> +}
> +
> +static bool mem_attrs_mixed_2m(struct kvm *kvm, unsigned long attrs,
> +			       gfn_t start, gfn_t end)
> +{
> +	XA_STATE(xas, &kvm->mem_attr_array, start);
> +	gfn_t gfn = start;
> +	void *entry;
> +	bool mixed = false;
> +
> +	rcu_read_lock();
> +	entry = xas_load(&xas);
> +	while (gfn < end) {
> +		if (xas_retry(&xas, entry))
> +			continue;
> +
> +		KVM_BUG_ON(gfn != xas.xa_index, kvm);
> +
> +		if (!is_expected_attr_entry(entry, attrs)) {
> +			mixed = true;
> +			break;
> +		}
> +
> +		entry = xas_next(&xas);
> +		gfn++;
> +	}
> +
> +	rcu_read_unlock();
> +	return mixed;
> +}
> +
> +static bool mem_attrs_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
> +			    int level, unsigned long attrs,
> +			    gfn_t start, gfn_t end)
> +{
> +	unsigned long gfn;
> +
> +	if (level == PG_LEVEL_2M)
> +		return mem_attrs_mixed_2m(kvm, attrs, start, end);
> +
> +	for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1))
> +		if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
> +		    !is_expected_attr_entry(xa_load(&kvm->mem_attr_array, gfn),
> +					    attrs))
> +			return true;
> +	return false;
> +}
> +
> +static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
> +						  struct kvm_memory_slot *slot,
> +						  unsigned long attrs,
> +						  gfn_t start, gfn_t end)
> +{
> +	unsigned long pages, mask;
> +	gfn_t gfn, gfn_end, first, last;
> +	int level;
> +	bool mixed;
> +
> +	/*
> +	 * The sequence matters here: we set the higher level basing on the
> +	 * lower level's scanning result.
> +	 */
> +	for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> +		pages = KVM_PAGES_PER_HPAGE(level);
> +		mask = ~(pages - 1);
> +		first = start & mask;
> +		last = (end - 1) & mask;
> +
> +		/*
> +		 * We only need to scan the head and tail page, for middle pages
> +		 * we know they will not be mixed.
> +		 */
> +		gfn = max(first, slot->base_gfn);
> +		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
> +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> +		linfo_set_mixed(gfn, slot, level, mixed);
> +
> +		if (first == last)
> +			return;


continue.

> +
> +		for (gfn = first + pages; gfn < last; gfn += pages)
> +			linfo_set_mixed(gfn, slot, level, false);
> +
> +		gfn = last;
> +		gfn_end = min(last + pages, slot->base_gfn + slot->npages);

if (gfn == gfn_end) continue.


> +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> +		linfo_set_mixed(gfn, slot, level, mixed);
> +	}
> +}
> +
> +void kvm_arch_set_memory_attributes(struct kvm *kvm,
> +				    struct kvm_memory_slot *slot,
> +				    unsigned long attrs,
> +				    gfn_t start, gfn_t end)
> +{
> +	if (kvm_slot_can_be_private(slot))
> +		kvm_update_lpage_private_shared_mixed(kvm, slot, attrs,
> +						      start, end);
> +}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a07380f8d3c..5aefcff614d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
>  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
>  			linfo[lpages - 1].disallow_lpage = 1;
>  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> +		if (kvm_slot_can_be_private(slot))
> +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;

Is there any alignment restriction? If no, It should be +=.
In practice, alignment will hold though.

Thanks,

>  		/*
>  		 * If the gfn and userspace address are not aligned wrt each
>  		 * other, disable large page support for this slot.
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3331c0c92838..25099c94e770 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -592,6 +592,11 @@ struct kvm_memory_slot {
>  	struct restrictedmem_notifier notifier;
>  };
>  
> +static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
> +{
> +	return slot && (slot->flags & KVM_MEM_PRIVATE);
> +}
> +
>  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
>  {
>  	return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
> @@ -2316,4 +2321,18 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
>  /* Max number of entries allowed for each kvm dirty ring */
>  #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
>  
> +#ifdef __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
> +void kvm_arch_set_memory_attributes(struct kvm *kvm,
> +				    struct kvm_memory_slot *slot,
> +				    unsigned long attrs,
> +				    gfn_t start, gfn_t end);
> +#else
> +static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> +						  struct kvm_memory_slot *slot,
> +						  unsigned long attrs,
> +						  gfn_t start, gfn_t end)
> +{
> +}
> +#endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
> +
>  #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4e1e1e113bf0..e107afea32f0 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2354,7 +2354,8 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>  	return 0;
>  }
>  
> -static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end,
> +				unsigned long attrs)
>  {
>  	struct kvm_gfn_range gfn_range;
>  	struct kvm_memory_slot *slot;
> @@ -2378,6 +2379,10 @@ static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
>  			gfn_range.slot = slot;
>  
>  			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> +
> +			kvm_arch_set_memory_attributes(kvm, slot, attrs,
> +						       gfn_range.start,
> +						       gfn_range.end);
>  		}
>  	}
>  
> @@ -2427,7 +2432,7 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  		idx = srcu_read_lock(&kvm->srcu);
>  		KVM_MMU_LOCK(kvm);
>  		if (i > start)
> -			kvm_unmap_mem_range(kvm, start, i);
> +			kvm_unmap_mem_range(kvm, start, i, attrs->attributes);
>  		kvm_mmu_invalidate_end(kvm);
>  		KVM_MMU_UNLOCK(kvm);
>  		srcu_read_unlock(&kvm->srcu, idx);
> -- 
> 2.25.1
> 

-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Mon, Dec 05, 2022 at 09:03:11AM +0000, Fuad Tabba wrote:
> Hi Chao,
> 
> On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > In memory encryption usage, guest memory may be encrypted with special
> > key and can be accessed only by the guest itself. We call such memory
> > private memory. It's valueless and sometimes can cause problem to allow
> > userspace to access guest private memory. This new KVM memslot extension
> > allows guest private memory being provided through a restrictedmem
> > backed file descriptor(fd) and userspace is restricted to access the
> > bookmarked memory in the fd.
> >
> > This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> > additional KVM memslot fields restricted_fd/restricted_offset to allow
> > userspace to instruct KVM to provide guest memory through restricted_fd.
> > 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> > and the size is 'memory_size'.
> >
> > The extended memslot can still have the userspace_addr(hva). When use, a
> > single memslot can maintain both private memory through restricted_fd
> > and shared memory through userspace_addr. Whether the private or shared
> > part is visible to guest is maintained by other KVM code.
> >
> > A restrictedmem_notifier field is also added to the memslot structure to
> > allow the restricted_fd's backing store to notify KVM the memory change,
> > KVM then can invalidate its page table entries or handle memory errors.
> >
> > Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> > and right now it is selected on X86_64 only.
> >
> > To make future maintenance easy, internally use a binary compatible
> > alias struct kvm_user_mem_region to handle both the normal and the
> > '_ext' variants.
> >
> > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > Reviewed-by: Fuad Tabba <tabba@google.com>
> > Tested-by: Fuad Tabba <tabba@google.com>
> 
> V9 of this patch [*] had KVM_CAP_PRIVATE_MEM, but it's not in this
> patch series anymore. Any reason you removed it, or is it just an
> omission?

We had some discussion in v9 [1] to add generic memory attributes ioctls
and KVM_CAP_PRIVATE_MEM can be implemented as a new 
KVM_MEMORY_ATTRIBUTE_PRIVATE flag via KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES()
ioctl [2]. The api doc has been updated:

+- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
+  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl) …


[1] https://lore.kernel.org/linux-mm/Y2WB48kD0J4VGynX@google.com/
[2]
https://lore.kernel.org/linux-mm/20221202061347.1070246-3-chao.p.peng@linux.intel.com/

Thanks,
Chao
> 
> [*] https://lore.kernel.org/linux-mm/20221025151344.3784230-3-chao.p.peng@linux.intel.com/
> 
> Thanks,
> /fuad
> 
> > ---
> >  Documentation/virt/kvm/api.rst | 40 ++++++++++++++++++++++-----
> >  arch/x86/kvm/Kconfig           |  2 ++
> >  arch/x86/kvm/x86.c             |  2 +-
> >  include/linux/kvm_host.h       |  8 ++++--
> >  include/uapi/linux/kvm.h       | 28 +++++++++++++++++++
> >  virt/kvm/Kconfig               |  3 +++
> >  virt/kvm/kvm_main.c            | 49 ++++++++++++++++++++++++++++------
> >  7 files changed, 114 insertions(+), 18 deletions(-)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index bb2f709c0900..99352170c130 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -1319,7 +1319,7 @@ yet and must be cleared on entry.
> >  :Capability: KVM_CAP_USER_MEMORY
> >  :Architectures: all
> >  :Type: vm ioctl
> > -:Parameters: struct kvm_userspace_memory_region (in)
> > +:Parameters: struct kvm_userspace_memory_region(_ext) (in)
> >  :Returns: 0 on success, -1 on error
> >
> >  ::
> > @@ -1332,9 +1332,18 @@ yet and must be cleared on entry.
> >         __u64 userspace_addr; /* start of the userspace allocated memory */
> >    };
> >
> > +  struct kvm_userspace_memory_region_ext {
> > +       struct kvm_userspace_memory_region region;
> > +       __u64 restricted_offset;
> > +       __u32 restricted_fd;
> > +       __u32 pad1;
> > +       __u64 pad2[14];
> > +  };
> > +
> >    /* for kvm_memory_region::flags */
> >    #define KVM_MEM_LOG_DIRTY_PAGES      (1UL << 0)
> >    #define KVM_MEM_READONLY     (1UL << 1)
> > +  #define KVM_MEM_PRIVATE              (1UL << 2)
> >
> >  This ioctl allows the user to create, modify or delete a guest physical
> >  memory slot.  Bits 0-15 of "slot" specify the slot id and this value
> > @@ -1365,12 +1374,29 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
> >  be identical.  This allows large pages in the guest to be backed by large
> >  pages in the host.
> >
> > -The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
> > -KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
> > -writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
> > -use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
> > -to make a new slot read-only.  In this case, writes to this memory will be
> > -posted to userspace as KVM_EXIT_MMIO exits.
> > +kvm_userspace_memory_region_ext struct includes all fields of
> > +kvm_userspace_memory_region struct, while also adds additional fields for some
> > +other features. See below description of flags field for more information.
> > +It's recommended to use kvm_userspace_memory_region_ext in new userspace code.
> > +
> > +The flags field supports following flags:
> > +
> > +- KVM_MEM_LOG_DIRTY_PAGES to instruct KVM to keep track of writes to memory
> > +  within the slot. For more details, see KVM_GET_DIRTY_LOG ioctl.
> > +
> > +- KVM_MEM_READONLY, if KVM_CAP_READONLY_MEM allows, to make a new slot
> > +  read-only. In this case, writes to this memory will be posted to userspace as
> > +  KVM_EXIT_MMIO exits.
> > +
> > +- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
> > +  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl), to indicate a new slot has private
> > +  memory backed by a file descriptor(fd) and userspace access to the fd may be
> > +  restricted. Userspace should use restricted_fd/restricted_offset in the
> > +  kvm_userspace_memory_region_ext to instruct KVM to provide private memory
> > +  to guest. Userspace should guarantee not to map the same host physical address
> > +  indicated by restricted_fd/restricted_offset to different guest physical
> > +  addresses within multiple memslots. Failed to do this may result undefined
> > +  behavior.
> >
> >  When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
> >  the memory region are automatically reflected into the guest.  For example, an
> > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > index a8e379a3afee..690cb21010e7 100644
> > --- a/arch/x86/kvm/Kconfig
> > +++ b/arch/x86/kvm/Kconfig
> > @@ -50,6 +50,8 @@ config KVM
> >         select INTERVAL_TREE
> >         select HAVE_KVM_PM_NOTIFIER if PM
> >         select HAVE_KVM_MEMORY_ATTRIBUTES
> > +       select HAVE_KVM_RESTRICTED_MEM if X86_64
> > +       select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
> >         help
> >           Support hosting fully virtualized guest machines using hardware
> >           virtualization extensions.  You will need a fairly recent
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 7f850dfb4086..9a07380f8d3c 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -12224,7 +12224,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
> >         }
> >
> >         for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > -               struct kvm_userspace_memory_region m;
> > +               struct kvm_user_mem_region m;
> >
> >                 m.slot = id | (i << 16);
> >                 m.flags = 0;
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index a784e2b06625..02347e386ea2 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -44,6 +44,7 @@
> >
> >  #include <asm/kvm_host.h>
> >  #include <linux/kvm_dirty_ring.h>
> > +#include <linux/restrictedmem.h>
> >
> >  #ifndef KVM_MAX_VCPU_IDS
> >  #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
> > @@ -585,6 +586,9 @@ struct kvm_memory_slot {
> >         u32 flags;
> >         short id;
> >         u16 as_id;
> > +       struct file *restricted_file;
> > +       loff_t restricted_offset;
> > +       struct restrictedmem_notifier notifier;
> >  };
> >
> >  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
> > @@ -1123,9 +1127,9 @@ enum kvm_mr_change {
> >  };
> >
> >  int kvm_set_memory_region(struct kvm *kvm,
> > -                         const struct kvm_userspace_memory_region *mem);
> > +                         const struct kvm_user_mem_region *mem);
> >  int __kvm_set_memory_region(struct kvm *kvm,
> > -                           const struct kvm_userspace_memory_region *mem);
> > +                           const struct kvm_user_mem_region *mem);
> >  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
> >  void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
> >  int kvm_arch_prepare_memory_region(struct kvm *kvm,
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index 5d0941acb5bb..13bff963b8b0 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -103,6 +103,33 @@ struct kvm_userspace_memory_region {
> >         __u64 userspace_addr; /* start of the userspace allocated memory */
> >  };
> >
> > +struct kvm_userspace_memory_region_ext {
> > +       struct kvm_userspace_memory_region region;
> > +       __u64 restricted_offset;
> > +       __u32 restricted_fd;
> > +       __u32 pad1;
> > +       __u64 pad2[14];
> > +};
> > +
> > +#ifdef __KERNEL__
> > +/*
> > + * kvm_user_mem_region is a kernel-only alias of kvm_userspace_memory_region_ext
> > + * that "unpacks" kvm_userspace_memory_region so that KVM can directly access
> > + * all fields from the top-level "extended" region.
> > + */
> > +struct kvm_user_mem_region {
> > +       __u32 slot;
> > +       __u32 flags;
> > +       __u64 guest_phys_addr;
> > +       __u64 memory_size;
> > +       __u64 userspace_addr;
> > +       __u64 restricted_offset;
> > +       __u32 restricted_fd;
> > +       __u32 pad1;
> > +       __u64 pad2[14];
> > +};
> > +#endif
> > +
> >  /*
> >   * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
> >   * other bits are reserved for kvm internal use which are defined in
> > @@ -110,6 +137,7 @@ struct kvm_userspace_memory_region {
> >   */
> >  #define KVM_MEM_LOG_DIRTY_PAGES        (1UL << 0)
> >  #define KVM_MEM_READONLY       (1UL << 1)
> > +#define KVM_MEM_PRIVATE                (1UL << 2)
> >
> >  /* for KVM_IRQ_LINE */
> >  struct kvm_irq_level {
> > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> > index effdea5dd4f0..d605545d6dd1 100644
> > --- a/virt/kvm/Kconfig
> > +++ b/virt/kvm/Kconfig
> > @@ -89,3 +89,6 @@ config KVM_XFER_TO_GUEST_WORK
> >
> >  config HAVE_KVM_PM_NOTIFIER
> >         bool
> > +
> > +config HAVE_KVM_RESTRICTED_MEM
> > +       bool
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 7f0f5e9f2406..b882eb2c76a2 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1532,7 +1532,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
> >         }
> >  }
> >
> > -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
> > +static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> >  {
> >         u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> >
> > @@ -1934,7 +1934,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
> >   * Must be called holding kvm->slots_lock for write.
> >   */
> >  int __kvm_set_memory_region(struct kvm *kvm,
> > -                           const struct kvm_userspace_memory_region *mem)
> > +                           const struct kvm_user_mem_region *mem)
> >  {
> >         struct kvm_memory_slot *old, *new;
> >         struct kvm_memslots *slots;
> > @@ -2038,7 +2038,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >  EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> >
> >  int kvm_set_memory_region(struct kvm *kvm,
> > -                         const struct kvm_userspace_memory_region *mem)
> > +                         const struct kvm_user_mem_region *mem)
> >  {
> >         int r;
> >
> > @@ -2050,7 +2050,7 @@ int kvm_set_memory_region(struct kvm *kvm,
> >  EXPORT_SYMBOL_GPL(kvm_set_memory_region);
> >
> >  static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
> > -                                         struct kvm_userspace_memory_region *mem)
> > +                                         struct kvm_user_mem_region *mem)
> >  {
> >         if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
> >                 return -EINVAL;
> > @@ -4698,6 +4698,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
> >         return fd;
> >  }
> >
> > +#define SANITY_CHECK_MEM_REGION_FIELD(field)                                   \
> > +do {                                                                           \
> > +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=             \
> > +                    offsetof(struct kvm_userspace_memory_region, field));      \
> > +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=         \
> > +                    sizeof_field(struct kvm_userspace_memory_region, field));  \
> > +} while (0)
> > +
> > +#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)                                       \
> > +do {                                                                                   \
> > +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=                     \
> > +                    offsetof(struct kvm_userspace_memory_region_ext, field));          \
> > +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=                 \
> > +                    sizeof_field(struct kvm_userspace_memory_region_ext, field));      \
> > +} while (0)
> > +
> > +static void kvm_sanity_check_user_mem_region_alias(void)
> > +{
> > +       SANITY_CHECK_MEM_REGION_FIELD(slot);
> > +       SANITY_CHECK_MEM_REGION_FIELD(flags);
> > +       SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
> > +       SANITY_CHECK_MEM_REGION_FIELD(memory_size);
> > +       SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
> > +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_offset);
> > +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_fd);
> > +}
> > +
> >  static long kvm_vm_ioctl(struct file *filp,
> >                            unsigned int ioctl, unsigned long arg)
> >  {
> > @@ -4721,14 +4748,20 @@ static long kvm_vm_ioctl(struct file *filp,
> >                 break;
> >         }
> >         case KVM_SET_USER_MEMORY_REGION: {
> > -               struct kvm_userspace_memory_region kvm_userspace_mem;
> > +               struct kvm_user_mem_region mem;
> > +               unsigned long size = sizeof(struct kvm_userspace_memory_region);
> > +
> > +               kvm_sanity_check_user_mem_region_alias();
> >
> >                 r = -EFAULT;
> > -               if (copy_from_user(&kvm_userspace_mem, argp,
> > -                                               sizeof(kvm_userspace_mem)))
> > +               if (copy_from_user(&mem, argp, size))
> > +                       goto out;
> > +
> > +               r = -EINVAL;
> > +               if (mem.flags & KVM_MEM_PRIVATE)
> >                         goto out;
> >
> > -               r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
> > +               r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> >                 break;
> >         }
> >         case KVM_GET_DIRTY_LOG: {
> > --
> > 2.25.1
> >

Re: [PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry

[Chao Peng]

On Mon, Dec 05, 2022 at 09:23:49AM +0000, Fuad Tabba wrote:
> Hi Chao,
> 
> On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > Currently in mmu_notifier invalidate path, hva range is recorded and
> > then checked against by mmu_notifier_retry_hva() in the page fault
> > handling path. However, for the to be introduced private memory, a page
> > fault may not have a hva associated, checking gfn(gpa) makes more sense.
> >
> > For existing hva based shared memory, gfn is expected to also work. The
> > only downside is when aliasing multiple gfns to a single hva, the
> > current algorithm of checking multiple ranges could result in a much
> > larger range being rejected. Such aliasing should be uncommon, so the
> > impact is expected small.
> >
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  arch/x86/kvm/mmu/mmu.c   |  8 +++++---
> >  include/linux/kvm_host.h | 33 +++++++++++++++++++++------------
> >  virt/kvm/kvm_main.c      | 32 +++++++++++++++++++++++---------
> >  3 files changed, 49 insertions(+), 24 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 4736d7849c60..e2c70b5afa3e 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4259,7 +4259,7 @@ static bool is_page_fault_stale(struct kvm_vcpu *vcpu,
> >                 return true;
> >
> >         return fault->slot &&
> > -              mmu_invalidate_retry_hva(vcpu->kvm, mmu_seq, fault->hva);
> > +              mmu_invalidate_retry_gfn(vcpu->kvm, mmu_seq, fault->gfn);
> >  }
> >
> >  static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > @@ -6098,7 +6098,9 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
> >
> >         write_lock(&kvm->mmu_lock);
> >
> > -       kvm_mmu_invalidate_begin(kvm, gfn_start, gfn_end);
> > +       kvm_mmu_invalidate_begin(kvm);
> > +
> > +       kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
> >
> >         flush = kvm_rmap_zap_gfn_range(kvm, gfn_start, gfn_end);
> >
> > @@ -6112,7 +6114,7 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
> >                 kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
> >                                                    gfn_end - gfn_start);
> >
> > -       kvm_mmu_invalidate_end(kvm, gfn_start, gfn_end);
> > +       kvm_mmu_invalidate_end(kvm);
> >
> >         write_unlock(&kvm->mmu_lock);
> >  }
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 02347e386ea2..3d69484d2704 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -787,8 +787,8 @@ struct kvm {
> >         struct mmu_notifier mmu_notifier;
> >         unsigned long mmu_invalidate_seq;
> >         long mmu_invalidate_in_progress;
> > -       unsigned long mmu_invalidate_range_start;
> > -       unsigned long mmu_invalidate_range_end;
> > +       gfn_t mmu_invalidate_range_start;
> > +       gfn_t mmu_invalidate_range_end;
> >  #endif
> >         struct list_head devices;
> >         u64 manual_dirty_log_protect;
> > @@ -1389,10 +1389,9 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
> >  void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> >  #endif
> >
> > -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> > -                             unsigned long end);
> > -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> > -                           unsigned long end);
> > +void kvm_mmu_invalidate_begin(struct kvm *kvm);
> > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end);
> > +void kvm_mmu_invalidate_end(struct kvm *kvm);
> >
> >  long kvm_arch_dev_ioctl(struct file *filp,
> >                         unsigned int ioctl, unsigned long arg);
> > @@ -1963,9 +1962,9 @@ static inline int mmu_invalidate_retry(struct kvm *kvm, unsigned long mmu_seq)
> >         return 0;
> >  }
> >
> > -static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
> > +static inline int mmu_invalidate_retry_gfn(struct kvm *kvm,
> >                                            unsigned long mmu_seq,
> > -                                          unsigned long hva)
> > +                                          gfn_t gfn)
> >  {
> >         lockdep_assert_held(&kvm->mmu_lock);
> >         /*
> > @@ -1974,10 +1973,20 @@ static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
> >          * that might be being invalidated. Note that it may include some false
> 
> nit: "might be" (or) "is being"
> 
> >          * positives, due to shortcuts when handing concurrent invalidations.
> 
> nit: handling

Both are existing code, but I can fix it either.

> 
> >          */
> > -       if (unlikely(kvm->mmu_invalidate_in_progress) &&
> > -           hva >= kvm->mmu_invalidate_range_start &&
> > -           hva < kvm->mmu_invalidate_range_end)
> > -               return 1;
> > +       if (unlikely(kvm->mmu_invalidate_in_progress)) {
> > +               /*
> > +                * Dropping mmu_lock after bumping mmu_invalidate_in_progress
> > +                * but before updating the range is a KVM bug.
> > +                */
> > +               if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
> > +                                kvm->mmu_invalidate_range_end == INVALID_GPA))
> 
> INVALID_GPA is an x86-specific define in
> arch/x86/include/asm/kvm_host.h, so this doesn't build on other
> architectures. The obvious fix is to move it to
> include/linux/kvm_host.h.

Hmm, INVALID_GPA is defined as ZERO for x86, not 100% confident this is
correct choice for other architectures, but after search it has not been
used for other architectures, so should be safe to make it common.

Thanks,
Chao
> 
> Cheers,
> /fuad
> 
> > +                       return 1;
> > +
> > +               if (gfn >= kvm->mmu_invalidate_range_start &&
> > +                   gfn < kvm->mmu_invalidate_range_end)
> > +                       return 1;
> > +       }
> > +
> >         if (kvm->mmu_invalidate_seq != mmu_seq)
> >                 return 1;
> >         return 0;
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index b882eb2c76a2..ad55dfbc75d7 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -540,9 +540,7 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,
> >
> >  typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
> >
> > -typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
> > -                            unsigned long end);
> > -
> > +typedef void (*on_lock_fn_t)(struct kvm *kvm);
> >  typedef void (*on_unlock_fn_t)(struct kvm *kvm);
> >
> >  struct kvm_hva_range {
> > @@ -628,7 +626,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
> >                                 locked = true;
> >                                 KVM_MMU_LOCK(kvm);
> >                                 if (!IS_KVM_NULL_FN(range->on_lock))
> > -                                       range->on_lock(kvm, range->start, range->end);
> > +                                       range->on_lock(kvm);
> > +
> >                                 if (IS_KVM_NULL_FN(range->handler))
> >                                         break;
> >                         }
> > @@ -715,8 +714,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> >         kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> >  }
> >
> > -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> > -                             unsigned long end)
> > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> >  {
> >         /*
> >          * The count increase must become visible at unlock time as no
> > @@ -724,6 +722,17 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> >          * count is also read inside the mmu_lock critical section.
> >          */
> >         kvm->mmu_invalidate_in_progress++;
> > +
> > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > +               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > +               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > +       }
> > +}
> > +
> > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > +{
> > +       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > +
> >         if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> >                 kvm->mmu_invalidate_range_start = start;
> >                 kvm->mmu_invalidate_range_end = end;
> > @@ -744,6 +753,12 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> >         }
> >  }
> >
> > +static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> > +{
> > +       kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > +       return kvm_unmap_gfn_range(kvm, range);
> > +}
> > +
> >  static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> >                                         const struct mmu_notifier_range *range)
> >  {
> > @@ -752,7 +767,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> >                 .start          = range->start,
> >                 .end            = range->end,
> >                 .pte            = __pte(0),
> > -               .handler        = kvm_unmap_gfn_range,
> > +               .handler        = kvm_mmu_unmap_gfn_range,
> >                 .on_lock        = kvm_mmu_invalidate_begin,
> >                 .on_unlock      = kvm_arch_guest_memory_reclaimed,
> >                 .flush_on_ret   = true,
> > @@ -791,8 +806,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> >         return 0;
> >  }
> >
> > -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> > -                           unsigned long end)
> > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> >  {
> >         /*
> >          * This sequence increase will notify the kvm page fault that
> > --
> > 2.25.1
> >

Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Chao Peng]

On Mon, Dec 05, 2022 at 02:49:59PM -0800, Isaku Yamahata wrote:
> On Fri, Dec 02, 2022 at 02:13:45PM +0800,
> Chao Peng <chao.p.peng@linux.intel.com> wrote:
> 
> > A large page with mixed private/shared subpages can't be mapped as large
> > page since its sub private/shared pages are from different memory
> > backends and may also treated by architecture differently. When
> > private/shared memory are mixed in a large page, the current lpage_info
> > is not sufficient to decide whether the page can be mapped as large page
> > or not and additional private/shared mixed information is needed.
> > 
> > Tracking this 'mixed' information with the current 'count' like
> > disallow_lpage is a bit challenge so reserve a bit in 'disallow_lpage'
> > to indicate a large page has mixed private/share subpages and update
> > this 'mixed' bit whenever the memory attribute is changed between
> > private and shared.
> > 
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |   8 ++
> >  arch/x86/kvm/mmu/mmu.c          | 134 +++++++++++++++++++++++++++++++-
> >  arch/x86/kvm/x86.c              |   2 +
> >  include/linux/kvm_host.h        |  19 +++++
> >  virt/kvm/kvm_main.c             |   9 ++-
> >  5 files changed, 169 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 283cbb83d6ae..7772ab37ac89 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -38,6 +38,7 @@
> >  #include <asm/hyperv-tlfs.h>
> >  
> >  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
> > +#define __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
> >  
> >  #define KVM_MAX_VCPUS 1024
> >  
> > @@ -1011,6 +1012,13 @@ struct kvm_vcpu_arch {
> >  #endif
> >  };
> >  
> > +/*
> > + * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
> > + * level. The remaining bits are used as a reference count.
> > + */
> > +#define KVM_LPAGE_PRIVATE_SHARED_MIXED		(1U << 31)
> > +#define KVM_LPAGE_COUNT_MAX			((1U << 31) - 1)
> > +
> >  struct kvm_lpage_info {
> >  	int disallow_lpage;
> >  };
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index e2c70b5afa3e..2190fd8c95c0 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -763,11 +763,16 @@ static void update_gfn_disallow_lpage_count(const struct kvm_memory_slot *slot,
> >  {
> >  	struct kvm_lpage_info *linfo;
> >  	int i;
> > +	int disallow_count;
> >  
> >  	for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
> >  		linfo = lpage_info_slot(gfn, slot, i);
> > +
> > +		disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
> > +		WARN_ON(disallow_count + count < 0 ||
> > +			disallow_count > KVM_LPAGE_COUNT_MAX - count);
> > +
> >  		linfo->disallow_lpage += count;
> > -		WARN_ON(linfo->disallow_lpage < 0);
> >  	}
> >  }
> >  
> > @@ -6986,3 +6991,130 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
> >  	if (kvm->arch.nx_huge_page_recovery_thread)
> >  		kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
> >  }
> > +
> > +static bool linfo_is_mixed(struct kvm_lpage_info *linfo)
> > +{
> > +	return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > +}
> > +
> > +static void linfo_set_mixed(gfn_t gfn, struct kvm_memory_slot *slot,
> > +			    int level, bool mixed)
> > +{
> > +	struct kvm_lpage_info *linfo = lpage_info_slot(gfn, slot, level);
> > +
> > +	if (mixed)
> > +		linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > +	else
> > +		linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > +}
> > +
> > +static bool is_expected_attr_entry(void *entry, unsigned long expected_attrs)
> > +{
> > +	bool expect_private = expected_attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > +
> > +	if (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) {
> > +		if (!expect_private)
> > +			return false;
> > +	} else if (expect_private)
> > +		return false;
> > +
> > +	return true;
> > +}
> > +
> > +static bool mem_attrs_mixed_2m(struct kvm *kvm, unsigned long attrs,
> > +			       gfn_t start, gfn_t end)
> > +{
> > +	XA_STATE(xas, &kvm->mem_attr_array, start);
> > +	gfn_t gfn = start;
> > +	void *entry;
> > +	bool mixed = false;
> > +
> > +	rcu_read_lock();
> > +	entry = xas_load(&xas);
> > +	while (gfn < end) {
> > +		if (xas_retry(&xas, entry))
> > +			continue;
> > +
> > +		KVM_BUG_ON(gfn != xas.xa_index, kvm);
> > +
> > +		if (!is_expected_attr_entry(entry, attrs)) {
> > +			mixed = true;
> > +			break;
> > +		}
> > +
> > +		entry = xas_next(&xas);
> > +		gfn++;
> > +	}
> > +
> > +	rcu_read_unlock();
> > +	return mixed;
> > +}
> > +
> > +static bool mem_attrs_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
> > +			    int level, unsigned long attrs,
> > +			    gfn_t start, gfn_t end)
> > +{
> > +	unsigned long gfn;
> > +
> > +	if (level == PG_LEVEL_2M)
> > +		return mem_attrs_mixed_2m(kvm, attrs, start, end);
> > +
> > +	for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1))
> > +		if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
> > +		    !is_expected_attr_entry(xa_load(&kvm->mem_attr_array, gfn),
> > +					    attrs))
> > +			return true;
> > +	return false;
> > +}
> > +
> > +static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
> > +						  struct kvm_memory_slot *slot,
> > +						  unsigned long attrs,
> > +						  gfn_t start, gfn_t end)
> > +{
> > +	unsigned long pages, mask;
> > +	gfn_t gfn, gfn_end, first, last;
> > +	int level;
> > +	bool mixed;
> > +
> > +	/*
> > +	 * The sequence matters here: we set the higher level basing on the
> > +	 * lower level's scanning result.
> > +	 */
> > +	for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> > +		pages = KVM_PAGES_PER_HPAGE(level);
> > +		mask = ~(pages - 1);
> > +		first = start & mask;
> > +		last = (end - 1) & mask;
> > +
> > +		/*
> > +		 * We only need to scan the head and tail page, for middle pages
> > +		 * we know they will not be mixed.
> > +		 */
> > +		gfn = max(first, slot->base_gfn);
> > +		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
> > +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> > +		linfo_set_mixed(gfn, slot, level, mixed);
> > +
> > +		if (first == last)
> > +			return;
> 
> 
> continue.

Ya!

> 
> > +
> > +		for (gfn = first + pages; gfn < last; gfn += pages)
> > +			linfo_set_mixed(gfn, slot, level, false);
> > +
> > +		gfn = last;
> > +		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
> 
> if (gfn == gfn_end) continue.

Do you see a case where gfn can equal to gfn_end? Though it does not
hurt to add a check.

> 
> 
> > +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> > +		linfo_set_mixed(gfn, slot, level, mixed);
> > +	}
> > +}
> > +
> > +void kvm_arch_set_memory_attributes(struct kvm *kvm,
> > +				    struct kvm_memory_slot *slot,
> > +				    unsigned long attrs,
> > +				    gfn_t start, gfn_t end)
> > +{
> > +	if (kvm_slot_can_be_private(slot))
> > +		kvm_update_lpage_private_shared_mixed(kvm, slot, attrs,
> > +						      start, end);
> > +}
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 9a07380f8d3c..5aefcff614d2 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
> >  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
> >  			linfo[lpages - 1].disallow_lpage = 1;
> >  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> > +		if (kvm_slot_can_be_private(slot))
> > +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
> 
> Is there any alignment restriction? If no, It should be +=.
> In practice, alignment will hold though.

All we need here is checking whether both userspace_addr and
restricted_offset are aligned to HPAGE_SIZE or not. '+=' actually can
yield wrong value in cases when userspace_addr + restricted_offset is
aligned to HPAGE_SIZE but individually they may not align to HPAGE_SIZE.

Thanks,
Chao
> 
> Thanks,
> 
> >  		/*
> >  		 * If the gfn and userspace address are not aligned wrt each
> >  		 * other, disable large page support for this slot.
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 3331c0c92838..25099c94e770 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -592,6 +592,11 @@ struct kvm_memory_slot {
> >  	struct restrictedmem_notifier notifier;
> >  };
> >  
> > +static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
> > +{
> > +	return slot && (slot->flags & KVM_MEM_PRIVATE);
> > +}
> > +
> >  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
> >  {
> >  	return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
> > @@ -2316,4 +2321,18 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
> >  /* Max number of entries allowed for each kvm dirty ring */
> >  #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
> >  
> > +#ifdef __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
> > +void kvm_arch_set_memory_attributes(struct kvm *kvm,
> > +				    struct kvm_memory_slot *slot,
> > +				    unsigned long attrs,
> > +				    gfn_t start, gfn_t end);
> > +#else
> > +static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> > +						  struct kvm_memory_slot *slot,
> > +						  unsigned long attrs,
> > +						  gfn_t start, gfn_t end)
> > +{
> > +}
> > +#endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
> > +
> >  #endif
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 4e1e1e113bf0..e107afea32f0 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2354,7 +2354,8 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> >  	return 0;
> >  }
> >  
> > -static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> > +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end,
> > +				unsigned long attrs)
> >  {
> >  	struct kvm_gfn_range gfn_range;
> >  	struct kvm_memory_slot *slot;
> > @@ -2378,6 +2379,10 @@ static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> >  			gfn_range.slot = slot;
> >  
> >  			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> > +
> > +			kvm_arch_set_memory_attributes(kvm, slot, attrs,
> > +						       gfn_range.start,
> > +						       gfn_range.end);
> >  		}
> >  	}
> >  
> > @@ -2427,7 +2432,7 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> >  		idx = srcu_read_lock(&kvm->srcu);
> >  		KVM_MMU_LOCK(kvm);
> >  		if (i > start)
> > -			kvm_unmap_mem_range(kvm, start, i);
> > +			kvm_unmap_mem_range(kvm, start, i, attrs->attributes);
> >  		kvm_mmu_invalidate_end(kvm);
> >  		KVM_MMU_UNLOCK(kvm);
> >  		srcu_read_unlock(&kvm->srcu, idx);
> > -- 
> > 2.25.1
> > 
> 
> -- 
> Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Fuad Tabba]

Hi Chao,

On Tue, Dec 6, 2022 at 11:58 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> On Mon, Dec 05, 2022 at 09:03:11AM +0000, Fuad Tabba wrote:
> > Hi Chao,
> >
> > On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > >
> > > In memory encryption usage, guest memory may be encrypted with special
> > > key and can be accessed only by the guest itself. We call such memory
> > > private memory. It's valueless and sometimes can cause problem to allow
> > > userspace to access guest private memory. This new KVM memslot extension
> > > allows guest private memory being provided through a restrictedmem
> > > backed file descriptor(fd) and userspace is restricted to access the
> > > bookmarked memory in the fd.
> > >
> > > This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> > > additional KVM memslot fields restricted_fd/restricted_offset to allow
> > > userspace to instruct KVM to provide guest memory through restricted_fd.
> > > 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> > > and the size is 'memory_size'.
> > >
> > > The extended memslot can still have the userspace_addr(hva). When use, a
> > > single memslot can maintain both private memory through restricted_fd
> > > and shared memory through userspace_addr. Whether the private or shared
> > > part is visible to guest is maintained by other KVM code.
> > >
> > > A restrictedmem_notifier field is also added to the memslot structure to
> > > allow the restricted_fd's backing store to notify KVM the memory change,
> > > KVM then can invalidate its page table entries or handle memory errors.
> > >
> > > Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> > > and right now it is selected on X86_64 only.
> > >
> > > To make future maintenance easy, internally use a binary compatible
> > > alias struct kvm_user_mem_region to handle both the normal and the
> > > '_ext' variants.
> > >
> > > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > Reviewed-by: Fuad Tabba <tabba@google.com>
> > > Tested-by: Fuad Tabba <tabba@google.com>
> >
> > V9 of this patch [*] had KVM_CAP_PRIVATE_MEM, but it's not in this
> > patch series anymore. Any reason you removed it, or is it just an
> > omission?
>
> We had some discussion in v9 [1] to add generic memory attributes ioctls
> and KVM_CAP_PRIVATE_MEM can be implemented as a new
> KVM_MEMORY_ATTRIBUTE_PRIVATE flag via KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES()
> ioctl [2]. The api doc has been updated:
>
> +- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
> +  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl) …
>
>
> [1] https://lore.kernel.org/linux-mm/Y2WB48kD0J4VGynX@google.com/
> [2]
> https://lore.kernel.org/linux-mm/20221202061347.1070246-3-chao.p.peng@linux.intel.com/

I see. I just retested it with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES,
and my Reviewed/Tested-by still apply.

Cheers,
/fuad

>
> Thanks,
> Chao
> >
> > [*] https://lore.kernel.org/linux-mm/20221025151344.3784230-3-chao.p.peng@linux.intel.com/
> >
> > Thanks,
> > /fuad
> >
> > > ---
> > >  Documentation/virt/kvm/api.rst | 40 ++++++++++++++++++++++-----
> > >  arch/x86/kvm/Kconfig           |  2 ++
> > >  arch/x86/kvm/x86.c             |  2 +-
> > >  include/linux/kvm_host.h       |  8 ++++--
> > >  include/uapi/linux/kvm.h       | 28 +++++++++++++++++++
> > >  virt/kvm/Kconfig               |  3 +++
> > >  virt/kvm/kvm_main.c            | 49 ++++++++++++++++++++++++++++------
> > >  7 files changed, 114 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > > index bb2f709c0900..99352170c130 100644
> > > --- a/Documentation/virt/kvm/api.rst
> > > +++ b/Documentation/virt/kvm/api.rst
> > > @@ -1319,7 +1319,7 @@ yet and must be cleared on entry.
> > >  :Capability: KVM_CAP_USER_MEMORY
> > >  :Architectures: all
> > >  :Type: vm ioctl
> > > -:Parameters: struct kvm_userspace_memory_region (in)
> > > +:Parameters: struct kvm_userspace_memory_region(_ext) (in)
> > >  :Returns: 0 on success, -1 on error
> > >
> > >  ::
> > > @@ -1332,9 +1332,18 @@ yet and must be cleared on entry.
> > >         __u64 userspace_addr; /* start of the userspace allocated memory */
> > >    };
> > >
> > > +  struct kvm_userspace_memory_region_ext {
> > > +       struct kvm_userspace_memory_region region;
> > > +       __u64 restricted_offset;
> > > +       __u32 restricted_fd;
> > > +       __u32 pad1;
> > > +       __u64 pad2[14];
> > > +  };
> > > +
> > >    /* for kvm_memory_region::flags */
> > >    #define KVM_MEM_LOG_DIRTY_PAGES      (1UL << 0)
> > >    #define KVM_MEM_READONLY     (1UL << 1)
> > > +  #define KVM_MEM_PRIVATE              (1UL << 2)
> > >
> > >  This ioctl allows the user to create, modify or delete a guest physical
> > >  memory slot.  Bits 0-15 of "slot" specify the slot id and this value
> > > @@ -1365,12 +1374,29 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
> > >  be identical.  This allows large pages in the guest to be backed by large
> > >  pages in the host.
> > >
> > > -The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
> > > -KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
> > > -writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
> > > -use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
> > > -to make a new slot read-only.  In this case, writes to this memory will be
> > > -posted to userspace as KVM_EXIT_MMIO exits.
> > > +kvm_userspace_memory_region_ext struct includes all fields of
> > > +kvm_userspace_memory_region struct, while also adds additional fields for some
> > > +other features. See below description of flags field for more information.
> > > +It's recommended to use kvm_userspace_memory_region_ext in new userspace code.
> > > +
> > > +The flags field supports following flags:
> > > +
> > > +- KVM_MEM_LOG_DIRTY_PAGES to instruct KVM to keep track of writes to memory
> > > +  within the slot. For more details, see KVM_GET_DIRTY_LOG ioctl.
> > > +
> > > +- KVM_MEM_READONLY, if KVM_CAP_READONLY_MEM allows, to make a new slot
> > > +  read-only. In this case, writes to this memory will be posted to userspace as
> > > +  KVM_EXIT_MMIO exits.
> > > +
> > > +- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
> > > +  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl), to indicate a new slot has private
> > > +  memory backed by a file descriptor(fd) and userspace access to the fd may be
> > > +  restricted. Userspace should use restricted_fd/restricted_offset in the
> > > +  kvm_userspace_memory_region_ext to instruct KVM to provide private memory
> > > +  to guest. Userspace should guarantee not to map the same host physical address
> > > +  indicated by restricted_fd/restricted_offset to different guest physical
> > > +  addresses within multiple memslots. Failed to do this may result undefined
> > > +  behavior.
> > >
> > >  When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
> > >  the memory region are automatically reflected into the guest.  For example, an
> > > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > > index a8e379a3afee..690cb21010e7 100644
> > > --- a/arch/x86/kvm/Kconfig
> > > +++ b/arch/x86/kvm/Kconfig
> > > @@ -50,6 +50,8 @@ config KVM
> > >         select INTERVAL_TREE
> > >         select HAVE_KVM_PM_NOTIFIER if PM
> > >         select HAVE_KVM_MEMORY_ATTRIBUTES
> > > +       select HAVE_KVM_RESTRICTED_MEM if X86_64
> > > +       select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
> > >         help
> > >           Support hosting fully virtualized guest machines using hardware
> > >           virtualization extensions.  You will need a fairly recent
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index 7f850dfb4086..9a07380f8d3c 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -12224,7 +12224,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
> > >         }
> > >
> > >         for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > > -               struct kvm_userspace_memory_region m;
> > > +               struct kvm_user_mem_region m;
> > >
> > >                 m.slot = id | (i << 16);
> > >                 m.flags = 0;
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index a784e2b06625..02347e386ea2 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -44,6 +44,7 @@
> > >
> > >  #include <asm/kvm_host.h>
> > >  #include <linux/kvm_dirty_ring.h>
> > > +#include <linux/restrictedmem.h>
> > >
> > >  #ifndef KVM_MAX_VCPU_IDS
> > >  #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
> > > @@ -585,6 +586,9 @@ struct kvm_memory_slot {
> > >         u32 flags;
> > >         short id;
> > >         u16 as_id;
> > > +       struct file *restricted_file;
> > > +       loff_t restricted_offset;
> > > +       struct restrictedmem_notifier notifier;
> > >  };
> > >
> > >  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
> > > @@ -1123,9 +1127,9 @@ enum kvm_mr_change {
> > >  };
> > >
> > >  int kvm_set_memory_region(struct kvm *kvm,
> > > -                         const struct kvm_userspace_memory_region *mem);
> > > +                         const struct kvm_user_mem_region *mem);
> > >  int __kvm_set_memory_region(struct kvm *kvm,
> > > -                           const struct kvm_userspace_memory_region *mem);
> > > +                           const struct kvm_user_mem_region *mem);
> > >  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
> > >  void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
> > >  int kvm_arch_prepare_memory_region(struct kvm *kvm,
> > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > > index 5d0941acb5bb..13bff963b8b0 100644
> > > --- a/include/uapi/linux/kvm.h
> > > +++ b/include/uapi/linux/kvm.h
> > > @@ -103,6 +103,33 @@ struct kvm_userspace_memory_region {
> > >         __u64 userspace_addr; /* start of the userspace allocated memory */
> > >  };
> > >
> > > +struct kvm_userspace_memory_region_ext {
> > > +       struct kvm_userspace_memory_region region;
> > > +       __u64 restricted_offset;
> > > +       __u32 restricted_fd;
> > > +       __u32 pad1;
> > > +       __u64 pad2[14];
> > > +};
> > > +
> > > +#ifdef __KERNEL__
> > > +/*
> > > + * kvm_user_mem_region is a kernel-only alias of kvm_userspace_memory_region_ext
> > > + * that "unpacks" kvm_userspace_memory_region so that KVM can directly access
> > > + * all fields from the top-level "extended" region.
> > > + */
> > > +struct kvm_user_mem_region {
> > > +       __u32 slot;
> > > +       __u32 flags;
> > > +       __u64 guest_phys_addr;
> > > +       __u64 memory_size;
> > > +       __u64 userspace_addr;
> > > +       __u64 restricted_offset;
> > > +       __u32 restricted_fd;
> > > +       __u32 pad1;
> > > +       __u64 pad2[14];
> > > +};
> > > +#endif
> > > +
> > >  /*
> > >   * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
> > >   * other bits are reserved for kvm internal use which are defined in
> > > @@ -110,6 +137,7 @@ struct kvm_userspace_memory_region {
> > >   */
> > >  #define KVM_MEM_LOG_DIRTY_PAGES        (1UL << 0)
> > >  #define KVM_MEM_READONLY       (1UL << 1)
> > > +#define KVM_MEM_PRIVATE                (1UL << 2)
> > >
> > >  /* for KVM_IRQ_LINE */
> > >  struct kvm_irq_level {
> > > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> > > index effdea5dd4f0..d605545d6dd1 100644
> > > --- a/virt/kvm/Kconfig
> > > +++ b/virt/kvm/Kconfig
> > > @@ -89,3 +89,6 @@ config KVM_XFER_TO_GUEST_WORK
> > >
> > >  config HAVE_KVM_PM_NOTIFIER
> > >         bool
> > > +
> > > +config HAVE_KVM_RESTRICTED_MEM
> > > +       bool
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index 7f0f5e9f2406..b882eb2c76a2 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -1532,7 +1532,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
> > >         }
> > >  }
> > >
> > > -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
> > > +static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> > >  {
> > >         u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> > >
> > > @@ -1934,7 +1934,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
> > >   * Must be called holding kvm->slots_lock for write.
> > >   */
> > >  int __kvm_set_memory_region(struct kvm *kvm,
> > > -                           const struct kvm_userspace_memory_region *mem)
> > > +                           const struct kvm_user_mem_region *mem)
> > >  {
> > >         struct kvm_memory_slot *old, *new;
> > >         struct kvm_memslots *slots;
> > > @@ -2038,7 +2038,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > >  EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> > >
> > >  int kvm_set_memory_region(struct kvm *kvm,
> > > -                         const struct kvm_userspace_memory_region *mem)
> > > +                         const struct kvm_user_mem_region *mem)
> > >  {
> > >         int r;
> > >
> > > @@ -2050,7 +2050,7 @@ int kvm_set_memory_region(struct kvm *kvm,
> > >  EXPORT_SYMBOL_GPL(kvm_set_memory_region);
> > >
> > >  static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
> > > -                                         struct kvm_userspace_memory_region *mem)
> > > +                                         struct kvm_user_mem_region *mem)
> > >  {
> > >         if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
> > >                 return -EINVAL;
> > > @@ -4698,6 +4698,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
> > >         return fd;
> > >  }
> > >
> > > +#define SANITY_CHECK_MEM_REGION_FIELD(field)                                   \
> > > +do {                                                                           \
> > > +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=             \
> > > +                    offsetof(struct kvm_userspace_memory_region, field));      \
> > > +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=         \
> > > +                    sizeof_field(struct kvm_userspace_memory_region, field));  \
> > > +} while (0)
> > > +
> > > +#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)                                       \
> > > +do {                                                                                   \
> > > +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=                     \
> > > +                    offsetof(struct kvm_userspace_memory_region_ext, field));          \
> > > +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=                 \
> > > +                    sizeof_field(struct kvm_userspace_memory_region_ext, field));      \
> > > +} while (0)
> > > +
> > > +static void kvm_sanity_check_user_mem_region_alias(void)
> > > +{
> > > +       SANITY_CHECK_MEM_REGION_FIELD(slot);
> > > +       SANITY_CHECK_MEM_REGION_FIELD(flags);
> > > +       SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
> > > +       SANITY_CHECK_MEM_REGION_FIELD(memory_size);
> > > +       SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
> > > +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_offset);
> > > +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_fd);
> > > +}
> > > +
> > >  static long kvm_vm_ioctl(struct file *filp,
> > >                            unsigned int ioctl, unsigned long arg)
> > >  {
> > > @@ -4721,14 +4748,20 @@ static long kvm_vm_ioctl(struct file *filp,
> > >                 break;
> > >         }
> > >         case KVM_SET_USER_MEMORY_REGION: {
> > > -               struct kvm_userspace_memory_region kvm_userspace_mem;
> > > +               struct kvm_user_mem_region mem;
> > > +               unsigned long size = sizeof(struct kvm_userspace_memory_region);
> > > +
> > > +               kvm_sanity_check_user_mem_region_alias();
> > >
> > >                 r = -EFAULT;
> > > -               if (copy_from_user(&kvm_userspace_mem, argp,
> > > -                                               sizeof(kvm_userspace_mem)))
> > > +               if (copy_from_user(&mem, argp, size))
> > > +                       goto out;
> > > +
> > > +               r = -EINVAL;
> > > +               if (mem.flags & KVM_MEM_PRIVATE)
> > >                         goto out;
> > >
> > > -               r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
> > > +               r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> > >                 break;
> > >         }
> > >         case KVM_GET_DIRTY_LOG: {
> > > --
> > > 2.25.1
> > >

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Fabiano Rosas]

Chao Peng <chao.p.peng@linux.intel.com> writes:

> In confidential computing usages, whether a page is private or shared is
> necessary information for KVM to perform operations like page fault
> handling, page zapping etc. There are other potential use cases for
> per-page memory attributes, e.g. to make memory read-only (or no-exec,
> or exec-only, etc.) without having to modify memslots.
>
> Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> userspace to operate on the per-page memory attributes.
>   - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
>     a guest memory range.
>   - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
>     memory attributes.
>
> KVM internally uses xarray to store the per-page memory attributes.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> ---
>  Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
>  arch/x86/kvm/Kconfig           |  1 +
>  include/linux/kvm_host.h       |  3 ++
>  include/uapi/linux/kvm.h       | 17 ++++++++
>  virt/kvm/Kconfig               |  3 ++
>  virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
>  6 files changed, 163 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 5617bc4f899f..bb2f709c0900 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
>  The "pad" and "reserved" fields may be used for future extensions and should be
>  set to 0s by userspace.
>  
> +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: u64 memory attributes bitmask(out)
> +:Returns: 0 on success, <0 on error
> +
> +Returns supported memory attributes bitmask. Supported memory attributes will
> +have the corresponding bits set in u64 memory attributes bitmask.
> +
> +The following memory attributes are defined::
> +
> +  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> +
> +4.139 KVM_SET_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: struct kvm_memory_attributes(in/out)
> +:Returns: 0 on success, <0 on error
> +
> +Sets memory attributes for pages in a guest memory range. Parameters are
> +specified via the following structure::
> +
> +  struct kvm_memory_attributes {
> +	__u64 address;
> +	__u64 size;
> +	__u64 attributes;
> +	__u64 flags;
> +  };
> +
> +The user sets the per-page memory attributes to a guest memory range indicated
> +by address/size, and in return KVM adjusts address and size to reflect the
> +actual pages of the memory range have been successfully set to the attributes.

This wording could cause some confusion, what about a simpler:

"reflect the range of pages that had its attributes successfully set"

> +If the call returns 0, "address" is updated to the last successful address + 1
> +and "size" is updated to the remaining address size that has not been set
> +successfully.

"address + 1 page" or "subsequent page" perhaps.

In fact, wouldn't this all become simpler if size were number of pages instead?

> The user should check the return value as well as the size to
> +decide if the operation succeeded for the whole range or not. The user may want
> +to retry the operation with the returned address/size if the previous range was
> +partially successful.
> +
> +Both address and size should be page aligned and the supported attributes can be
> +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> +
> +The "flags" field may be used for future extensions and should be set to 0s.
> +

...

> +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> +					   struct kvm_memory_attributes *attrs)
> +{
> +	gfn_t start, end;
> +	unsigned long i;
> +	void *entry;
> +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> +
> +	/* flags is currently not used. */
> +	if (attrs->flags)
> +		return -EINVAL;
> +	if (attrs->attributes & ~supported_attrs)
> +		return -EINVAL;
> +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> +		return -EINVAL;
> +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> +		return -EINVAL;
> +
> +	start = attrs->address >> PAGE_SHIFT;
> +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;

Here PAGE_SIZE and -1 cancel out.

Consider using gpa_to_gfn as well.

> +
> +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> +
> +	mutex_lock(&kvm->lock);
> +	for (i = start; i < end; i++)
> +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> +				    GFP_KERNEL_ACCOUNT)))
> +			break;
> +	mutex_unlock(&kvm->lock);
> +
> +	attrs->address = i << PAGE_SHIFT;
> +	attrs->size = (end - i) << PAGE_SHIFT;
> +
> +	return 0;
> +}
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +
>  struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
>  {
>  	return __gfn_to_memslot(kvm_memslots(kvm), gfn);
> @@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>  #ifdef CONFIG_HAVE_KVM_MSI
>  	case KVM_CAP_SIGNAL_MSI:
>  #endif
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	case KVM_CAP_MEMORY_ATTRIBUTES:
> +#endif
>  #ifdef CONFIG_HAVE_KVM_IRQFD
>  	case KVM_CAP_IRQFD:
>  	case KVM_CAP_IRQFD_RESAMPLE:
> @@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp,
>  		break;
>  	}
>  #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: {
> +		u64 attrs = kvm_supported_mem_attributes(kvm);
> +
> +		r = -EFAULT;
> +		if (copy_to_user(argp, &attrs, sizeof(attrs)))
> +			goto out;
> +		r = 0;
> +		break;
> +	}
> +	case KVM_SET_MEMORY_ATTRIBUTES: {
> +		struct kvm_memory_attributes attrs;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&attrs, argp, sizeof(attrs)))
> +			goto out;
> +
> +		r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);
> +
> +		if (!r && copy_to_user(argp, &attrs, sizeof(attrs)))
> +			r = -EFAULT;
> +		break;
> +	}
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
>  	case KVM_CREATE_DEVICE: {
>  		struct kvm_create_device cd;

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Fuad Tabba]

Hi,

On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> Introduce 'memfd_restricted' system call with the ability to create
> memory areas that are restricted from userspace access through ordinary
> MMU operations (e.g. read/write/mmap). The memory content is expected to
> be used through the new in-kernel interface by a third kernel module.
>
> memfd_restricted() is useful for scenarios where a file descriptor(fd)
> can be used as an interface into mm but want to restrict userspace's
> ability on the fd. Initially it is designed to provide protections for
> KVM encrypted guest memory.
>
> Normally KVM uses memfd memory via mmapping the memfd into KVM userspace
> (e.g. QEMU) and then using the mmaped virtual address to setup the
> mapping in the KVM secondary page table (e.g. EPT). With confidential
> computing technologies like Intel TDX, the memfd memory may be encrypted
> with special key for special software domain (e.g. KVM guest) and is not
> expected to be directly accessed by userspace. Precisely, userspace
> access to such encrypted memory may lead to host crash so should be
> prevented.
>
> memfd_restricted() provides semantics required for KVM guest encrypted
> memory support that a fd created with memfd_restricted() is going to be
> used as the source of guest memory in confidential computing environment
> and KVM can directly interact with core-mm without the need to expose
> the memoy content into KVM userspace.

nit: memory

>
> KVM userspace is still in charge of the lifecycle of the fd. It should
> pass the created fd to KVM. KVM uses the new restrictedmem_get_page() to
> obtain the physical memory page and then uses it to populate the KVM
> secondary page table entries.
>
> The userspace restricted memfd can be fallocate-ed or hole-punched
> from userspace. When hole-punched, KVM can get notified through
> invalidate_start/invalidate_end() callbacks, KVM then gets chance to
> remove any mapped entries of the range in the secondary page tables.
>
> Machine check can happen for memory pages in the restricted memfd,
> instead of routing this directly to userspace, we call the error()
> callback that KVM registered. KVM then gets chance to handle it
> correctly.
>
> memfd_restricted() itself is implemented as a shim layer on top of real
> memory file systems (currently tmpfs). Pages in restrictedmem are marked
> as unmovable and unevictable, this is required for current confidential
> usage. But in future this might be changed.
>
> By default memfd_restricted() prevents userspace read, write and mmap.
> By defining new bit in the 'flags', it can be extended to support other
> restricted semantics in the future.
>
> The system call is currently wired up for x86 arch.

Reviewed-by: Fuad Tabba <tabba@google.com>
After wiring the system call for arm64 (on qemu/arm64):
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad



>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  arch/x86/entry/syscalls/syscall_32.tbl |   1 +
>  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
>  include/linux/restrictedmem.h          |  71 ++++++
>  include/linux/syscalls.h               |   1 +
>  include/uapi/asm-generic/unistd.h      |   5 +-
>  include/uapi/linux/magic.h             |   1 +
>  kernel/sys_ni.c                        |   3 +
>  mm/Kconfig                             |   4 +
>  mm/Makefile                            |   1 +
>  mm/memory-failure.c                    |   3 +
>  mm/restrictedmem.c                     | 318 +++++++++++++++++++++++++
>  11 files changed, 408 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/restrictedmem.h
>  create mode 100644 mm/restrictedmem.c
>
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index 320480a8db4f..dc70ba90247e 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -455,3 +455,4 @@
>  448    i386    process_mrelease        sys_process_mrelease
>  449    i386    futex_waitv             sys_futex_waitv
>  450    i386    set_mempolicy_home_node         sys_set_mempolicy_home_node
> +451    i386    memfd_restricted        sys_memfd_restricted
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index c84d12608cd2..06516abc8318 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -372,6 +372,7 @@
>  448    common  process_mrelease        sys_process_mrelease
>  449    common  futex_waitv             sys_futex_waitv
>  450    common  set_mempolicy_home_node sys_set_mempolicy_home_node
> +451    common  memfd_restricted        sys_memfd_restricted
>
>  #
>  # Due to a historical design error, certain syscalls are numbered differently
> diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
> new file mode 100644
> index 000000000000..c2700c5daa43
> --- /dev/null
> +++ b/include/linux/restrictedmem.h
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _LINUX_RESTRICTEDMEM_H
> +
> +#include <linux/file.h>
> +#include <linux/magic.h>
> +#include <linux/pfn_t.h>
> +
> +struct restrictedmem_notifier;
> +
> +struct restrictedmem_notifier_ops {
> +       void (*invalidate_start)(struct restrictedmem_notifier *notifier,
> +                                pgoff_t start, pgoff_t end);
> +       void (*invalidate_end)(struct restrictedmem_notifier *notifier,
> +                              pgoff_t start, pgoff_t end);
> +       void (*error)(struct restrictedmem_notifier *notifier,
> +                              pgoff_t start, pgoff_t end);
> +};
> +
> +struct restrictedmem_notifier {
> +       struct list_head list;
> +       const struct restrictedmem_notifier_ops *ops;
> +};
> +
> +#ifdef CONFIG_RESTRICTEDMEM
> +
> +void restrictedmem_register_notifier(struct file *file,
> +                                    struct restrictedmem_notifier *notifier);
> +void restrictedmem_unregister_notifier(struct file *file,
> +                                      struct restrictedmem_notifier *notifier);
> +
> +int restrictedmem_get_page(struct file *file, pgoff_t offset,
> +                          struct page **pagep, int *order);
> +
> +static inline bool file_is_restrictedmem(struct file *file)
> +{
> +       return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC;
> +}
> +
> +void restrictedmem_error_page(struct page *page, struct address_space *mapping);
> +
> +#else
> +
> +static inline void restrictedmem_register_notifier(struct file *file,
> +                                    struct restrictedmem_notifier *notifier)
> +{
> +}
> +
> +static inline void restrictedmem_unregister_notifier(struct file *file,
> +                                      struct restrictedmem_notifier *notifier)
> +{
> +}
> +
> +static inline int restrictedmem_get_page(struct file *file, pgoff_t offset,
> +                                        struct page **pagep, int *order)
> +{
> +       return -1;
> +}
> +
> +static inline bool file_is_restrictedmem(struct file *file)
> +{
> +       return false;
> +}
> +
> +static inline void restrictedmem_error_page(struct page *page,
> +                                           struct address_space *mapping)
> +{
> +}
> +
> +#endif /* CONFIG_RESTRICTEDMEM */
> +
> +#endif /* _LINUX_RESTRICTEDMEM_H */
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index a34b0f9a9972..f9e9e0c820c5 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1056,6 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
>  asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
>                                             unsigned long home_node,
>                                             unsigned long flags);
> +asmlinkage long sys_memfd_restricted(unsigned int flags);
>
>  /*
>   * Architecture-specific system calls
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index 45fa180cc56a..e93cd35e46d0 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
>  #define __NR_set_mempolicy_home_node 450
>  __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
>
> +#define __NR_memfd_restricted 451
> +__SYSCALL(__NR_memfd_restricted, sys_memfd_restricted)
> +
>  #undef __NR_syscalls
> -#define __NR_syscalls 451
> +#define __NR_syscalls 452
>
>  /*
>   * 32 bit systems traditionally used different
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index 6325d1d0e90f..8aa38324b90a 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -101,5 +101,6 @@
>  #define DMA_BUF_MAGIC          0x444d4142      /* "DMAB" */
>  #define DEVMEM_MAGIC           0x454d444d      /* "DMEM" */
>  #define SECRETMEM_MAGIC                0x5345434d      /* "SECM" */
> +#define RESTRICTEDMEM_MAGIC    0x5245534d      /* "RESM" */
>
>  #endif /* __LINUX_MAGIC_H__ */
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 860b2dcf3ac4..7c4a32cbd2e7 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -360,6 +360,9 @@ COND_SYSCALL(pkey_free);
>  /* memfd_secret */
>  COND_SYSCALL(memfd_secret);
>
> +/* memfd_restricted */
> +COND_SYSCALL(memfd_restricted);
> +
>  /*
>   * Architecture specific weak syscall entries.
>   */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 57e1d8c5b505..06b0e1d6b8c1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1076,6 +1076,10 @@ config IO_MAPPING
>  config SECRETMEM
>         def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
>
> +config RESTRICTEDMEM
> +       bool
> +       depends on TMPFS
> +
>  config ANON_VMA_NAME
>         bool "Anonymous VMA name support"
>         depends on PROC_FS && ADVISE_SYSCALLS && MMU
> diff --git a/mm/Makefile b/mm/Makefile
> index 8e105e5b3e29..bcbb0edf9ba1 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -121,6 +121,7 @@ obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
>  obj-$(CONFIG_PAGE_TABLE_CHECK) += page_table_check.o
>  obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
>  obj-$(CONFIG_SECRETMEM) += secretmem.o
> +obj-$(CONFIG_RESTRICTEDMEM) += restrictedmem.o
>  obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o
>  obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
>  obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 145bb561ddb3..f91b444e471e 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -62,6 +62,7 @@
>  #include <linux/page-isolation.h>
>  #include <linux/pagewalk.h>
>  #include <linux/shmem_fs.h>
> +#include <linux/restrictedmem.h>
>  #include "swap.h"
>  #include "internal.h"
>  #include "ras/ras_event.h"
> @@ -940,6 +941,8 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
>                 goto out;
>         }
>
> +       restrictedmem_error_page(p, mapping);
> +
>         /*
>          * The shmem page is kept in page cache instead of truncating
>          * so is expected to have an extra refcount after error-handling.
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> new file mode 100644
> index 000000000000..56953c204e5c
> --- /dev/null
> +++ b/mm/restrictedmem.c
> @@ -0,0 +1,318 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "linux/sbitmap.h"
> +#include <linux/pagemap.h>
> +#include <linux/pseudo_fs.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/syscalls.h>
> +#include <uapi/linux/falloc.h>
> +#include <uapi/linux/magic.h>
> +#include <linux/restrictedmem.h>
> +
> +struct restrictedmem_data {
> +       struct mutex lock;
> +       struct file *memfd;
> +       struct list_head notifiers;
> +};
> +
> +static void restrictedmem_invalidate_start(struct restrictedmem_data *data,
> +                                          pgoff_t start, pgoff_t end)
> +{
> +       struct restrictedmem_notifier *notifier;
> +
> +       mutex_lock(&data->lock);
> +       list_for_each_entry(notifier, &data->notifiers, list) {
> +               notifier->ops->invalidate_start(notifier, start, end);
> +       }
> +       mutex_unlock(&data->lock);
> +}
> +
> +static void restrictedmem_invalidate_end(struct restrictedmem_data *data,
> +                                        pgoff_t start, pgoff_t end)
> +{
> +       struct restrictedmem_notifier *notifier;
> +
> +       mutex_lock(&data->lock);
> +       list_for_each_entry(notifier, &data->notifiers, list) {
> +               notifier->ops->invalidate_end(notifier, start, end);
> +       }
> +       mutex_unlock(&data->lock);
> +}
> +
> +static void restrictedmem_notifier_error(struct restrictedmem_data *data,
> +                                        pgoff_t start, pgoff_t end)
> +{
> +       struct restrictedmem_notifier *notifier;
> +
> +       mutex_lock(&data->lock);
> +       list_for_each_entry(notifier, &data->notifiers, list) {
> +               notifier->ops->error(notifier, start, end);
> +       }
> +       mutex_unlock(&data->lock);
> +}
> +
> +static int restrictedmem_release(struct inode *inode, struct file *file)
> +{
> +       struct restrictedmem_data *data = inode->i_mapping->private_data;
> +
> +       fput(data->memfd);
> +       kfree(data);
> +       return 0;
> +}
> +
> +static long restrictedmem_punch_hole(struct restrictedmem_data *data, int mode,
> +                                    loff_t offset, loff_t len)
> +{
> +       int ret;
> +       pgoff_t start, end;
> +       struct file *memfd = data->memfd;
> +
> +       if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> +               return -EINVAL;
> +
> +       start = offset >> PAGE_SHIFT;
> +       end = (offset + len) >> PAGE_SHIFT;
> +
> +       restrictedmem_invalidate_start(data, start, end);
> +       ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> +       restrictedmem_invalidate_end(data, start, end);
> +
> +       return ret;
> +}
> +
> +static long restrictedmem_fallocate(struct file *file, int mode,
> +                                   loff_t offset, loff_t len)
> +{
> +       struct restrictedmem_data *data = file->f_mapping->private_data;
> +       struct file *memfd = data->memfd;
> +
> +       if (mode & FALLOC_FL_PUNCH_HOLE)
> +               return restrictedmem_punch_hole(data, mode, offset, len);
> +
> +       return memfd->f_op->fallocate(memfd, mode, offset, len);
> +}
> +
> +static const struct file_operations restrictedmem_fops = {
> +       .release = restrictedmem_release,
> +       .fallocate = restrictedmem_fallocate,
> +};
> +
> +static int restrictedmem_getattr(struct user_namespace *mnt_userns,
> +                                const struct path *path, struct kstat *stat,
> +                                u32 request_mask, unsigned int query_flags)
> +{
> +       struct inode *inode = d_inode(path->dentry);
> +       struct restrictedmem_data *data = inode->i_mapping->private_data;
> +       struct file *memfd = data->memfd;
> +
> +       return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> +                                            request_mask, query_flags);
> +}
> +
> +static int restrictedmem_setattr(struct user_namespace *mnt_userns,
> +                                struct dentry *dentry, struct iattr *attr)
> +{
> +       struct inode *inode = d_inode(dentry);
> +       struct restrictedmem_data *data = inode->i_mapping->private_data;
> +       struct file *memfd = data->memfd;
> +       int ret;
> +
> +       if (attr->ia_valid & ATTR_SIZE) {
> +               if (memfd->f_inode->i_size)
> +                       return -EPERM;
> +
> +               if (!PAGE_ALIGNED(attr->ia_size))
> +                       return -EINVAL;
> +       }
> +
> +       ret = memfd->f_inode->i_op->setattr(mnt_userns,
> +                                           file_dentry(memfd), attr);
> +       return ret;
> +}
> +
> +static const struct inode_operations restrictedmem_iops = {
> +       .getattr = restrictedmem_getattr,
> +       .setattr = restrictedmem_setattr,
> +};
> +
> +static int restrictedmem_init_fs_context(struct fs_context *fc)
> +{
> +       if (!init_pseudo(fc, RESTRICTEDMEM_MAGIC))
> +               return -ENOMEM;
> +
> +       fc->s_iflags |= SB_I_NOEXEC;
> +       return 0;
> +}
> +
> +static struct file_system_type restrictedmem_fs = {
> +       .owner          = THIS_MODULE,
> +       .name           = "memfd:restrictedmem",
> +       .init_fs_context = restrictedmem_init_fs_context,
> +       .kill_sb        = kill_anon_super,
> +};
> +
> +static struct vfsmount *restrictedmem_mnt;
> +
> +static __init int restrictedmem_init(void)
> +{
> +       restrictedmem_mnt = kern_mount(&restrictedmem_fs);
> +       if (IS_ERR(restrictedmem_mnt))
> +               return PTR_ERR(restrictedmem_mnt);
> +       return 0;
> +}
> +fs_initcall(restrictedmem_init);
> +
> +static struct file *restrictedmem_file_create(struct file *memfd)
> +{
> +       struct restrictedmem_data *data;
> +       struct address_space *mapping;
> +       struct inode *inode;
> +       struct file *file;
> +
> +       data = kzalloc(sizeof(*data), GFP_KERNEL);
> +       if (!data)
> +               return ERR_PTR(-ENOMEM);
> +
> +       data->memfd = memfd;
> +       mutex_init(&data->lock);
> +       INIT_LIST_HEAD(&data->notifiers);
> +
> +       inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
> +       if (IS_ERR(inode)) {
> +               kfree(data);
> +               return ERR_CAST(inode);
> +       }
> +
> +       inode->i_mode |= S_IFREG;
> +       inode->i_op = &restrictedmem_iops;
> +       inode->i_mapping->private_data = data;
> +
> +       file = alloc_file_pseudo(inode, restrictedmem_mnt,
> +                                "restrictedmem", O_RDWR,
> +                                &restrictedmem_fops);
> +       if (IS_ERR(file)) {
> +               iput(inode);
> +               kfree(data);
> +               return ERR_CAST(file);
> +       }
> +
> +       file->f_flags |= O_LARGEFILE;
> +
> +       /*
> +        * These pages are currently unmovable so don't place them into movable
> +        * pageblocks (e.g. CMA and ZONE_MOVABLE).
> +        */
> +       mapping = memfd->f_mapping;
> +       mapping_set_unevictable(mapping);
> +       mapping_set_gfp_mask(mapping,
> +                            mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> +
> +       return file;
> +}
> +
> +SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> +{
> +       struct file *file, *restricted_file;
> +       int fd, err;
> +
> +       if (flags)
> +               return -EINVAL;
> +
> +       fd = get_unused_fd_flags(0);
> +       if (fd < 0)
> +               return fd;
> +
> +       file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +       if (IS_ERR(file)) {
> +               err = PTR_ERR(file);
> +               goto err_fd;
> +       }
> +       file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
> +       file->f_flags |= O_LARGEFILE;
> +
> +       restricted_file = restrictedmem_file_create(file);
> +       if (IS_ERR(restricted_file)) {
> +               err = PTR_ERR(restricted_file);
> +               fput(file);
> +               goto err_fd;
> +       }
> +
> +       fd_install(fd, restricted_file);
> +       return fd;
> +err_fd:
> +       put_unused_fd(fd);
> +       return err;
> +}
> +
> +void restrictedmem_register_notifier(struct file *file,
> +                                    struct restrictedmem_notifier *notifier)
> +{
> +       struct restrictedmem_data *data = file->f_mapping->private_data;
> +
> +       mutex_lock(&data->lock);
> +       list_add(&notifier->list, &data->notifiers);
> +       mutex_unlock(&data->lock);
> +}
> +EXPORT_SYMBOL_GPL(restrictedmem_register_notifier);
> +
> +void restrictedmem_unregister_notifier(struct file *file,
> +                                      struct restrictedmem_notifier *notifier)
> +{
> +       struct restrictedmem_data *data = file->f_mapping->private_data;
> +
> +       mutex_lock(&data->lock);
> +       list_del(&notifier->list);
> +       mutex_unlock(&data->lock);
> +}
> +EXPORT_SYMBOL_GPL(restrictedmem_unregister_notifier);
> +
> +int restrictedmem_get_page(struct file *file, pgoff_t offset,
> +                          struct page **pagep, int *order)
> +{
> +       struct restrictedmem_data *data = file->f_mapping->private_data;
> +       struct file *memfd = data->memfd;
> +       struct folio *folio;
> +       struct page *page;
> +       int ret;
> +
> +       ret = shmem_get_folio(file_inode(memfd), offset, &folio, SGP_WRITE);
> +       if (ret)
> +               return ret;
> +
> +       page = folio_file_page(folio, offset);
> +       *pagep = page;
> +       if (order)
> +               *order = thp_order(compound_head(page));
> +
> +       SetPageUptodate(page);
> +       unlock_page(page);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(restrictedmem_get_page);
> +
> +void restrictedmem_error_page(struct page *page, struct address_space *mapping)
> +{
> +       struct super_block *sb = restrictedmem_mnt->mnt_sb;
> +       struct inode *inode, *next;
> +
> +       if (!shmem_mapping(mapping))
> +               return;
> +
> +       spin_lock(&sb->s_inode_list_lock);
> +       list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> +               struct restrictedmem_data *data = inode->i_mapping->private_data;
> +               struct file *memfd = data->memfd;
> +
> +               if (memfd->f_mapping == mapping) {
> +                       pgoff_t start, end;
> +
> +                       spin_unlock(&sb->s_inode_list_lock);
> +
> +                       start = page->index;
> +                       end = start + thp_nr_pages(page);
> +                       restrictedmem_notifier_error(data, start, end);
> +                       return;
> +               }
> +       }
> +       spin_unlock(&sb->s_inode_list_lock);
> +}
> --
> 2.25.1
>

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Fuad Tabba]

Hi,

On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> In confidential computing usages, whether a page is private or shared is
> necessary information for KVM to perform operations like page fault
> handling, page zapping etc. There are other potential use cases for
> per-page memory attributes, e.g. to make memory read-only (or no-exec,
> or exec-only, etc.) without having to modify memslots.
>
> Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> userspace to operate on the per-page memory attributes.
>   - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
>     a guest memory range.
>   - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
>     memory attributes.
>
> KVM internally uses xarray to store the per-page memory attributes.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> ---
>  Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
>  arch/x86/kvm/Kconfig           |  1 +
>  include/linux/kvm_host.h       |  3 ++
>  include/uapi/linux/kvm.h       | 17 ++++++++
>  virt/kvm/Kconfig               |  3 ++
>  virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
>  6 files changed, 163 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 5617bc4f899f..bb2f709c0900 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
>  The "pad" and "reserved" fields may be used for future extensions and should be
>  set to 0s by userspace.
>
> +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: u64 memory attributes bitmask(out)
> +:Returns: 0 on success, <0 on error
> +
> +Returns supported memory attributes bitmask. Supported memory attributes will
> +have the corresponding bits set in u64 memory attributes bitmask.
> +
> +The following memory attributes are defined::
> +
> +  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> +
> +4.139 KVM_SET_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: struct kvm_memory_attributes(in/out)
> +:Returns: 0 on success, <0 on error
> +
> +Sets memory attributes for pages in a guest memory range. Parameters are
> +specified via the following structure::
> +
> +  struct kvm_memory_attributes {
> +       __u64 address;
> +       __u64 size;
> +       __u64 attributes;
> +       __u64 flags;
> +  };
> +
> +The user sets the per-page memory attributes to a guest memory range indicated
> +by address/size, and in return KVM adjusts address and size to reflect the
> +actual pages of the memory range have been successfully set to the attributes.
> +If the call returns 0, "address" is updated to the last successful address + 1
> +and "size" is updated to the remaining address size that has not been set
> +successfully. The user should check the return value as well as the size to
> +decide if the operation succeeded for the whole range or not. The user may want
> +to retry the operation with the returned address/size if the previous range was
> +partially successful.
> +
> +Both address and size should be page aligned and the supported attributes can be
> +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> +
> +The "flags" field may be used for future extensions and should be set to 0s.
> +
>  5. The kvm_run structure
>  ========================
>
> @@ -8270,6 +8323,16 @@ structure.
>  When getting the Modified Change Topology Report value, the attr->addr
>  must point to a byte where the value will be stored or retrieved from.
>
> +8.40 KVM_CAP_MEMORY_ATTRIBUTES
> +------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm
> +
> +This capability indicates KVM supports per-page memory attributes and ioctls
> +KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available.
> +
>  9. Known KVM API problems
>  =========================
>
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index fbeaa9ddef59..a8e379a3afee 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -49,6 +49,7 @@ config KVM
>         select SRCU
>         select INTERVAL_TREE
>         select HAVE_KVM_PM_NOTIFIER if PM
> +       select HAVE_KVM_MEMORY_ATTRIBUTES
>         help
>           Support hosting fully virtualized guest machines using hardware
>           virtualization extensions.  You will need a fairly recent
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8f874a964313..a784e2b06625 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -800,6 +800,9 @@ struct kvm {
>
>  #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
>         struct notifier_block pm_notifier;
> +#endif
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +       struct xarray mem_attr_array;
>  #endif
>         char stats_id[KVM_STATS_NAME_SIZE];
>  };
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 64dfe9c07c87..5d0941acb5bb 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1182,6 +1182,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_S390_CPU_TOPOLOGY 222
>  #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
>  #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
> +#define KVM_CAP_MEMORY_ATTRIBUTES 225
>
>  #ifdef KVM_CAP_IRQ_ROUTING
>
> @@ -2238,4 +2239,20 @@ struct kvm_s390_zpci_op {
>  /* flags for kvm_s390_zpci_op->u.reg_aen.flags */
>  #define KVM_S390_ZPCIOP_REGAEN_HOST    (1 << 0)
>
> +/* Available with KVM_CAP_MEMORY_ATTRIBUTES */
> +#define KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES    _IOR(KVMIO,  0xd2, __u64)
> +#define KVM_SET_MEMORY_ATTRIBUTES              _IOWR(KVMIO,  0xd3, struct kvm_memory_attributes)
> +
> +struct kvm_memory_attributes {
> +       __u64 address;
> +       __u64 size;
> +       __u64 attributes;
> +       __u64 flags;
> +};
> +
> +#define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +#define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +#define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +#define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)

nit: how about using the BIT() macro for these?

> +
>  #endif /* __LINUX_KVM_H */
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 800f9470e36b..effdea5dd4f0 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -19,6 +19,9 @@ config HAVE_KVM_IRQ_ROUTING
>  config HAVE_KVM_DIRTY_RING
>         bool
>
> +config HAVE_KVM_MEMORY_ATTRIBUTES
> +       bool
> +
>  # Only strongly ordered architectures can select this, as it doesn't
>  # put any explicit constraint on userspace ordering. They can also
>  # select the _ACQ_REL version.
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1782c4555d94..7f0f5e9f2406 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>         spin_lock_init(&kvm->mn_invalidate_lock);
>         rcuwait_init(&kvm->mn_memslots_update_rcuwait);
>         xa_init(&kvm->vcpu_array);
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +       xa_init(&kvm->mem_attr_array);
> +#endif
>
>         INIT_LIST_HEAD(&kvm->gpc_list);
>         spin_lock_init(&kvm->gpc_lock);
> @@ -1323,6 +1326,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
>                 kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
>                 kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
>         }
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +       xa_destroy(&kvm->mem_attr_array);
> +#endif
>         cleanup_srcu_struct(&kvm->irq_srcu);
>         cleanup_srcu_struct(&kvm->srcu);
>         kvm_arch_free_vm(kvm);
> @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
>  }
>  #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
>
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> +{
> +       return 0;
> +}
> +
> +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> +                                          struct kvm_memory_attributes *attrs)
> +{
> +       gfn_t start, end;
> +       unsigned long i;
> +       void *entry;
> +       u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> +
> +       /* flags is currently not used. */

nit: "is reserved"? I think it makes it a bit clearer what its purpose is.

> +       if (attrs->flags)
> +               return -EINVAL;
> +       if (attrs->attributes & ~supported_attrs)
> +               return -EINVAL;
> +       if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> +               return -EINVAL;
> +       if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> +               return -EINVAL;
> +
> +       start = attrs->address >> PAGE_SHIFT;
> +       end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;

Would using existing helpers be better for getting the frame numbers?
Also, the code checks that the address and size are page aligned, so
the end rounding up seems redundant, and might even be wrong if the
address+size-1 is close to the gfn_t limit (which this code tries to
avoid in an earlier check).

> +       entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> +
> +       mutex_lock(&kvm->lock);
> +       for (i = start; i < end; i++)
> +               if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> +                                   GFP_KERNEL_ACCOUNT)))
> +                       break;
> +       mutex_unlock(&kvm->lock);
> +
> +       attrs->address = i << PAGE_SHIFT;
> +       attrs->size = (end - i) << PAGE_SHIFT;

nit: helpers for these too?

With the end calculation fixed,

Reviewed-by: Fuad Tabba <tabba@google.com>
After adding the necessary configs for arm64 (on qemu/arm64):
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad

> +
> +       return 0;
> +}
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +
>  struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
>  {
>         return __gfn_to_memslot(kvm_memslots(kvm), gfn);
> @@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>  #ifdef CONFIG_HAVE_KVM_MSI
>         case KVM_CAP_SIGNAL_MSI:
>  #endif
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +       case KVM_CAP_MEMORY_ATTRIBUTES:
> +#endif
>  #ifdef CONFIG_HAVE_KVM_IRQFD
>         case KVM_CAP_IRQFD:
>         case KVM_CAP_IRQFD_RESAMPLE:
> @@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp,
>                 break;
>         }
>  #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +       case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: {
> +               u64 attrs = kvm_supported_mem_attributes(kvm);
> +
> +               r = -EFAULT;
> +               if (copy_to_user(argp, &attrs, sizeof(attrs)))
> +                       goto out;
> +               r = 0;
> +               break;
> +       }
> +       case KVM_SET_MEMORY_ATTRIBUTES: {
> +               struct kvm_memory_attributes attrs;
> +
> +               r = -EFAULT;
> +               if (copy_from_user(&attrs, argp, sizeof(attrs)))
> +                       goto out;
> +
> +               r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);
> +
> +               if (!r && copy_to_user(argp, &attrs, sizeof(attrs)))
> +                       r = -EFAULT;
> +               break;
> +       }
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
>         case KVM_CREATE_DEVICE: {
>                 struct kvm_create_device cd;
>
> --
> 2.25.1
>

Re: [PATCH v10 4/9] KVM: Add KVM_EXIT_MEMORY_FAULT exit

[Fuad Tabba]

Hi,

On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> This new KVM exit allows userspace to handle memory-related errors. It
> indicates an error happens in KVM at guest memory range [gpa, gpa+size).
> The flags includes additional information for userspace to handle the
> error. Currently bit 0 is defined as 'private memory' where '1'
> indicates error happens due to private memory access and '0' indicates
> error happens due to shared memory access.
>
> When private memory is enabled, this new exit will be used for KVM to
> exit to userspace for shared <-> private memory conversion in memory
> encryption usage. In such usage, typically there are two kind of memory
> conversions:
>   - explicit conversion: happens when guest explicitly calls into KVM
>     to map a range (as private or shared), KVM then exits to userspace
>     to perform the map/unmap operations.
>   - implicit conversion: happens in KVM page fault handler where KVM
>     exits to userspace for an implicit conversion when the page is in a
>     different state than requested (private or shared).
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> ---
>  Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++++
>  include/uapi/linux/kvm.h       |  8 ++++++++
>  2 files changed, 30 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 99352170c130..d9edb14ce30b 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6634,6 +6634,28 @@ array field represents return values. The userspace should update the return
>  values of SBI call before resuming the VCPU. For more details on RISC-V SBI
>  spec refer, https://github.com/riscv/riscv-sbi-doc.
>
> +::
> +
> +               /* KVM_EXIT_MEMORY_FAULT */
> +               struct {
> +  #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 0)
> +                       __u64 flags;

I see you've removed the padding and increased the flag size.

Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad




> +                       __u64 gpa;
> +                       __u64 size;
> +               } memory;
> +
> +If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has
> +encountered a memory error which is not handled by KVM kernel module and
> +userspace may choose to handle it. The 'flags' field indicates the memory
> +properties of the exit.
> +
> + - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by
> +   private memory access when the bit is set. Otherwise the memory error is
> +   caused by shared memory access when the bit is clear.
> +
> +'gpa' and 'size' indicate the memory range the error occurs at. The userspace
> +may handle the error and return to KVM to retry the previous memory access.
> +
>  ::
>
>      /* KVM_EXIT_NOTIFY */
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 13bff963b8b0..c7e9d375a902 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -300,6 +300,7 @@ struct kvm_xen_exit {
>  #define KVM_EXIT_RISCV_SBI        35
>  #define KVM_EXIT_RISCV_CSR        36
>  #define KVM_EXIT_NOTIFY           37
> +#define KVM_EXIT_MEMORY_FAULT     38
>
>  /* For KVM_EXIT_INTERNAL_ERROR */
>  /* Emulate instruction failed. */
> @@ -541,6 +542,13 @@ struct kvm_run {
>  #define KVM_NOTIFY_CONTEXT_INVALID     (1 << 0)
>                         __u32 flags;
>                 } notify;
> +               /* KVM_EXIT_MEMORY_FAULT */
> +               struct {
> +#define KVM_MEMORY_EXIT_FLAG_PRIVATE   (1ULL << 0)
> +                       __u64 flags;
> +                       __u64 gpa;
> +                       __u64 size;
> +               } memory;
>                 /* Fix the size of the union. */
>                 char padding[256];
>         };
> --
> 2.25.1
>

Re: [PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry

[Fuad Tabba]

Hi,

On Tue, Dec 6, 2022 at 12:01 PM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> On Mon, Dec 05, 2022 at 09:23:49AM +0000, Fuad Tabba wrote:
> > Hi Chao,
> >
> > On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > >
> > > Currently in mmu_notifier invalidate path, hva range is recorded and
> > > then checked against by mmu_notifier_retry_hva() in the page fault
> > > handling path. However, for the to be introduced private memory, a page
> > > fault may not have a hva associated, checking gfn(gpa) makes more sense.
> > >
> > > For existing hva based shared memory, gfn is expected to also work. The
> > > only downside is when aliasing multiple gfns to a single hva, the
> > > current algorithm of checking multiple ranges could result in a much
> > > larger range being rejected. Such aliasing should be uncommon, so the
> > > impact is expected small.
> > >
> > > Suggested-by: Sean Christopherson <seanjc@google.com>
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > ---
> > >  arch/x86/kvm/mmu/mmu.c   |  8 +++++---
> > >  include/linux/kvm_host.h | 33 +++++++++++++++++++++------------
> > >  virt/kvm/kvm_main.c      | 32 +++++++++++++++++++++++---------
> > >  3 files changed, 49 insertions(+), 24 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > index 4736d7849c60..e2c70b5afa3e 100644
> > > --- a/arch/x86/kvm/mmu/mmu.c
> > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > @@ -4259,7 +4259,7 @@ static bool is_page_fault_stale(struct kvm_vcpu *vcpu,
> > >                 return true;
> > >
> > >         return fault->slot &&
> > > -              mmu_invalidate_retry_hva(vcpu->kvm, mmu_seq, fault->hva);
> > > +              mmu_invalidate_retry_gfn(vcpu->kvm, mmu_seq, fault->gfn);
> > >  }
> > >
> > >  static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > > @@ -6098,7 +6098,9 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
> > >
> > >         write_lock(&kvm->mmu_lock);
> > >
> > > -       kvm_mmu_invalidate_begin(kvm, gfn_start, gfn_end);
> > > +       kvm_mmu_invalidate_begin(kvm);
> > > +
> > > +       kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
> > >
> > >         flush = kvm_rmap_zap_gfn_range(kvm, gfn_start, gfn_end);
> > >
> > > @@ -6112,7 +6114,7 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
> > >                 kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
> > >                                                    gfn_end - gfn_start);
> > >
> > > -       kvm_mmu_invalidate_end(kvm, gfn_start, gfn_end);
> > > +       kvm_mmu_invalidate_end(kvm);
> > >
> > >         write_unlock(&kvm->mmu_lock);
> > >  }
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 02347e386ea2..3d69484d2704 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -787,8 +787,8 @@ struct kvm {
> > >         struct mmu_notifier mmu_notifier;
> > >         unsigned long mmu_invalidate_seq;
> > >         long mmu_invalidate_in_progress;
> > > -       unsigned long mmu_invalidate_range_start;
> > > -       unsigned long mmu_invalidate_range_end;
> > > +       gfn_t mmu_invalidate_range_start;
> > > +       gfn_t mmu_invalidate_range_end;
> > >  #endif
> > >         struct list_head devices;
> > >         u64 manual_dirty_log_protect;
> > > @@ -1389,10 +1389,9 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
> > >  void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> > >  #endif
> > >
> > > -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> > > -                             unsigned long end);
> > > -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> > > -                           unsigned long end);
> > > +void kvm_mmu_invalidate_begin(struct kvm *kvm);
> > > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end);
> > > +void kvm_mmu_invalidate_end(struct kvm *kvm);
> > >
> > >  long kvm_arch_dev_ioctl(struct file *filp,
> > >                         unsigned int ioctl, unsigned long arg);
> > > @@ -1963,9 +1962,9 @@ static inline int mmu_invalidate_retry(struct kvm *kvm, unsigned long mmu_seq)
> > >         return 0;
> > >  }
> > >
> > > -static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
> > > +static inline int mmu_invalidate_retry_gfn(struct kvm *kvm,
> > >                                            unsigned long mmu_seq,
> > > -                                          unsigned long hva)
> > > +                                          gfn_t gfn)
> > >  {
> > >         lockdep_assert_held(&kvm->mmu_lock);
> > >         /*
> > > @@ -1974,10 +1973,20 @@ static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
> > >          * that might be being invalidated. Note that it may include some false
> >
> > nit: "might be" (or) "is being"
> >
> > >          * positives, due to shortcuts when handing concurrent invalidations.
> >
> > nit: handling
>
> Both are existing code, but I can fix it either.

That was just a nit, please feel free to ignore it, especially if it
might cause headaches in the future with merges.
>
> >
> > >          */
> > > -       if (unlikely(kvm->mmu_invalidate_in_progress) &&
> > > -           hva >= kvm->mmu_invalidate_range_start &&
> > > -           hva < kvm->mmu_invalidate_range_end)
> > > -               return 1;
> > > +       if (unlikely(kvm->mmu_invalidate_in_progress)) {
> > > +               /*
> > > +                * Dropping mmu_lock after bumping mmu_invalidate_in_progress
> > > +                * but before updating the range is a KVM bug.
> > > +                */
> > > +               if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
> > > +                                kvm->mmu_invalidate_range_end == INVALID_GPA))
> >
> > INVALID_GPA is an x86-specific define in
> > arch/x86/include/asm/kvm_host.h, so this doesn't build on other
> > architectures. The obvious fix is to move it to
> > include/linux/kvm_host.h.
>
> Hmm, INVALID_GPA is defined as ZERO for x86, not 100% confident this is
> correct choice for other architectures, but after search it has not been
> used for other architectures, so should be safe to make it common.

With this fixed,

Reviewed-by: Fuad Tabba <tabba@google.com>
And the necessary work to port to arm64 (on qemu/arm64):
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad


>
> Thanks,
> Chao
> >
> > Cheers,
> > /fuad
> >
> > > +                       return 1;
> > > +
> > > +               if (gfn >= kvm->mmu_invalidate_range_start &&
> > > +                   gfn < kvm->mmu_invalidate_range_end)
> > > +                       return 1;
> > > +       }
> > > +
> > >         if (kvm->mmu_invalidate_seq != mmu_seq)
> > >                 return 1;
> > >         return 0;
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index b882eb2c76a2..ad55dfbc75d7 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -540,9 +540,7 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,
> > >
> > >  typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
> > >
> > > -typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
> > > -                            unsigned long end);
> > > -
> > > +typedef void (*on_lock_fn_t)(struct kvm *kvm);
> > >  typedef void (*on_unlock_fn_t)(struct kvm *kvm);
> > >
> > >  struct kvm_hva_range {
> > > @@ -628,7 +626,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
> > >                                 locked = true;
> > >                                 KVM_MMU_LOCK(kvm);
> > >                                 if (!IS_KVM_NULL_FN(range->on_lock))
> > > -                                       range->on_lock(kvm, range->start, range->end);
> > > +                                       range->on_lock(kvm);
> > > +
> > >                                 if (IS_KVM_NULL_FN(range->handler))
> > >                                         break;
> > >                         }
> > > @@ -715,8 +714,7 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> > >         kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> > >  }
> > >
> > > -void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> > > -                             unsigned long end)
> > > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > >  {
> > >         /*
> > >          * The count increase must become visible at unlock time as no
> > > @@ -724,6 +722,17 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> > >          * count is also read inside the mmu_lock critical section.
> > >          */
> > >         kvm->mmu_invalidate_in_progress++;
> > > +
> > > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > +               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > +               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > +       }
> > > +}
> > > +
> > > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > > +{
> > > +       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > +
> > >         if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > >                 kvm->mmu_invalidate_range_start = start;
> > >                 kvm->mmu_invalidate_range_end = end;
> > > @@ -744,6 +753,12 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
> > >         }
> > >  }
> > >
> > > +static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> > > +{
> > > +       kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > > +       return kvm_unmap_gfn_range(kvm, range);
> > > +}
> > > +
> > >  static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> > >                                         const struct mmu_notifier_range *range)
> > >  {
> > > @@ -752,7 +767,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> > >                 .start          = range->start,
> > >                 .end            = range->end,
> > >                 .pte            = __pte(0),
> > > -               .handler        = kvm_unmap_gfn_range,
> > > +               .handler        = kvm_mmu_unmap_gfn_range,
> > >                 .on_lock        = kvm_mmu_invalidate_begin,
> > >                 .on_unlock      = kvm_arch_guest_memory_reclaimed,
> > >                 .flush_on_ret   = true,
> > > @@ -791,8 +806,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> > >         return 0;
> > >  }
> > >
> > > -void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
> > > -                           unsigned long end)
> > > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> > >  {
> > >         /*
> > >          * This sequence increase will notify the kvm page fault that
> > > --
> > > 2.25.1
> > >

Re: [PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry

[Isaku Yamahata]

On Tue, Dec 06, 2022 at 07:56:23PM +0800,
Chao Peng <chao.p.peng@linux.intel.com> wrote:

> > > -       if (unlikely(kvm->mmu_invalidate_in_progress) &&
> > > -           hva >= kvm->mmu_invalidate_range_start &&
> > > -           hva < kvm->mmu_invalidate_range_end)
> > > -               return 1;
> > > +       if (unlikely(kvm->mmu_invalidate_in_progress)) {
> > > +               /*
> > > +                * Dropping mmu_lock after bumping mmu_invalidate_in_progress
> > > +                * but before updating the range is a KVM bug.
> > > +                */
> > > +               if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
> > > +                                kvm->mmu_invalidate_range_end == INVALID_GPA))
> > 
> > INVALID_GPA is an x86-specific define in
> > arch/x86/include/asm/kvm_host.h, so this doesn't build on other
> > architectures. The obvious fix is to move it to
> > include/linux/kvm_host.h.
> 
> Hmm, INVALID_GPA is defined as ZERO for x86, not 100% confident this is
> correct choice for other architectures, but after search it has not been
> used for other architectures, so should be safe to make it common.

INVALID_GPA is defined as all bit 1.  Please notice "~" (tilde).

#define INVALID_GPA (~(gpa_t)0)
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Isaku Yamahata]

On Tue, Dec 06, 2022 at 08:02:24PM +0800,
Chao Peng <chao.p.peng@linux.intel.com> wrote:

> On Mon, Dec 05, 2022 at 02:49:59PM -0800, Isaku Yamahata wrote:
> > On Fri, Dec 02, 2022 at 02:13:45PM +0800,
> > Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > 
> > > A large page with mixed private/shared subpages can't be mapped as large
> > > page since its sub private/shared pages are from different memory
> > > backends and may also treated by architecture differently. When
> > > private/shared memory are mixed in a large page, the current lpage_info
> > > is not sufficient to decide whether the page can be mapped as large page
> > > or not and additional private/shared mixed information is needed.
> > > 
> > > Tracking this 'mixed' information with the current 'count' like
> > > disallow_lpage is a bit challenge so reserve a bit in 'disallow_lpage'
> > > to indicate a large page has mixed private/share subpages and update
> > > this 'mixed' bit whenever the memory attribute is changed between
> > > private and shared.
> > > 
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > ---
> > >  arch/x86/include/asm/kvm_host.h |   8 ++
> > >  arch/x86/kvm/mmu/mmu.c          | 134 +++++++++++++++++++++++++++++++-
> > >  arch/x86/kvm/x86.c              |   2 +
> > >  include/linux/kvm_host.h        |  19 +++++
> > >  virt/kvm/kvm_main.c             |   9 ++-
> > >  5 files changed, 169 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > > index 283cbb83d6ae..7772ab37ac89 100644
> > > --- a/arch/x86/include/asm/kvm_host.h
> > > +++ b/arch/x86/include/asm/kvm_host.h
> > > @@ -38,6 +38,7 @@
> > >  #include <asm/hyperv-tlfs.h>
> > >  
> > >  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
> > > +#define __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
> > >  
> > >  #define KVM_MAX_VCPUS 1024
> > >  
> > > @@ -1011,6 +1012,13 @@ struct kvm_vcpu_arch {
> > >  #endif
> > >  };
> > >  
> > > +/*
> > > + * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
> > > + * level. The remaining bits are used as a reference count.
> > > + */
> > > +#define KVM_LPAGE_PRIVATE_SHARED_MIXED		(1U << 31)
> > > +#define KVM_LPAGE_COUNT_MAX			((1U << 31) - 1)
> > > +
> > >  struct kvm_lpage_info {
> > >  	int disallow_lpage;
> > >  };
> > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > index e2c70b5afa3e..2190fd8c95c0 100644
> > > --- a/arch/x86/kvm/mmu/mmu.c
> > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > @@ -763,11 +763,16 @@ static void update_gfn_disallow_lpage_count(const struct kvm_memory_slot *slot,
> > >  {
> > >  	struct kvm_lpage_info *linfo;
> > >  	int i;
> > > +	int disallow_count;
> > >  
> > >  	for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
> > >  		linfo = lpage_info_slot(gfn, slot, i);
> > > +
> > > +		disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
> > > +		WARN_ON(disallow_count + count < 0 ||
> > > +			disallow_count > KVM_LPAGE_COUNT_MAX - count);
> > > +
> > >  		linfo->disallow_lpage += count;
> > > -		WARN_ON(linfo->disallow_lpage < 0);
> > >  	}
> > >  }
> > >  
> > > @@ -6986,3 +6991,130 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
> > >  	if (kvm->arch.nx_huge_page_recovery_thread)
> > >  		kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
> > >  }
> > > +
> > > +static bool linfo_is_mixed(struct kvm_lpage_info *linfo)
> > > +{
> > > +	return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > > +}
> > > +
> > > +static void linfo_set_mixed(gfn_t gfn, struct kvm_memory_slot *slot,
> > > +			    int level, bool mixed)
> > > +{
> > > +	struct kvm_lpage_info *linfo = lpage_info_slot(gfn, slot, level);
> > > +
> > > +	if (mixed)
> > > +		linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > > +	else
> > > +		linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > > +}
> > > +
> > > +static bool is_expected_attr_entry(void *entry, unsigned long expected_attrs)
> > > +{
> > > +	bool expect_private = expected_attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > > +
> > > +	if (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) {
> > > +		if (!expect_private)
> > > +			return false;
> > > +	} else if (expect_private)
> > > +		return false;
> > > +
> > > +	return true;
> > > +}
> > > +
> > > +static bool mem_attrs_mixed_2m(struct kvm *kvm, unsigned long attrs,
> > > +			       gfn_t start, gfn_t end)
> > > +{
> > > +	XA_STATE(xas, &kvm->mem_attr_array, start);
> > > +	gfn_t gfn = start;
> > > +	void *entry;
> > > +	bool mixed = false;
> > > +
> > > +	rcu_read_lock();
> > > +	entry = xas_load(&xas);
> > > +	while (gfn < end) {
> > > +		if (xas_retry(&xas, entry))
> > > +			continue;
> > > +
> > > +		KVM_BUG_ON(gfn != xas.xa_index, kvm);
> > > +
> > > +		if (!is_expected_attr_entry(entry, attrs)) {
> > > +			mixed = true;
> > > +			break;
> > > +		}
> > > +
> > > +		entry = xas_next(&xas);
> > > +		gfn++;
> > > +	}
> > > +
> > > +	rcu_read_unlock();
> > > +	return mixed;
> > > +}
> > > +
> > > +static bool mem_attrs_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
> > > +			    int level, unsigned long attrs,
> > > +			    gfn_t start, gfn_t end)
> > > +{
> > > +	unsigned long gfn;
> > > +
> > > +	if (level == PG_LEVEL_2M)
> > > +		return mem_attrs_mixed_2m(kvm, attrs, start, end);
> > > +
> > > +	for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1))
> > > +		if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
> > > +		    !is_expected_attr_entry(xa_load(&kvm->mem_attr_array, gfn),
> > > +					    attrs))
> > > +			return true;
> > > +	return false;
> > > +}
> > > +
> > > +static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
> > > +						  struct kvm_memory_slot *slot,
> > > +						  unsigned long attrs,
> > > +						  gfn_t start, gfn_t end)
> > > +{
> > > +	unsigned long pages, mask;
> > > +	gfn_t gfn, gfn_end, first, last;
> > > +	int level;
> > > +	bool mixed;
> > > +
> > > +	/*
> > > +	 * The sequence matters here: we set the higher level basing on the
> > > +	 * lower level's scanning result.
> > > +	 */
> > > +	for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> > > +		pages = KVM_PAGES_PER_HPAGE(level);
> > > +		mask = ~(pages - 1);
> > > +		first = start & mask;
> > > +		last = (end - 1) & mask;
> > > +
> > > +		/*
> > > +		 * We only need to scan the head and tail page, for middle pages
> > > +		 * we know they will not be mixed.
> > > +		 */
> > > +		gfn = max(first, slot->base_gfn);
> > > +		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
> > > +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> > > +		linfo_set_mixed(gfn, slot, level, mixed);
> > > +
> > > +		if (first == last)
> > > +			return;
> > 
> > 
> > continue.
> 
> Ya!
> 
> > 
> > > +
> > > +		for (gfn = first + pages; gfn < last; gfn += pages)
> > > +			linfo_set_mixed(gfn, slot, level, false);
> > > +
> > > +		gfn = last;
> > > +		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
> > 
> > if (gfn == gfn_end) continue.
> 
> Do you see a case where gfn can equal to gfn_end? Though it does not
> hurt to add a check.

If last == base_gfn + npages, gfn == gfn_end can occur.


> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index 9a07380f8d3c..5aefcff614d2 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
> > >  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
> > >  			linfo[lpages - 1].disallow_lpage = 1;
> > >  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> > > +		if (kvm_slot_can_be_private(slot))
> > > +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
> > 
> > Is there any alignment restriction? If no, It should be +=.
> > In practice, alignment will hold though.
> 
> All we need here is checking whether both userspace_addr and
> restricted_offset are aligned to HPAGE_SIZE or not. '+=' actually can
> yield wrong value in cases when userspace_addr + restricted_offset is
> aligned to HPAGE_SIZE but individually they may not align to HPAGE_SIZE.

Ah, got it. The blow comment explains it.

> Thanks,
> Chao
> > 
> > Thanks,
> > 
> > >  		/*
> > >  		 * If the gfn and userspace address are not aligned wrt each
> > >  		 * other, disable large page support for this slot.
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Yuan Yao]

On Fri, Dec 02, 2022 at 02:13:44PM +0800, Chao Peng wrote:
> Unmap the existing guest mappings when memory attribute is changed
> between shared and private. This is needed because shared pages and
> private pages are from different backends, unmapping existing ones
> gives a chance for page fault handler to re-populate the mappings
> according to the new attribute.
>
> Only architecture has private memory support needs this and the
> supported architecture is expected to rewrite the weak
> kvm_arch_has_private_mem().
>
> Also, during memory attribute changing and the unmapping time frame,
> page fault handler may happen in the same memory range and can cause
> incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> page fault handler retry during this time frame.
>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  include/linux/kvm_host.h |   7 +-
>  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
>  2 files changed, 116 insertions(+), 59 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3d69484d2704..3331c0c92838 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
>  #endif
>
> -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
>  struct kvm_gfn_range {
>  	struct kvm_memory_slot *slot;
>  	gfn_t start;
> @@ -264,6 +263,8 @@ struct kvm_gfn_range {
>  	bool may_block;
>  };
>  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> +
> +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
>  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> @@ -785,11 +786,12 @@ struct kvm {
>
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  	struct mmu_notifier mmu_notifier;
> +#endif
>  	unsigned long mmu_invalidate_seq;
>  	long mmu_invalidate_in_progress;
>  	gfn_t mmu_invalidate_range_start;
>  	gfn_t mmu_invalidate_range_end;
> -#endif
> +
>  	struct list_head devices;
>  	u64 manual_dirty_log_protect;
>  	struct dentry *debugfs_dentry;
> @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
>  int kvm_arch_post_init_vm(struct kvm *kvm);
>  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
>  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> +bool kvm_arch_has_private_mem(struct kvm *kvm);
>
>  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
>  /*
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index ad55dfbc75d7..4e1e1e113bf0 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
>  }
>  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
>
> +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> +{
> +	/*
> +	 * The count increase must become visible at unlock time as no
> +	 * spte can be established without taking the mmu_lock and
> +	 * count is also read inside the mmu_lock critical section.
> +	 */
> +	kvm->mmu_invalidate_in_progress++;
> +
> +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +		kvm->mmu_invalidate_range_start = INVALID_GPA;
> +		kvm->mmu_invalidate_range_end = INVALID_GPA;
> +	}
> +}
> +
> +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> +
> +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +		kvm->mmu_invalidate_range_start = start;
> +		kvm->mmu_invalidate_range_end = end;
> +	} else {
> +		/*
> +		 * Fully tracking multiple concurrent ranges has diminishing
> +		 * returns. Keep things simple and just find the minimal range
> +		 * which includes the current and new ranges. As there won't be
> +		 * enough information to subtract a range after its invalidate
> +		 * completes, any ranges invalidated concurrently will
> +		 * accumulate and persist until all outstanding invalidates
> +		 * complete.
> +		 */
> +		kvm->mmu_invalidate_range_start =
> +			min(kvm->mmu_invalidate_range_start, start);
> +		kvm->mmu_invalidate_range_end =
> +			max(kvm->mmu_invalidate_range_end, end);
> +	}
> +}
> +
> +void kvm_mmu_invalidate_end(struct kvm *kvm)
> +{
> +	/*
> +	 * This sequence increase will notify the kvm page fault that
> +	 * the page that is going to be mapped in the spte could have
> +	 * been freed.
> +	 */
> +	kvm->mmu_invalidate_seq++;
> +	smp_wmb();
> +	/*
> +	 * The above sequence increase must be visible before the
> +	 * below count decrease, which is ensured by the smp_wmb above
> +	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> +	 */
> +	kvm->mmu_invalidate_in_progress--;
> +}
> +
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
>  {
> @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
>  	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
>  }
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> -{
> -	/*
> -	 * The count increase must become visible at unlock time as no
> -	 * spte can be established without taking the mmu_lock and
> -	 * count is also read inside the mmu_lock critical section.
> -	 */
> -	kvm->mmu_invalidate_in_progress++;
> -
> -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> -		kvm->mmu_invalidate_range_start = INVALID_GPA;
> -		kvm->mmu_invalidate_range_end = INVALID_GPA;
> -	}
> -}
> -
> -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> -	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> -
> -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> -		kvm->mmu_invalidate_range_start = start;
> -		kvm->mmu_invalidate_range_end = end;
> -	} else {
> -		/*
> -		 * Fully tracking multiple concurrent ranges has diminishing
> -		 * returns. Keep things simple and just find the minimal range
> -		 * which includes the current and new ranges. As there won't be
> -		 * enough information to subtract a range after its invalidate
> -		 * completes, any ranges invalidated concurrently will
> -		 * accumulate and persist until all outstanding invalidates
> -		 * complete.
> -		 */
> -		kvm->mmu_invalidate_range_start =
> -			min(kvm->mmu_invalidate_range_start, start);
> -		kvm->mmu_invalidate_range_end =
> -			max(kvm->mmu_invalidate_range_end, end);
> -	}
> -}
> -
>  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>  {
>  	kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>  	return 0;
>  }
>
> -void kvm_mmu_invalidate_end(struct kvm *kvm)
> -{
> -	/*
> -	 * This sequence increase will notify the kvm page fault that
> -	 * the page that is going to be mapped in the spte could have
> -	 * been freed.
> -	 */
> -	kvm->mmu_invalidate_seq++;
> -	smp_wmb();
> -	/*
> -	 * The above sequence increase must be visible before the
> -	 * below count decrease, which is ensured by the smp_wmb above
> -	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> -	 */
> -	kvm->mmu_invalidate_in_progress--;
> -}
> -
>  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
>  					const struct mmu_notifier_range *range)
>  {
> @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
>  	return 0;
>  }
>
> +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> +{
> +	return false;
> +}
> +
>  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>  {
>  	struct kvm *kvm = kvm_arch_alloc_vm();
> @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>  	return 0;
>  }
>
> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	struct kvm_gfn_range gfn_range;
> +	struct kvm_memory_slot *slot;
> +	struct kvm_memslots *slots;
> +	struct kvm_memslot_iter iter;
> +	int i;
> +	int r = 0;
> +
> +	gfn_range.pte = __pte(0);
> +	gfn_range.may_block = true;
> +
> +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +		slots = __kvm_memslots(kvm, i);
> +
> +		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> +			slot = iter.slot;
> +			gfn_range.start = max(start, slot->base_gfn);
> +			gfn_range.end = min(end, slot->base_gfn + slot->npages);
> +			if (gfn_range.start >= gfn_range.end)
> +				continue;
> +			gfn_range.slot = slot;
> +
> +			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> +		}
> +	}
> +
> +	if (r)
> +		kvm_flush_remote_tlbs(kvm);
> +}
> +
>  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  					   struct kvm_memory_attributes *attrs)
>  {
>  	gfn_t start, end;
>  	unsigned long i;
>  	void *entry;
> +	int idx;
>  	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
>
> -	/* flags is currently not used. */
> +	/* 'flags' is currently not used. */
>  	if (attrs->flags)
>  		return -EINVAL;
>  	if (attrs->attributes & ~supported_attrs)
> @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>
>  	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
>
> +	if (kvm_arch_has_private_mem(kvm)) {
> +		KVM_MMU_LOCK(kvm);
> +		kvm_mmu_invalidate_begin(kvm);
> +		kvm_mmu_invalidate_range_add(kvm, start, end);

Nit: this works for KVM_MEMORY_ATTRIBUTE_PRIVATE, but
the invalidation should be necessary yet for attribute change of:

KVM_MEMORY_ATTRIBUTE_READ
KVM_MEMORY_ATTRIBUTE_WRITE
KVM_MEMORY_ATTRIBUTE_EXECUTE

> +		KVM_MMU_UNLOCK(kvm);
> +	}
> +
>  	mutex_lock(&kvm->lock);
>  	for (i = start; i < end; i++)
>  		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  			break;
>  	mutex_unlock(&kvm->lock);
>
> +	if (kvm_arch_has_private_mem(kvm)) {
> +		idx = srcu_read_lock(&kvm->srcu);
> +		KVM_MMU_LOCK(kvm);
> +		if (i > start)
> +			kvm_unmap_mem_range(kvm, start, i);
> +		kvm_mmu_invalidate_end(kvm);

Ditto.

> +		KVM_MMU_UNLOCK(kvm);
> +		srcu_read_unlock(&kvm->srcu, idx);
> +	}
> +
>  	attrs->address = i << PAGE_SHIFT;
>  	attrs->size = (end - i) << PAGE_SHIFT;
>
> --
> 2.25.1
>
>

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Tue, Dec 06, 2022 at 02:57:04PM +0000, Fuad Tabba wrote:
> Hi,
> 
> On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> >
> > Introduce 'memfd_restricted' system call with the ability to create
> > memory areas that are restricted from userspace access through ordinary
> > MMU operations (e.g. read/write/mmap). The memory content is expected to
> > be used through the new in-kernel interface by a third kernel module.
> >
> > memfd_restricted() is useful for scenarios where a file descriptor(fd)
> > can be used as an interface into mm but want to restrict userspace's
> > ability on the fd. Initially it is designed to provide protections for
> > KVM encrypted guest memory.
> >
> > Normally KVM uses memfd memory via mmapping the memfd into KVM userspace
> > (e.g. QEMU) and then using the mmaped virtual address to setup the
> > mapping in the KVM secondary page table (e.g. EPT). With confidential
> > computing technologies like Intel TDX, the memfd memory may be encrypted
> > with special key for special software domain (e.g. KVM guest) and is not
> > expected to be directly accessed by userspace. Precisely, userspace
> > access to such encrypted memory may lead to host crash so should be
> > prevented.
> >
> > memfd_restricted() provides semantics required for KVM guest encrypted
> > memory support that a fd created with memfd_restricted() is going to be
> > used as the source of guest memory in confidential computing environment
> > and KVM can directly interact with core-mm without the need to expose
> > the memoy content into KVM userspace.
> 
> nit: memory

Ya!

> 
> >
> > KVM userspace is still in charge of the lifecycle of the fd. It should
> > pass the created fd to KVM. KVM uses the new restrictedmem_get_page() to
> > obtain the physical memory page and then uses it to populate the KVM
> > secondary page table entries.
> >
> > The userspace restricted memfd can be fallocate-ed or hole-punched
> > from userspace. When hole-punched, KVM can get notified through
> > invalidate_start/invalidate_end() callbacks, KVM then gets chance to
> > remove any mapped entries of the range in the secondary page tables.
> >
> > Machine check can happen for memory pages in the restricted memfd,
> > instead of routing this directly to userspace, we call the error()
> > callback that KVM registered. KVM then gets chance to handle it
> > correctly.
> >
> > memfd_restricted() itself is implemented as a shim layer on top of real
> > memory file systems (currently tmpfs). Pages in restrictedmem are marked
> > as unmovable and unevictable, this is required for current confidential
> > usage. But in future this might be changed.
> >
> > By default memfd_restricted() prevents userspace read, write and mmap.
> > By defining new bit in the 'flags', it can be extended to support other
> > restricted semantics in the future.
> >
> > The system call is currently wired up for x86 arch.
> 
> Reviewed-by: Fuad Tabba <tabba@google.com>
> After wiring the system call for arm64 (on qemu/arm64):
> Tested-by: Fuad Tabba <tabba@google.com>

Thanks.
Chao
> 
> Cheers,
> /fuad
> 
> 
> 
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  arch/x86/entry/syscalls/syscall_32.tbl |   1 +
> >  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
> >  include/linux/restrictedmem.h          |  71 ++++++
> >  include/linux/syscalls.h               |   1 +
> >  include/uapi/asm-generic/unistd.h      |   5 +-
> >  include/uapi/linux/magic.h             |   1 +
> >  kernel/sys_ni.c                        |   3 +
> >  mm/Kconfig                             |   4 +
> >  mm/Makefile                            |   1 +
> >  mm/memory-failure.c                    |   3 +
> >  mm/restrictedmem.c                     | 318 +++++++++++++++++++++++++
> >  11 files changed, 408 insertions(+), 1 deletion(-)
> >  create mode 100644 include/linux/restrictedmem.h
> >  create mode 100644 mm/restrictedmem.c
> >
> > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> > index 320480a8db4f..dc70ba90247e 100644
> > --- a/arch/x86/entry/syscalls/syscall_32.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> > @@ -455,3 +455,4 @@
> >  448    i386    process_mrelease        sys_process_mrelease
> >  449    i386    futex_waitv             sys_futex_waitv
> >  450    i386    set_mempolicy_home_node         sys_set_mempolicy_home_node
> > +451    i386    memfd_restricted        sys_memfd_restricted
> > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> > index c84d12608cd2..06516abc8318 100644
> > --- a/arch/x86/entry/syscalls/syscall_64.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> > @@ -372,6 +372,7 @@
> >  448    common  process_mrelease        sys_process_mrelease
> >  449    common  futex_waitv             sys_futex_waitv
> >  450    common  set_mempolicy_home_node sys_set_mempolicy_home_node
> > +451    common  memfd_restricted        sys_memfd_restricted
> >
> >  #
> >  # Due to a historical design error, certain syscalls are numbered differently
> > diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
> > new file mode 100644
> > index 000000000000..c2700c5daa43
> > --- /dev/null
> > +++ b/include/linux/restrictedmem.h
> > @@ -0,0 +1,71 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +#ifndef _LINUX_RESTRICTEDMEM_H
> > +
> > +#include <linux/file.h>
> > +#include <linux/magic.h>
> > +#include <linux/pfn_t.h>
> > +
> > +struct restrictedmem_notifier;
> > +
> > +struct restrictedmem_notifier_ops {
> > +       void (*invalidate_start)(struct restrictedmem_notifier *notifier,
> > +                                pgoff_t start, pgoff_t end);
> > +       void (*invalidate_end)(struct restrictedmem_notifier *notifier,
> > +                              pgoff_t start, pgoff_t end);
> > +       void (*error)(struct restrictedmem_notifier *notifier,
> > +                              pgoff_t start, pgoff_t end);
> > +};
> > +
> > +struct restrictedmem_notifier {
> > +       struct list_head list;
> > +       const struct restrictedmem_notifier_ops *ops;
> > +};
> > +
> > +#ifdef CONFIG_RESTRICTEDMEM
> > +
> > +void restrictedmem_register_notifier(struct file *file,
> > +                                    struct restrictedmem_notifier *notifier);
> > +void restrictedmem_unregister_notifier(struct file *file,
> > +                                      struct restrictedmem_notifier *notifier);
> > +
> > +int restrictedmem_get_page(struct file *file, pgoff_t offset,
> > +                          struct page **pagep, int *order);
> > +
> > +static inline bool file_is_restrictedmem(struct file *file)
> > +{
> > +       return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC;
> > +}
> > +
> > +void restrictedmem_error_page(struct page *page, struct address_space *mapping);
> > +
> > +#else
> > +
> > +static inline void restrictedmem_register_notifier(struct file *file,
> > +                                    struct restrictedmem_notifier *notifier)
> > +{
> > +}
> > +
> > +static inline void restrictedmem_unregister_notifier(struct file *file,
> > +                                      struct restrictedmem_notifier *notifier)
> > +{
> > +}
> > +
> > +static inline int restrictedmem_get_page(struct file *file, pgoff_t offset,
> > +                                        struct page **pagep, int *order)
> > +{
> > +       return -1;
> > +}
> > +
> > +static inline bool file_is_restrictedmem(struct file *file)
> > +{
> > +       return false;
> > +}
> > +
> > +static inline void restrictedmem_error_page(struct page *page,
> > +                                           struct address_space *mapping)
> > +{
> > +}
> > +
> > +#endif /* CONFIG_RESTRICTEDMEM */
> > +
> > +#endif /* _LINUX_RESTRICTEDMEM_H */
> > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > index a34b0f9a9972..f9e9e0c820c5 100644
> > --- a/include/linux/syscalls.h
> > +++ b/include/linux/syscalls.h
> > @@ -1056,6 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
> >  asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
> >                                             unsigned long home_node,
> >                                             unsigned long flags);
> > +asmlinkage long sys_memfd_restricted(unsigned int flags);
> >
> >  /*
> >   * Architecture-specific system calls
> > diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> > index 45fa180cc56a..e93cd35e46d0 100644
> > --- a/include/uapi/asm-generic/unistd.h
> > +++ b/include/uapi/asm-generic/unistd.h
> > @@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
> >  #define __NR_set_mempolicy_home_node 450
> >  __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
> >
> > +#define __NR_memfd_restricted 451
> > +__SYSCALL(__NR_memfd_restricted, sys_memfd_restricted)
> > +
> >  #undef __NR_syscalls
> > -#define __NR_syscalls 451
> > +#define __NR_syscalls 452
> >
> >  /*
> >   * 32 bit systems traditionally used different
> > diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> > index 6325d1d0e90f..8aa38324b90a 100644
> > --- a/include/uapi/linux/magic.h
> > +++ b/include/uapi/linux/magic.h
> > @@ -101,5 +101,6 @@
> >  #define DMA_BUF_MAGIC          0x444d4142      /* "DMAB" */
> >  #define DEVMEM_MAGIC           0x454d444d      /* "DMEM" */
> >  #define SECRETMEM_MAGIC                0x5345434d      /* "SECM" */
> > +#define RESTRICTEDMEM_MAGIC    0x5245534d      /* "RESM" */
> >
> >  #endif /* __LINUX_MAGIC_H__ */
> > diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> > index 860b2dcf3ac4..7c4a32cbd2e7 100644
> > --- a/kernel/sys_ni.c
> > +++ b/kernel/sys_ni.c
> > @@ -360,6 +360,9 @@ COND_SYSCALL(pkey_free);
> >  /* memfd_secret */
> >  COND_SYSCALL(memfd_secret);
> >
> > +/* memfd_restricted */
> > +COND_SYSCALL(memfd_restricted);
> > +
> >  /*
> >   * Architecture specific weak syscall entries.
> >   */
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > index 57e1d8c5b505..06b0e1d6b8c1 100644
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -1076,6 +1076,10 @@ config IO_MAPPING
> >  config SECRETMEM
> >         def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
> >
> > +config RESTRICTEDMEM
> > +       bool
> > +       depends on TMPFS
> > +
> >  config ANON_VMA_NAME
> >         bool "Anonymous VMA name support"
> >         depends on PROC_FS && ADVISE_SYSCALLS && MMU
> > diff --git a/mm/Makefile b/mm/Makefile
> > index 8e105e5b3e29..bcbb0edf9ba1 100644
> > --- a/mm/Makefile
> > +++ b/mm/Makefile
> > @@ -121,6 +121,7 @@ obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
> >  obj-$(CONFIG_PAGE_TABLE_CHECK) += page_table_check.o
> >  obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
> >  obj-$(CONFIG_SECRETMEM) += secretmem.o
> > +obj-$(CONFIG_RESTRICTEDMEM) += restrictedmem.o
> >  obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o
> >  obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
> >  obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index 145bb561ddb3..f91b444e471e 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -62,6 +62,7 @@
> >  #include <linux/page-isolation.h>
> >  #include <linux/pagewalk.h>
> >  #include <linux/shmem_fs.h>
> > +#include <linux/restrictedmem.h>
> >  #include "swap.h"
> >  #include "internal.h"
> >  #include "ras/ras_event.h"
> > @@ -940,6 +941,8 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
> >                 goto out;
> >         }
> >
> > +       restrictedmem_error_page(p, mapping);
> > +
> >         /*
> >          * The shmem page is kept in page cache instead of truncating
> >          * so is expected to have an extra refcount after error-handling.
> > diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> > new file mode 100644
> > index 000000000000..56953c204e5c
> > --- /dev/null
> > +++ b/mm/restrictedmem.c
> > @@ -0,0 +1,318 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "linux/sbitmap.h"
> > +#include <linux/pagemap.h>
> > +#include <linux/pseudo_fs.h>
> > +#include <linux/shmem_fs.h>
> > +#include <linux/syscalls.h>
> > +#include <uapi/linux/falloc.h>
> > +#include <uapi/linux/magic.h>
> > +#include <linux/restrictedmem.h>
> > +
> > +struct restrictedmem_data {
> > +       struct mutex lock;
> > +       struct file *memfd;
> > +       struct list_head notifiers;
> > +};
> > +
> > +static void restrictedmem_invalidate_start(struct restrictedmem_data *data,
> > +                                          pgoff_t start, pgoff_t end)
> > +{
> > +       struct restrictedmem_notifier *notifier;
> > +
> > +       mutex_lock(&data->lock);
> > +       list_for_each_entry(notifier, &data->notifiers, list) {
> > +               notifier->ops->invalidate_start(notifier, start, end);
> > +       }
> > +       mutex_unlock(&data->lock);
> > +}
> > +
> > +static void restrictedmem_invalidate_end(struct restrictedmem_data *data,
> > +                                        pgoff_t start, pgoff_t end)
> > +{
> > +       struct restrictedmem_notifier *notifier;
> > +
> > +       mutex_lock(&data->lock);
> > +       list_for_each_entry(notifier, &data->notifiers, list) {
> > +               notifier->ops->invalidate_end(notifier, start, end);
> > +       }
> > +       mutex_unlock(&data->lock);
> > +}
> > +
> > +static void restrictedmem_notifier_error(struct restrictedmem_data *data,
> > +                                        pgoff_t start, pgoff_t end)
> > +{
> > +       struct restrictedmem_notifier *notifier;
> > +
> > +       mutex_lock(&data->lock);
> > +       list_for_each_entry(notifier, &data->notifiers, list) {
> > +               notifier->ops->error(notifier, start, end);
> > +       }
> > +       mutex_unlock(&data->lock);
> > +}
> > +
> > +static int restrictedmem_release(struct inode *inode, struct file *file)
> > +{
> > +       struct restrictedmem_data *data = inode->i_mapping->private_data;
> > +
> > +       fput(data->memfd);
> > +       kfree(data);
> > +       return 0;
> > +}
> > +
> > +static long restrictedmem_punch_hole(struct restrictedmem_data *data, int mode,
> > +                                    loff_t offset, loff_t len)
> > +{
> > +       int ret;
> > +       pgoff_t start, end;
> > +       struct file *memfd = data->memfd;
> > +
> > +       if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> > +               return -EINVAL;
> > +
> > +       start = offset >> PAGE_SHIFT;
> > +       end = (offset + len) >> PAGE_SHIFT;
> > +
> > +       restrictedmem_invalidate_start(data, start, end);
> > +       ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> > +       restrictedmem_invalidate_end(data, start, end);
> > +
> > +       return ret;
> > +}
> > +
> > +static long restrictedmem_fallocate(struct file *file, int mode,
> > +                                   loff_t offset, loff_t len)
> > +{
> > +       struct restrictedmem_data *data = file->f_mapping->private_data;
> > +       struct file *memfd = data->memfd;
> > +
> > +       if (mode & FALLOC_FL_PUNCH_HOLE)
> > +               return restrictedmem_punch_hole(data, mode, offset, len);
> > +
> > +       return memfd->f_op->fallocate(memfd, mode, offset, len);
> > +}
> > +
> > +static const struct file_operations restrictedmem_fops = {
> > +       .release = restrictedmem_release,
> > +       .fallocate = restrictedmem_fallocate,
> > +};
> > +
> > +static int restrictedmem_getattr(struct user_namespace *mnt_userns,
> > +                                const struct path *path, struct kstat *stat,
> > +                                u32 request_mask, unsigned int query_flags)
> > +{
> > +       struct inode *inode = d_inode(path->dentry);
> > +       struct restrictedmem_data *data = inode->i_mapping->private_data;
> > +       struct file *memfd = data->memfd;
> > +
> > +       return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> > +                                            request_mask, query_flags);
> > +}
> > +
> > +static int restrictedmem_setattr(struct user_namespace *mnt_userns,
> > +                                struct dentry *dentry, struct iattr *attr)
> > +{
> > +       struct inode *inode = d_inode(dentry);
> > +       struct restrictedmem_data *data = inode->i_mapping->private_data;
> > +       struct file *memfd = data->memfd;
> > +       int ret;
> > +
> > +       if (attr->ia_valid & ATTR_SIZE) {
> > +               if (memfd->f_inode->i_size)
> > +                       return -EPERM;
> > +
> > +               if (!PAGE_ALIGNED(attr->ia_size))
> > +                       return -EINVAL;
> > +       }
> > +
> > +       ret = memfd->f_inode->i_op->setattr(mnt_userns,
> > +                                           file_dentry(memfd), attr);
> > +       return ret;
> > +}
> > +
> > +static const struct inode_operations restrictedmem_iops = {
> > +       .getattr = restrictedmem_getattr,
> > +       .setattr = restrictedmem_setattr,
> > +};
> > +
> > +static int restrictedmem_init_fs_context(struct fs_context *fc)
> > +{
> > +       if (!init_pseudo(fc, RESTRICTEDMEM_MAGIC))
> > +               return -ENOMEM;
> > +
> > +       fc->s_iflags |= SB_I_NOEXEC;
> > +       return 0;
> > +}
> > +
> > +static struct file_system_type restrictedmem_fs = {
> > +       .owner          = THIS_MODULE,
> > +       .name           = "memfd:restrictedmem",
> > +       .init_fs_context = restrictedmem_init_fs_context,
> > +       .kill_sb        = kill_anon_super,
> > +};
> > +
> > +static struct vfsmount *restrictedmem_mnt;
> > +
> > +static __init int restrictedmem_init(void)
> > +{
> > +       restrictedmem_mnt = kern_mount(&restrictedmem_fs);
> > +       if (IS_ERR(restrictedmem_mnt))
> > +               return PTR_ERR(restrictedmem_mnt);
> > +       return 0;
> > +}
> > +fs_initcall(restrictedmem_init);
> > +
> > +static struct file *restrictedmem_file_create(struct file *memfd)
> > +{
> > +       struct restrictedmem_data *data;
> > +       struct address_space *mapping;
> > +       struct inode *inode;
> > +       struct file *file;
> > +
> > +       data = kzalloc(sizeof(*data), GFP_KERNEL);
> > +       if (!data)
> > +               return ERR_PTR(-ENOMEM);
> > +
> > +       data->memfd = memfd;
> > +       mutex_init(&data->lock);
> > +       INIT_LIST_HEAD(&data->notifiers);
> > +
> > +       inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
> > +       if (IS_ERR(inode)) {
> > +               kfree(data);
> > +               return ERR_CAST(inode);
> > +       }
> > +
> > +       inode->i_mode |= S_IFREG;
> > +       inode->i_op = &restrictedmem_iops;
> > +       inode->i_mapping->private_data = data;
> > +
> > +       file = alloc_file_pseudo(inode, restrictedmem_mnt,
> > +                                "restrictedmem", O_RDWR,
> > +                                &restrictedmem_fops);
> > +       if (IS_ERR(file)) {
> > +               iput(inode);
> > +               kfree(data);
> > +               return ERR_CAST(file);
> > +       }
> > +
> > +       file->f_flags |= O_LARGEFILE;
> > +
> > +       /*
> > +        * These pages are currently unmovable so don't place them into movable
> > +        * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > +        */
> > +       mapping = memfd->f_mapping;
> > +       mapping_set_unevictable(mapping);
> > +       mapping_set_gfp_mask(mapping,
> > +                            mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > +
> > +       return file;
> > +}
> > +
> > +SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> > +{
> > +       struct file *file, *restricted_file;
> > +       int fd, err;
> > +
> > +       if (flags)
> > +               return -EINVAL;
> > +
> > +       fd = get_unused_fd_flags(0);
> > +       if (fd < 0)
> > +               return fd;
> > +
> > +       file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> > +       if (IS_ERR(file)) {
> > +               err = PTR_ERR(file);
> > +               goto err_fd;
> > +       }
> > +       file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
> > +       file->f_flags |= O_LARGEFILE;
> > +
> > +       restricted_file = restrictedmem_file_create(file);
> > +       if (IS_ERR(restricted_file)) {
> > +               err = PTR_ERR(restricted_file);
> > +               fput(file);
> > +               goto err_fd;
> > +       }
> > +
> > +       fd_install(fd, restricted_file);
> > +       return fd;
> > +err_fd:
> > +       put_unused_fd(fd);
> > +       return err;
> > +}
> > +
> > +void restrictedmem_register_notifier(struct file *file,
> > +                                    struct restrictedmem_notifier *notifier)
> > +{
> > +       struct restrictedmem_data *data = file->f_mapping->private_data;
> > +
> > +       mutex_lock(&data->lock);
> > +       list_add(&notifier->list, &data->notifiers);
> > +       mutex_unlock(&data->lock);
> > +}
> > +EXPORT_SYMBOL_GPL(restrictedmem_register_notifier);
> > +
> > +void restrictedmem_unregister_notifier(struct file *file,
> > +                                      struct restrictedmem_notifier *notifier)
> > +{
> > +       struct restrictedmem_data *data = file->f_mapping->private_data;
> > +
> > +       mutex_lock(&data->lock);
> > +       list_del(&notifier->list);
> > +       mutex_unlock(&data->lock);
> > +}
> > +EXPORT_SYMBOL_GPL(restrictedmem_unregister_notifier);
> > +
> > +int restrictedmem_get_page(struct file *file, pgoff_t offset,
> > +                          struct page **pagep, int *order)
> > +{
> > +       struct restrictedmem_data *data = file->f_mapping->private_data;
> > +       struct file *memfd = data->memfd;
> > +       struct folio *folio;
> > +       struct page *page;
> > +       int ret;
> > +
> > +       ret = shmem_get_folio(file_inode(memfd), offset, &folio, SGP_WRITE);
> > +       if (ret)
> > +               return ret;
> > +
> > +       page = folio_file_page(folio, offset);
> > +       *pagep = page;
> > +       if (order)
> > +               *order = thp_order(compound_head(page));
> > +
> > +       SetPageUptodate(page);
> > +       unlock_page(page);
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(restrictedmem_get_page);
> > +
> > +void restrictedmem_error_page(struct page *page, struct address_space *mapping)
> > +{
> > +       struct super_block *sb = restrictedmem_mnt->mnt_sb;
> > +       struct inode *inode, *next;
> > +
> > +       if (!shmem_mapping(mapping))
> > +               return;
> > +
> > +       spin_lock(&sb->s_inode_list_lock);
> > +       list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> > +               struct restrictedmem_data *data = inode->i_mapping->private_data;
> > +               struct file *memfd = data->memfd;
> > +
> > +               if (memfd->f_mapping == mapping) {
> > +                       pgoff_t start, end;
> > +
> > +                       spin_unlock(&sb->s_inode_list_lock);
> > +
> > +                       start = page->index;
> > +                       end = start + thp_nr_pages(page);
> > +                       restrictedmem_notifier_error(data, start, end);
> > +                       return;
> > +               }
> > +       }
> > +       spin_unlock(&sb->s_inode_list_lock);
> > +}
> > --
> > 2.25.1
> >

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Tue, Dec 06, 2022 at 10:34:32AM -0300, Fabiano Rosas wrote:
> Chao Peng <chao.p.peng@linux.intel.com> writes:
> 
> > In confidential computing usages, whether a page is private or shared is
> > necessary information for KVM to perform operations like page fault
> > handling, page zapping etc. There are other potential use cases for
> > per-page memory attributes, e.g. to make memory read-only (or no-exec,
> > or exec-only, etc.) without having to modify memslots.
> >
> > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> > userspace to operate on the per-page memory attributes.
> >   - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
> >     a guest memory range.
> >   - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
> >     memory attributes.
> >
> > KVM internally uses xarray to store the per-page memory attributes.
> >
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> > ---
> >  Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
> >  arch/x86/kvm/Kconfig           |  1 +
> >  include/linux/kvm_host.h       |  3 ++
> >  include/uapi/linux/kvm.h       | 17 ++++++++
> >  virt/kvm/Kconfig               |  3 ++
> >  virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
> >  6 files changed, 163 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 5617bc4f899f..bb2f709c0900 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
> >  The "pad" and "reserved" fields may be used for future extensions and should be
> >  set to 0s by userspace.
> >  
> > +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> > +-----------------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm ioctl
> > +:Parameters: u64 memory attributes bitmask(out)
> > +:Returns: 0 on success, <0 on error
> > +
> > +Returns supported memory attributes bitmask. Supported memory attributes will
> > +have the corresponding bits set in u64 memory attributes bitmask.
> > +
> > +The following memory attributes are defined::
> > +
> > +  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> > +  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> > +  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> > +  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> > +
> > +4.139 KVM_SET_MEMORY_ATTRIBUTES
> > +-----------------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm ioctl
> > +:Parameters: struct kvm_memory_attributes(in/out)
> > +:Returns: 0 on success, <0 on error
> > +
> > +Sets memory attributes for pages in a guest memory range. Parameters are
> > +specified via the following structure::
> > +
> > +  struct kvm_memory_attributes {
> > +	__u64 address;
> > +	__u64 size;
> > +	__u64 attributes;
> > +	__u64 flags;
> > +  };
> > +
> > +The user sets the per-page memory attributes to a guest memory range indicated
> > +by address/size, and in return KVM adjusts address and size to reflect the
> > +actual pages of the memory range have been successfully set to the attributes.
> 
> This wording could cause some confusion, what about a simpler:
> 
> "reflect the range of pages that had its attributes successfully set"

Thanks, this is much better.

> 
> > +If the call returns 0, "address" is updated to the last successful address + 1
> > +and "size" is updated to the remaining address size that has not been set
> > +successfully.
> 
> "address + 1 page" or "subsequent page" perhaps.
> 
> In fact, wouldn't this all become simpler if size were number of pages instead?

It indeed becomes better if the size is number of pages and the address
is gfn, but I think we don't want to imply that the page size is 4K to
userspace.

> 
> > The user should check the return value as well as the size to
> > +decide if the operation succeeded for the whole range or not. The user may want
> > +to retry the operation with the returned address/size if the previous range was
> > +partially successful.
> > +
> > +Both address and size should be page aligned and the supported attributes can be
> > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> > +
> > +The "flags" field may be used for future extensions and should be set to 0s.
> > +
> 
> ...
> 
> > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > +					   struct kvm_memory_attributes *attrs)
> > +{
> > +	gfn_t start, end;
> > +	unsigned long i;
> > +	void *entry;
> > +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +	/* flags is currently not used. */
> > +	if (attrs->flags)
> > +		return -EINVAL;
> > +	if (attrs->attributes & ~supported_attrs)
> > +		return -EINVAL;
> > +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > +		return -EINVAL;
> > +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > +		return -EINVAL;
> > +
> > +	start = attrs->address >> PAGE_SHIFT;
> > +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> 
> Here PAGE_SIZE and -1 cancel out.

Correct!

> 
> Consider using gpa_to_gfn as well.

Yes using gpa_to_gfn is appropriate.

Thanks,
Chao
> 
> > +
> > +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > +
> > +	mutex_lock(&kvm->lock);
> > +	for (i = start; i < end; i++)
> > +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > +				    GFP_KERNEL_ACCOUNT)))
> > +			break;
> > +	mutex_unlock(&kvm->lock);
> > +
> > +	attrs->address = i << PAGE_SHIFT;
> > +	attrs->size = (end - i) << PAGE_SHIFT;
> > +
> > +	return 0;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > +
> >  struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
> >  {
> >  	return __gfn_to_memslot(kvm_memslots(kvm), gfn);
> > @@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
> >  #ifdef CONFIG_HAVE_KVM_MSI
> >  	case KVM_CAP_SIGNAL_MSI:
> >  #endif
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +	case KVM_CAP_MEMORY_ATTRIBUTES:
> > +#endif
> >  #ifdef CONFIG_HAVE_KVM_IRQFD
> >  	case KVM_CAP_IRQFD:
> >  	case KVM_CAP_IRQFD_RESAMPLE:
> > @@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp,
> >  		break;
> >  	}
> >  #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +	case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: {
> > +		u64 attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +		r = -EFAULT;
> > +		if (copy_to_user(argp, &attrs, sizeof(attrs)))
> > +			goto out;
> > +		r = 0;
> > +		break;
> > +	}
> > +	case KVM_SET_MEMORY_ATTRIBUTES: {
> > +		struct kvm_memory_attributes attrs;
> > +
> > +		r = -EFAULT;
> > +		if (copy_from_user(&attrs, argp, sizeof(attrs)))
> > +			goto out;
> > +
> > +		r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);
> > +
> > +		if (!r && copy_to_user(argp, &attrs, sizeof(attrs)))
> > +			r = -EFAULT;
> > +		break;
> > +	}
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> >  	case KVM_CREATE_DEVICE: {
> >  		struct kvm_create_device cd;

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Tue, Dec 06, 2022 at 03:07:27PM +0000, Fuad Tabba wrote:
> Hi,
> 
> On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > In confidential computing usages, whether a page is private or shared is
> > necessary information for KVM to perform operations like page fault
> > handling, page zapping etc. There are other potential use cases for
> > per-page memory attributes, e.g. to make memory read-only (or no-exec,
> > or exec-only, etc.) without having to modify memslots.
> >
> > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> > userspace to operate on the per-page memory attributes.
> >   - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
> >     a guest memory range.
> >   - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
> >     memory attributes.
> >
> > KVM internally uses xarray to store the per-page memory attributes.
> >
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> > ---
> >  Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
> >  arch/x86/kvm/Kconfig           |  1 +
> >  include/linux/kvm_host.h       |  3 ++
> >  include/uapi/linux/kvm.h       | 17 ++++++++
> >  virt/kvm/Kconfig               |  3 ++
> >  virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
> >  6 files changed, 163 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 5617bc4f899f..bb2f709c0900 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
> >  The "pad" and "reserved" fields may be used for future extensions and should be
> >  set to 0s by userspace.
> >
> > +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> > +-----------------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm ioctl
> > +:Parameters: u64 memory attributes bitmask(out)
> > +:Returns: 0 on success, <0 on error
> > +
> > +Returns supported memory attributes bitmask. Supported memory attributes will
> > +have the corresponding bits set in u64 memory attributes bitmask.
> > +
> > +The following memory attributes are defined::
> > +
> > +  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> > +  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> > +  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> > +  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> > +
> > +4.139 KVM_SET_MEMORY_ATTRIBUTES
> > +-----------------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm ioctl
> > +:Parameters: struct kvm_memory_attributes(in/out)
> > +:Returns: 0 on success, <0 on error
> > +
> > +Sets memory attributes for pages in a guest memory range. Parameters are
> > +specified via the following structure::
> > +
> > +  struct kvm_memory_attributes {
> > +       __u64 address;
> > +       __u64 size;
> > +       __u64 attributes;
> > +       __u64 flags;
> > +  };
> > +
> > +The user sets the per-page memory attributes to a guest memory range indicated
> > +by address/size, and in return KVM adjusts address and size to reflect the
> > +actual pages of the memory range have been successfully set to the attributes.
> > +If the call returns 0, "address" is updated to the last successful address + 1
> > +and "size" is updated to the remaining address size that has not been set
> > +successfully. The user should check the return value as well as the size to
> > +decide if the operation succeeded for the whole range or not. The user may want
> > +to retry the operation with the returned address/size if the previous range was
> > +partially successful.
> > +
> > +Both address and size should be page aligned and the supported attributes can be
> > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> > +
> > +The "flags" field may be used for future extensions and should be set to 0s.
> > +
> >  5. The kvm_run structure
> >  ========================
> >
> > @@ -8270,6 +8323,16 @@ structure.
> >  When getting the Modified Change Topology Report value, the attr->addr
> >  must point to a byte where the value will be stored or retrieved from.
> >
> > +8.40 KVM_CAP_MEMORY_ATTRIBUTES
> > +------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm
> > +
> > +This capability indicates KVM supports per-page memory attributes and ioctls
> > +KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available.
> > +
> >  9. Known KVM API problems
> >  =========================
> >
> > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > index fbeaa9ddef59..a8e379a3afee 100644
> > --- a/arch/x86/kvm/Kconfig
> > +++ b/arch/x86/kvm/Kconfig
> > @@ -49,6 +49,7 @@ config KVM
> >         select SRCU
> >         select INTERVAL_TREE
> >         select HAVE_KVM_PM_NOTIFIER if PM
> > +       select HAVE_KVM_MEMORY_ATTRIBUTES
> >         help
> >           Support hosting fully virtualized guest machines using hardware
> >           virtualization extensions.  You will need a fairly recent
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 8f874a964313..a784e2b06625 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -800,6 +800,9 @@ struct kvm {
> >
> >  #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
> >         struct notifier_block pm_notifier;
> > +#endif
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +       struct xarray mem_attr_array;
> >  #endif
> >         char stats_id[KVM_STATS_NAME_SIZE];
> >  };
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index 64dfe9c07c87..5d0941acb5bb 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -1182,6 +1182,7 @@ struct kvm_ppc_resize_hpt {
> >  #define KVM_CAP_S390_CPU_TOPOLOGY 222
> >  #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
> >  #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
> > +#define KVM_CAP_MEMORY_ATTRIBUTES 225
> >
> >  #ifdef KVM_CAP_IRQ_ROUTING
> >
> > @@ -2238,4 +2239,20 @@ struct kvm_s390_zpci_op {
> >  /* flags for kvm_s390_zpci_op->u.reg_aen.flags */
> >  #define KVM_S390_ZPCIOP_REGAEN_HOST    (1 << 0)
> >
> > +/* Available with KVM_CAP_MEMORY_ATTRIBUTES */
> > +#define KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES    _IOR(KVMIO,  0xd2, __u64)
> > +#define KVM_SET_MEMORY_ATTRIBUTES              _IOWR(KVMIO,  0xd3, struct kvm_memory_attributes)
> > +
> > +struct kvm_memory_attributes {
> > +       __u64 address;
> > +       __u64 size;
> > +       __u64 attributes;
> > +       __u64 flags;
> > +};
> > +
> > +#define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> > +#define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> > +#define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> > +#define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> 
> nit: how about using the BIT() macro for these?

Might be the _BITULL() in include/uapi/linux/const.h since it will be
used by userspace also.

> 
> > +
> >  #endif /* __LINUX_KVM_H */
> > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> > index 800f9470e36b..effdea5dd4f0 100644
> > --- a/virt/kvm/Kconfig
> > +++ b/virt/kvm/Kconfig
> > @@ -19,6 +19,9 @@ config HAVE_KVM_IRQ_ROUTING
> >  config HAVE_KVM_DIRTY_RING
> >         bool
> >
> > +config HAVE_KVM_MEMORY_ATTRIBUTES
> > +       bool
> > +
> >  # Only strongly ordered architectures can select this, as it doesn't
> >  # put any explicit constraint on userspace ordering. They can also
> >  # select the _ACQ_REL version.
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 1782c4555d94..7f0f5e9f2406 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> >         spin_lock_init(&kvm->mn_invalidate_lock);
> >         rcuwait_init(&kvm->mn_memslots_update_rcuwait);
> >         xa_init(&kvm->vcpu_array);
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +       xa_init(&kvm->mem_attr_array);
> > +#endif
> >
> >         INIT_LIST_HEAD(&kvm->gpc_list);
> >         spin_lock_init(&kvm->gpc_lock);
> > @@ -1323,6 +1326,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
> >                 kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
> >                 kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
> >         }
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +       xa_destroy(&kvm->mem_attr_array);
> > +#endif
> >         cleanup_srcu_struct(&kvm->irq_srcu);
> >         cleanup_srcu_struct(&kvm->srcu);
> >         kvm_arch_free_vm(kvm);
> > @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
> >  }
> >  #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
> >
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> > +{
> > +       return 0;
> > +}
> > +
> > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > +                                          struct kvm_memory_attributes *attrs)
> > +{
> > +       gfn_t start, end;
> > +       unsigned long i;
> > +       void *entry;
> > +       u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +       /* flags is currently not used. */
> 
> nit: "is reserved"? I think it makes it a bit clearer what its purpose is.
OK, then:
  flags is reserved for future extention and currently is not used.

> 
> > +       if (attrs->flags)
> > +               return -EINVAL;
> > +       if (attrs->attributes & ~supported_attrs)
> > +               return -EINVAL;
> > +       if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > +               return -EINVAL;
> > +       if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > +               return -EINVAL;
> > +
> > +       start = attrs->address >> PAGE_SHIFT;
> > +       end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> 
> Would using existing helpers be better for getting the frame numbers?

Yes, gpa_to_gfn() can be used.

> Also, the code checks that the address and size are page aligned, so
> the end rounding up seems redundant, and might even be wrong if the
> address+size-1 is close to the gfn_t limit (which this code tries to
> avoid in an earlier check).

That's right.

> 
> > +       entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > +
> > +       mutex_lock(&kvm->lock);
> > +       for (i = start; i < end; i++)
> > +               if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > +                                   GFP_KERNEL_ACCOUNT)))
> > +                       break;
> > +       mutex_unlock(&kvm->lock);
> > +
> > +       attrs->address = i << PAGE_SHIFT;
> > +       attrs->size = (end - i) << PAGE_SHIFT;
> 
> nit: helpers for these too?

Similarly, gfn_to_gpa() will be used.

> 
> With the end calculation fixed,
> 
> Reviewed-by: Fuad Tabba <tabba@google.com>
> After adding the necessary configs for arm64 (on qemu/arm64):
> Tested-by: Fuad Tabba <tabba@google.com>

Thanks.
Chao
> 
> Cheers,
> /fuad
> 
> > +
> > +       return 0;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > +
> >  struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
> >  {
> >         return __gfn_to_memslot(kvm_memslots(kvm), gfn);
> > @@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
> >  #ifdef CONFIG_HAVE_KVM_MSI
> >         case KVM_CAP_SIGNAL_MSI:
> >  #endif
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +       case KVM_CAP_MEMORY_ATTRIBUTES:
> > +#endif
> >  #ifdef CONFIG_HAVE_KVM_IRQFD
> >         case KVM_CAP_IRQFD:
> >         case KVM_CAP_IRQFD_RESAMPLE:
> > @@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp,
> >                 break;
> >         }
> >  #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +       case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: {
> > +               u64 attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +               r = -EFAULT;
> > +               if (copy_to_user(argp, &attrs, sizeof(attrs)))
> > +                       goto out;
> > +               r = 0;
> > +               break;
> > +       }
> > +       case KVM_SET_MEMORY_ATTRIBUTES: {
> > +               struct kvm_memory_attributes attrs;
> > +
> > +               r = -EFAULT;
> > +               if (copy_from_user(&attrs, argp, sizeof(attrs)))
> > +                       goto out;
> > +
> > +               r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);
> > +
> > +               if (!r && copy_to_user(argp, &attrs, sizeof(attrs)))
> > +                       r = -EFAULT;
> > +               break;
> > +       }
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> >         case KVM_CREATE_DEVICE: {
> >                 struct kvm_create_device cd;
> >
> > --
> > 2.25.1
> >

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Tue, Dec 06, 2022 at 12:39:18PM +0000, Fuad Tabba wrote:
> Hi Chao,
> 
> On Tue, Dec 6, 2022 at 11:58 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > On Mon, Dec 05, 2022 at 09:03:11AM +0000, Fuad Tabba wrote:
> > > Hi Chao,
> > >
> > > On Fri, Dec 2, 2022 at 6:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > > >
> > > > In memory encryption usage, guest memory may be encrypted with special
> > > > key and can be accessed only by the guest itself. We call such memory
> > > > private memory. It's valueless and sometimes can cause problem to allow
> > > > userspace to access guest private memory. This new KVM memslot extension
> > > > allows guest private memory being provided through a restrictedmem
> > > > backed file descriptor(fd) and userspace is restricted to access the
> > > > bookmarked memory in the fd.
> > > >
> > > > This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> > > > additional KVM memslot fields restricted_fd/restricted_offset to allow
> > > > userspace to instruct KVM to provide guest memory through restricted_fd.
> > > > 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> > > > and the size is 'memory_size'.
> > > >
> > > > The extended memslot can still have the userspace_addr(hva). When use, a
> > > > single memslot can maintain both private memory through restricted_fd
> > > > and shared memory through userspace_addr. Whether the private or shared
> > > > part is visible to guest is maintained by other KVM code.
> > > >
> > > > A restrictedmem_notifier field is also added to the memslot structure to
> > > > allow the restricted_fd's backing store to notify KVM the memory change,
> > > > KVM then can invalidate its page table entries or handle memory errors.
> > > >
> > > > Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> > > > and right now it is selected on X86_64 only.
> > > >
> > > > To make future maintenance easy, internally use a binary compatible
> > > > alias struct kvm_user_mem_region to handle both the normal and the
> > > > '_ext' variants.
> > > >
> > > > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > > Reviewed-by: Fuad Tabba <tabba@google.com>
> > > > Tested-by: Fuad Tabba <tabba@google.com>
> > >
> > > V9 of this patch [*] had KVM_CAP_PRIVATE_MEM, but it's not in this
> > > patch series anymore. Any reason you removed it, or is it just an
> > > omission?
> >
> > We had some discussion in v9 [1] to add generic memory attributes ioctls
> > and KVM_CAP_PRIVATE_MEM can be implemented as a new
> > KVM_MEMORY_ATTRIBUTE_PRIVATE flag via KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES()
> > ioctl [2]. The api doc has been updated:
> >
> > +- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
> > +  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl) …
> >
> >
> > [1] https://lore.kernel.org/linux-mm/Y2WB48kD0J4VGynX@google.com/
> > [2]
> > https://lore.kernel.org/linux-mm/20221202061347.1070246-3-chao.p.peng@linux.intel.com/
> 
> I see. I just retested it with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES,
> and my Reviewed/Tested-by still apply.

Thanks for the info.

Chao
> 
> Cheers,
> /fuad
> 
> >
> > Thanks,
> > Chao
> > >
> > > [*] https://lore.kernel.org/linux-mm/20221025151344.3784230-3-chao.p.peng@linux.intel.com/
> > >
> > > Thanks,
> > > /fuad
> > >
> > > > ---
> > > >  Documentation/virt/kvm/api.rst | 40 ++++++++++++++++++++++-----
> > > >  arch/x86/kvm/Kconfig           |  2 ++
> > > >  arch/x86/kvm/x86.c             |  2 +-
> > > >  include/linux/kvm_host.h       |  8 ++++--
> > > >  include/uapi/linux/kvm.h       | 28 +++++++++++++++++++
> > > >  virt/kvm/Kconfig               |  3 +++
> > > >  virt/kvm/kvm_main.c            | 49 ++++++++++++++++++++++++++++------
> > > >  7 files changed, 114 insertions(+), 18 deletions(-)
> > > >
> > > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > > > index bb2f709c0900..99352170c130 100644
> > > > --- a/Documentation/virt/kvm/api.rst
> > > > +++ b/Documentation/virt/kvm/api.rst
> > > > @@ -1319,7 +1319,7 @@ yet and must be cleared on entry.
> > > >  :Capability: KVM_CAP_USER_MEMORY
> > > >  :Architectures: all
> > > >  :Type: vm ioctl
> > > > -:Parameters: struct kvm_userspace_memory_region (in)
> > > > +:Parameters: struct kvm_userspace_memory_region(_ext) (in)
> > > >  :Returns: 0 on success, -1 on error
> > > >
> > > >  ::
> > > > @@ -1332,9 +1332,18 @@ yet and must be cleared on entry.
> > > >         __u64 userspace_addr; /* start of the userspace allocated memory */
> > > >    };
> > > >
> > > > +  struct kvm_userspace_memory_region_ext {
> > > > +       struct kvm_userspace_memory_region region;
> > > > +       __u64 restricted_offset;
> > > > +       __u32 restricted_fd;
> > > > +       __u32 pad1;
> > > > +       __u64 pad2[14];
> > > > +  };
> > > > +
> > > >    /* for kvm_memory_region::flags */
> > > >    #define KVM_MEM_LOG_DIRTY_PAGES      (1UL << 0)
> > > >    #define KVM_MEM_READONLY     (1UL << 1)
> > > > +  #define KVM_MEM_PRIVATE              (1UL << 2)
> > > >
> > > >  This ioctl allows the user to create, modify or delete a guest physical
> > > >  memory slot.  Bits 0-15 of "slot" specify the slot id and this value
> > > > @@ -1365,12 +1374,29 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
> > > >  be identical.  This allows large pages in the guest to be backed by large
> > > >  pages in the host.
> > > >
> > > > -The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
> > > > -KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
> > > > -writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
> > > > -use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
> > > > -to make a new slot read-only.  In this case, writes to this memory will be
> > > > -posted to userspace as KVM_EXIT_MMIO exits.
> > > > +kvm_userspace_memory_region_ext struct includes all fields of
> > > > +kvm_userspace_memory_region struct, while also adds additional fields for some
> > > > +other features. See below description of flags field for more information.
> > > > +It's recommended to use kvm_userspace_memory_region_ext in new userspace code.
> > > > +
> > > > +The flags field supports following flags:
> > > > +
> > > > +- KVM_MEM_LOG_DIRTY_PAGES to instruct KVM to keep track of writes to memory
> > > > +  within the slot. For more details, see KVM_GET_DIRTY_LOG ioctl.
> > > > +
> > > > +- KVM_MEM_READONLY, if KVM_CAP_READONLY_MEM allows, to make a new slot
> > > > +  read-only. In this case, writes to this memory will be posted to userspace as
> > > > +  KVM_EXIT_MMIO exits.
> > > > +
> > > > +- KVM_MEM_PRIVATE, if KVM_MEMORY_ATTRIBUTE_PRIVATE is supported (see
> > > > +  KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES ioctl), to indicate a new slot has private
> > > > +  memory backed by a file descriptor(fd) and userspace access to the fd may be
> > > > +  restricted. Userspace should use restricted_fd/restricted_offset in the
> > > > +  kvm_userspace_memory_region_ext to instruct KVM to provide private memory
> > > > +  to guest. Userspace should guarantee not to map the same host physical address
> > > > +  indicated by restricted_fd/restricted_offset to different guest physical
> > > > +  addresses within multiple memslots. Failed to do this may result undefined
> > > > +  behavior.
> > > >
> > > >  When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
> > > >  the memory region are automatically reflected into the guest.  For example, an
> > > > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > > > index a8e379a3afee..690cb21010e7 100644
> > > > --- a/arch/x86/kvm/Kconfig
> > > > +++ b/arch/x86/kvm/Kconfig
> > > > @@ -50,6 +50,8 @@ config KVM
> > > >         select INTERVAL_TREE
> > > >         select HAVE_KVM_PM_NOTIFIER if PM
> > > >         select HAVE_KVM_MEMORY_ATTRIBUTES
> > > > +       select HAVE_KVM_RESTRICTED_MEM if X86_64
> > > > +       select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
> > > >         help
> > > >           Support hosting fully virtualized guest machines using hardware
> > > >           virtualization extensions.  You will need a fairly recent
> > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > > index 7f850dfb4086..9a07380f8d3c 100644
> > > > --- a/arch/x86/kvm/x86.c
> > > > +++ b/arch/x86/kvm/x86.c
> > > > @@ -12224,7 +12224,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
> > > >         }
> > > >
> > > >         for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > > > -               struct kvm_userspace_memory_region m;
> > > > +               struct kvm_user_mem_region m;
> > > >
> > > >                 m.slot = id | (i << 16);
> > > >                 m.flags = 0;
> > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > > index a784e2b06625..02347e386ea2 100644
> > > > --- a/include/linux/kvm_host.h
> > > > +++ b/include/linux/kvm_host.h
> > > > @@ -44,6 +44,7 @@
> > > >
> > > >  #include <asm/kvm_host.h>
> > > >  #include <linux/kvm_dirty_ring.h>
> > > > +#include <linux/restrictedmem.h>
> > > >
> > > >  #ifndef KVM_MAX_VCPU_IDS
> > > >  #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
> > > > @@ -585,6 +586,9 @@ struct kvm_memory_slot {
> > > >         u32 flags;
> > > >         short id;
> > > >         u16 as_id;
> > > > +       struct file *restricted_file;
> > > > +       loff_t restricted_offset;
> > > > +       struct restrictedmem_notifier notifier;
> > > >  };
> > > >
> > > >  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
> > > > @@ -1123,9 +1127,9 @@ enum kvm_mr_change {
> > > >  };
> > > >
> > > >  int kvm_set_memory_region(struct kvm *kvm,
> > > > -                         const struct kvm_userspace_memory_region *mem);
> > > > +                         const struct kvm_user_mem_region *mem);
> > > >  int __kvm_set_memory_region(struct kvm *kvm,
> > > > -                           const struct kvm_userspace_memory_region *mem);
> > > > +                           const struct kvm_user_mem_region *mem);
> > > >  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
> > > >  void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
> > > >  int kvm_arch_prepare_memory_region(struct kvm *kvm,
> > > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > > > index 5d0941acb5bb..13bff963b8b0 100644
> > > > --- a/include/uapi/linux/kvm.h
> > > > +++ b/include/uapi/linux/kvm.h
> > > > @@ -103,6 +103,33 @@ struct kvm_userspace_memory_region {
> > > >         __u64 userspace_addr; /* start of the userspace allocated memory */
> > > >  };
> > > >
> > > > +struct kvm_userspace_memory_region_ext {
> > > > +       struct kvm_userspace_memory_region region;
> > > > +       __u64 restricted_offset;
> > > > +       __u32 restricted_fd;
> > > > +       __u32 pad1;
> > > > +       __u64 pad2[14];
> > > > +};
> > > > +
> > > > +#ifdef __KERNEL__
> > > > +/*
> > > > + * kvm_user_mem_region is a kernel-only alias of kvm_userspace_memory_region_ext
> > > > + * that "unpacks" kvm_userspace_memory_region so that KVM can directly access
> > > > + * all fields from the top-level "extended" region.
> > > > + */
> > > > +struct kvm_user_mem_region {
> > > > +       __u32 slot;
> > > > +       __u32 flags;
> > > > +       __u64 guest_phys_addr;
> > > > +       __u64 memory_size;
> > > > +       __u64 userspace_addr;
> > > > +       __u64 restricted_offset;
> > > > +       __u32 restricted_fd;
> > > > +       __u32 pad1;
> > > > +       __u64 pad2[14];
> > > > +};
> > > > +#endif
> > > > +
> > > >  /*
> > > >   * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
> > > >   * other bits are reserved for kvm internal use which are defined in
> > > > @@ -110,6 +137,7 @@ struct kvm_userspace_memory_region {
> > > >   */
> > > >  #define KVM_MEM_LOG_DIRTY_PAGES        (1UL << 0)
> > > >  #define KVM_MEM_READONLY       (1UL << 1)
> > > > +#define KVM_MEM_PRIVATE                (1UL << 2)
> > > >
> > > >  /* for KVM_IRQ_LINE */
> > > >  struct kvm_irq_level {
> > > > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> > > > index effdea5dd4f0..d605545d6dd1 100644
> > > > --- a/virt/kvm/Kconfig
> > > > +++ b/virt/kvm/Kconfig
> > > > @@ -89,3 +89,6 @@ config KVM_XFER_TO_GUEST_WORK
> > > >
> > > >  config HAVE_KVM_PM_NOTIFIER
> > > >         bool
> > > > +
> > > > +config HAVE_KVM_RESTRICTED_MEM
> > > > +       bool
> > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > > index 7f0f5e9f2406..b882eb2c76a2 100644
> > > > --- a/virt/kvm/kvm_main.c
> > > > +++ b/virt/kvm/kvm_main.c
> > > > @@ -1532,7 +1532,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
> > > >         }
> > > >  }
> > > >
> > > > -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
> > > > +static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> > > >  {
> > > >         u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> > > >
> > > > @@ -1934,7 +1934,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
> > > >   * Must be called holding kvm->slots_lock for write.
> > > >   */
> > > >  int __kvm_set_memory_region(struct kvm *kvm,
> > > > -                           const struct kvm_userspace_memory_region *mem)
> > > > +                           const struct kvm_user_mem_region *mem)
> > > >  {
> > > >         struct kvm_memory_slot *old, *new;
> > > >         struct kvm_memslots *slots;
> > > > @@ -2038,7 +2038,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > > >  EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> > > >
> > > >  int kvm_set_memory_region(struct kvm *kvm,
> > > > -                         const struct kvm_userspace_memory_region *mem)
> > > > +                         const struct kvm_user_mem_region *mem)
> > > >  {
> > > >         int r;
> > > >
> > > > @@ -2050,7 +2050,7 @@ int kvm_set_memory_region(struct kvm *kvm,
> > > >  EXPORT_SYMBOL_GPL(kvm_set_memory_region);
> > > >
> > > >  static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
> > > > -                                         struct kvm_userspace_memory_region *mem)
> > > > +                                         struct kvm_user_mem_region *mem)
> > > >  {
> > > >         if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
> > > >                 return -EINVAL;
> > > > @@ -4698,6 +4698,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
> > > >         return fd;
> > > >  }
> > > >
> > > > +#define SANITY_CHECK_MEM_REGION_FIELD(field)                                   \
> > > > +do {                                                                           \
> > > > +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=             \
> > > > +                    offsetof(struct kvm_userspace_memory_region, field));      \
> > > > +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=         \
> > > > +                    sizeof_field(struct kvm_userspace_memory_region, field));  \
> > > > +} while (0)
> > > > +
> > > > +#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)                                       \
> > > > +do {                                                                                   \
> > > > +       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=                     \
> > > > +                    offsetof(struct kvm_userspace_memory_region_ext, field));          \
> > > > +       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=                 \
> > > > +                    sizeof_field(struct kvm_userspace_memory_region_ext, field));      \
> > > > +} while (0)
> > > > +
> > > > +static void kvm_sanity_check_user_mem_region_alias(void)
> > > > +{
> > > > +       SANITY_CHECK_MEM_REGION_FIELD(slot);
> > > > +       SANITY_CHECK_MEM_REGION_FIELD(flags);
> > > > +       SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
> > > > +       SANITY_CHECK_MEM_REGION_FIELD(memory_size);
> > > > +       SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
> > > > +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_offset);
> > > > +       SANITY_CHECK_MEM_REGION_EXT_FIELD(restricted_fd);
> > > > +}
> > > > +
> > > >  static long kvm_vm_ioctl(struct file *filp,
> > > >                            unsigned int ioctl, unsigned long arg)
> > > >  {
> > > > @@ -4721,14 +4748,20 @@ static long kvm_vm_ioctl(struct file *filp,
> > > >                 break;
> > > >         }
> > > >         case KVM_SET_USER_MEMORY_REGION: {
> > > > -               struct kvm_userspace_memory_region kvm_userspace_mem;
> > > > +               struct kvm_user_mem_region mem;
> > > > +               unsigned long size = sizeof(struct kvm_userspace_memory_region);
> > > > +
> > > > +               kvm_sanity_check_user_mem_region_alias();
> > > >
> > > >                 r = -EFAULT;
> > > > -               if (copy_from_user(&kvm_userspace_mem, argp,
> > > > -                                               sizeof(kvm_userspace_mem)))
> > > > +               if (copy_from_user(&mem, argp, size))
> > > > +                       goto out;
> > > > +
> > > > +               r = -EINVAL;
> > > > +               if (mem.flags & KVM_MEM_PRIVATE)
> > > >                         goto out;
> > > >
> > > > -               r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
> > > > +               r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> > > >                 break;
> > > >         }
> > > >         case KVM_GET_DIRTY_LOG: {
> > > > --
> > > > 2.25.1
> > > >

Re: [PATCH v10 4/9] KVM: Add KVM_EXIT_MEMORY_FAULT exit

[Chao Peng]

On Tue, Dec 06, 2022 at 03:47:20PM +0000, Fuad Tabba wrote:
> Hi,
> 
> On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > This new KVM exit allows userspace to handle memory-related errors. It
> > indicates an error happens in KVM at guest memory range [gpa, gpa+size).
> > The flags includes additional information for userspace to handle the
> > error. Currently bit 0 is defined as 'private memory' where '1'
> > indicates error happens due to private memory access and '0' indicates
> > error happens due to shared memory access.
> >
> > When private memory is enabled, this new exit will be used for KVM to
> > exit to userspace for shared <-> private memory conversion in memory
> > encryption usage. In such usage, typically there are two kind of memory
> > conversions:
> >   - explicit conversion: happens when guest explicitly calls into KVM
> >     to map a range (as private or shared), KVM then exits to userspace
> >     to perform the map/unmap operations.
> >   - implicit conversion: happens in KVM page fault handler where KVM
> >     exits to userspace for an implicit conversion when the page is in a
> >     different state than requested (private or shared).
> >
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > Reviewed-by: Fuad Tabba <tabba@google.com>
> > ---
> >  Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++++
> >  include/uapi/linux/kvm.h       |  8 ++++++++
> >  2 files changed, 30 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 99352170c130..d9edb14ce30b 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -6634,6 +6634,28 @@ array field represents return values. The userspace should update the return
> >  values of SBI call before resuming the VCPU. For more details on RISC-V SBI
> >  spec refer, https://github.com/riscv/riscv-sbi-doc.
> >
> > +::
> > +
> > +               /* KVM_EXIT_MEMORY_FAULT */
> > +               struct {
> > +  #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 0)
> > +                       __u64 flags;
> 
> I see you've removed the padding and increased the flag size.

Yes Sean suggested this and also looks good to me.

Chao
> 
> Reviewed-by: Fuad Tabba <tabba@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>
> 
> Cheers,
> /fuad
> 
> 
> 
> 
> > +                       __u64 gpa;
> > +                       __u64 size;
> > +               } memory;
> > +
> > +If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has
> > +encountered a memory error which is not handled by KVM kernel module and
> > +userspace may choose to handle it. The 'flags' field indicates the memory
> > +properties of the exit.
> > +
> > + - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by
> > +   private memory access when the bit is set. Otherwise the memory error is
> > +   caused by shared memory access when the bit is clear.
> > +
> > +'gpa' and 'size' indicate the memory range the error occurs at. The userspace
> > +may handle the error and return to KVM to retry the previous memory access.
> > +
> >  ::
> >
> >      /* KVM_EXIT_NOTIFY */
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index 13bff963b8b0..c7e9d375a902 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -300,6 +300,7 @@ struct kvm_xen_exit {
> >  #define KVM_EXIT_RISCV_SBI        35
> >  #define KVM_EXIT_RISCV_CSR        36
> >  #define KVM_EXIT_NOTIFY           37
> > +#define KVM_EXIT_MEMORY_FAULT     38
> >
> >  /* For KVM_EXIT_INTERNAL_ERROR */
> >  /* Emulate instruction failed. */
> > @@ -541,6 +542,13 @@ struct kvm_run {
> >  #define KVM_NOTIFY_CONTEXT_INVALID     (1 << 0)
> >                         __u32 flags;
> >                 } notify;
> > +               /* KVM_EXIT_MEMORY_FAULT */
> > +               struct {
> > +#define KVM_MEMORY_EXIT_FLAG_PRIVATE   (1ULL << 0)
> > +                       __u64 flags;
> > +                       __u64 gpa;
> > +                       __u64 size;
> > +               } memory;
> >                 /* Fix the size of the union. */
> >                 char padding[256];
> >         };
> > --
> > 2.25.1
> >

Re: [PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry

[Chao Peng]

On Tue, Dec 06, 2022 at 10:34:11PM -0800, Isaku Yamahata wrote:
> On Tue, Dec 06, 2022 at 07:56:23PM +0800,
> Chao Peng <chao.p.peng@linux.intel.com> wrote:
> 
> > > > -       if (unlikely(kvm->mmu_invalidate_in_progress) &&
> > > > -           hva >= kvm->mmu_invalidate_range_start &&
> > > > -           hva < kvm->mmu_invalidate_range_end)
> > > > -               return 1;
> > > > +       if (unlikely(kvm->mmu_invalidate_in_progress)) {
> > > > +               /*
> > > > +                * Dropping mmu_lock after bumping mmu_invalidate_in_progress
> > > > +                * but before updating the range is a KVM bug.
> > > > +                */
> > > > +               if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
> > > > +                                kvm->mmu_invalidate_range_end == INVALID_GPA))
> > > 
> > > INVALID_GPA is an x86-specific define in
> > > arch/x86/include/asm/kvm_host.h, so this doesn't build on other
> > > architectures. The obvious fix is to move it to
> > > include/linux/kvm_host.h.
> > 
> > Hmm, INVALID_GPA is defined as ZERO for x86, not 100% confident this is
> > correct choice for other architectures, but after search it has not been
> > used for other architectures, so should be safe to make it common.
> 
> INVALID_GPA is defined as all bit 1.  Please notice "~" (tilde).
> 
> #define INVALID_GPA (~(gpa_t)0)

Thanks for mention. Still looks right moving it to include/linux/kvm_host.h. 
Chao
> -- 
> Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Fuad Tabba]

Hi,

On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> Unmap the existing guest mappings when memory attribute is changed
> between shared and private. This is needed because shared pages and
> private pages are from different backends, unmapping existing ones
> gives a chance for page fault handler to re-populate the mappings
> according to the new attribute.
>
> Only architecture has private memory support needs this and the
> supported architecture is expected to rewrite the weak
> kvm_arch_has_private_mem().

This kind of ties into the discussion of being able to share memory in
place. For pKVM for example, shared and private memory would have the
same backend, and the unmapping wouldn't be needed.

So I guess that, instead of kvm_arch_has_private_mem(), can the check
be done differently, e.g., with a different function, say
kvm_arch_private_notify_attribute_change() (but maybe with a more
friendly name than what I suggested :) )?

Thanks,
/fuad

>
> Also, during memory attribute changing and the unmapping time frame,
> page fault handler may happen in the same memory range and can cause
> incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> page fault handler retry during this time frame.
>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  include/linux/kvm_host.h |   7 +-
>  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
>  2 files changed, 116 insertions(+), 59 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3d69484d2704..3331c0c92838 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
>  #endif
>
> -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
>  struct kvm_gfn_range {
>         struct kvm_memory_slot *slot;
>         gfn_t start;
> @@ -264,6 +263,8 @@ struct kvm_gfn_range {
>         bool may_block;
>  };
>  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> +
> +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
>  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> @@ -785,11 +786,12 @@ struct kvm {
>
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>         struct mmu_notifier mmu_notifier;
> +#endif
>         unsigned long mmu_invalidate_seq;
>         long mmu_invalidate_in_progress;
>         gfn_t mmu_invalidate_range_start;
>         gfn_t mmu_invalidate_range_end;
> -#endif
> +
>         struct list_head devices;
>         u64 manual_dirty_log_protect;
>         struct dentry *debugfs_dentry;
> @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
>  int kvm_arch_post_init_vm(struct kvm *kvm);
>  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
>  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> +bool kvm_arch_has_private_mem(struct kvm *kvm);
>
>  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
>  /*
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index ad55dfbc75d7..4e1e1e113bf0 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
>  }
>  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
>
> +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> +{
> +       /*
> +        * The count increase must become visible at unlock time as no
> +        * spte can be established without taking the mmu_lock and
> +        * count is also read inside the mmu_lock critical section.
> +        */
> +       kvm->mmu_invalidate_in_progress++;
> +
> +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +               kvm->mmu_invalidate_range_start = INVALID_GPA;
> +               kvm->mmu_invalidate_range_end = INVALID_GPA;
> +       }
> +}
> +
> +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> +
> +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +               kvm->mmu_invalidate_range_start = start;
> +               kvm->mmu_invalidate_range_end = end;
> +       } else {
> +               /*
> +                * Fully tracking multiple concurrent ranges has diminishing
> +                * returns. Keep things simple and just find the minimal range
> +                * which includes the current and new ranges. As there won't be
> +                * enough information to subtract a range after its invalidate
> +                * completes, any ranges invalidated concurrently will
> +                * accumulate and persist until all outstanding invalidates
> +                * complete.
> +                */
> +               kvm->mmu_invalidate_range_start =
> +                       min(kvm->mmu_invalidate_range_start, start);
> +               kvm->mmu_invalidate_range_end =
> +                       max(kvm->mmu_invalidate_range_end, end);
> +       }
> +}
> +
> +void kvm_mmu_invalidate_end(struct kvm *kvm)
> +{
> +       /*
> +        * This sequence increase will notify the kvm page fault that
> +        * the page that is going to be mapped in the spte could have
> +        * been freed.
> +        */
> +       kvm->mmu_invalidate_seq++;
> +       smp_wmb();
> +       /*
> +        * The above sequence increase must be visible before the
> +        * below count decrease, which is ensured by the smp_wmb above
> +        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> +        */
> +       kvm->mmu_invalidate_in_progress--;
> +}
> +
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
>  {
> @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
>         kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
>  }
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> -{
> -       /*
> -        * The count increase must become visible at unlock time as no
> -        * spte can be established without taking the mmu_lock and
> -        * count is also read inside the mmu_lock critical section.
> -        */
> -       kvm->mmu_invalidate_in_progress++;
> -
> -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> -               kvm->mmu_invalidate_range_start = INVALID_GPA;
> -               kvm->mmu_invalidate_range_end = INVALID_GPA;
> -       }
> -}
> -
> -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> -       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> -
> -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> -               kvm->mmu_invalidate_range_start = start;
> -               kvm->mmu_invalidate_range_end = end;
> -       } else {
> -               /*
> -                * Fully tracking multiple concurrent ranges has diminishing
> -                * returns. Keep things simple and just find the minimal range
> -                * which includes the current and new ranges. As there won't be
> -                * enough information to subtract a range after its invalidate
> -                * completes, any ranges invalidated concurrently will
> -                * accumulate and persist until all outstanding invalidates
> -                * complete.
> -                */
> -               kvm->mmu_invalidate_range_start =
> -                       min(kvm->mmu_invalidate_range_start, start);
> -               kvm->mmu_invalidate_range_end =
> -                       max(kvm->mmu_invalidate_range_end, end);
> -       }
> -}
> -
>  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>  {
>         kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>         return 0;
>  }
>
> -void kvm_mmu_invalidate_end(struct kvm *kvm)
> -{
> -       /*
> -        * This sequence increase will notify the kvm page fault that
> -        * the page that is going to be mapped in the spte could have
> -        * been freed.
> -        */
> -       kvm->mmu_invalidate_seq++;
> -       smp_wmb();
> -       /*
> -        * The above sequence increase must be visible before the
> -        * below count decrease, which is ensured by the smp_wmb above
> -        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> -        */
> -       kvm->mmu_invalidate_in_progress--;
> -}
> -
>  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
>                                         const struct mmu_notifier_range *range)
>  {
> @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
>         return 0;
>  }
>
> +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> +{
> +       return false;
> +}
> +
>  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>  {
>         struct kvm *kvm = kvm_arch_alloc_vm();
> @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>         return 0;
>  }
>
> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +       struct kvm_gfn_range gfn_range;
> +       struct kvm_memory_slot *slot;
> +       struct kvm_memslots *slots;
> +       struct kvm_memslot_iter iter;
> +       int i;
> +       int r = 0;
> +
> +       gfn_range.pte = __pte(0);
> +       gfn_range.may_block = true;
> +
> +       for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +               slots = __kvm_memslots(kvm, i);
> +
> +               kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> +                       slot = iter.slot;
> +                       gfn_range.start = max(start, slot->base_gfn);
> +                       gfn_range.end = min(end, slot->base_gfn + slot->npages);
> +                       if (gfn_range.start >= gfn_range.end)
> +                               continue;
> +                       gfn_range.slot = slot;
> +
> +                       r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> +               }
> +       }
> +
> +       if (r)
> +               kvm_flush_remote_tlbs(kvm);
> +}
> +
>  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>                                            struct kvm_memory_attributes *attrs)
>  {
>         gfn_t start, end;
>         unsigned long i;
>         void *entry;
> +       int idx;
>         u64 supported_attrs = kvm_supported_mem_attributes(kvm);
>
> -       /* flags is currently not used. */
> +       /* 'flags' is currently not used. */
>         if (attrs->flags)
>                 return -EINVAL;
>         if (attrs->attributes & ~supported_attrs)
> @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>
>         entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
>
> +       if (kvm_arch_has_private_mem(kvm)) {
> +               KVM_MMU_LOCK(kvm);
> +               kvm_mmu_invalidate_begin(kvm);
> +               kvm_mmu_invalidate_range_add(kvm, start, end);
> +               KVM_MMU_UNLOCK(kvm);
> +       }
> +
>         mutex_lock(&kvm->lock);
>         for (i = start; i < end; i++)
>                 if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>                         break;
>         mutex_unlock(&kvm->lock);
>
> +       if (kvm_arch_has_private_mem(kvm)) {
> +               idx = srcu_read_lock(&kvm->srcu);
> +               KVM_MMU_LOCK(kvm);
> +               if (i > start)
> +                       kvm_unmap_mem_range(kvm, start, i);
> +               kvm_mmu_invalidate_end(kvm);
> +               KVM_MMU_UNLOCK(kvm);
> +               srcu_read_unlock(&kvm->srcu, idx);
> +       }
> +
>         attrs->address = i << PAGE_SHIFT;
>         attrs->size = (end - i) << PAGE_SHIFT;
>
> --
> 2.25.1
>

Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

[Yuan Yao]

On Fri, Dec 02, 2022 at 02:13:46PM +0800, Chao Peng wrote:
> A KVM_MEM_PRIVATE memslot can include both fd-based private memory and
> hva-based shared memory. Architecture code (like TDX code) can tell
> whether the on-going fault is private or not. This patch adds a
> 'is_private' field to kvm_page_fault to indicate this and architecture
> code is expected to set it.
>
> To handle page fault for such memslot, the handling logic is different
> depending on whether the fault is private or shared. KVM checks if
> 'is_private' matches the host's view of the page (maintained in
> mem_attr_array).
>   - For a successful match, private pfn is obtained with
>     restrictedmem_get_page() and shared pfn is obtained with existing
>     get_user_pages().
>   - For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
>     userspace. Userspace then can convert memory between private/shared
>     in host's view and retry the fault.
>
> Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++++++++++++++--
>  arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
>  arch/x86/kvm/mmu/mmutrace.h     |  1 +
>  arch/x86/kvm/mmu/tdp_mmu.c      |  2 +-
>  include/linux/kvm_host.h        | 30 ++++++++++++++++
>  5 files changed, 105 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 2190fd8c95c0..b1953ebc012e 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3058,7 +3058,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
>
>  int kvm_mmu_max_mapping_level(struct kvm *kvm,
>  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> -			      int max_level)
> +			      int max_level, bool is_private)
>  {
>  	struct kvm_lpage_info *linfo;
>  	int host_level;
> @@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
>  			break;
>  	}
>
> +	if (is_private)
> +		return max_level;

lpage mixed information already saved, so is that possible
to query info->disallow_lpage without care 'is_private' ?

> +
>  	if (max_level == PG_LEVEL_4K)
>  		return PG_LEVEL_4K;
>
> @@ -3098,7 +3101,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>  	 * level, which will be used to do precise, accurate accounting.
>  	 */
>  	fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> -						     fault->gfn, fault->max_level);
> +						     fault->gfn, fault->max_level,
> +						     fault->is_private);
>  	if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
>  		return;
>
> @@ -4178,6 +4182,49 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>  	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
>  }
>
> +static inline u8 order_to_level(int order)
> +{
> +	BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> +
> +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> +		return PG_LEVEL_1G;
> +
> +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> +		return PG_LEVEL_2M;
> +
> +	return PG_LEVEL_4K;
> +}
> +
> +static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> +				    struct kvm_page_fault *fault)
> +{
> +	vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> +	if (fault->is_private)
> +		vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> +	else
> +		vcpu->run->memory.flags = 0;
> +	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> +	vcpu->run->memory.size = PAGE_SIZE;
> +	return RET_PF_USER;
> +}
> +
> +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> +				   struct kvm_page_fault *fault)
> +{
> +	int order;
> +	struct kvm_memory_slot *slot = fault->slot;
> +
> +	if (!kvm_slot_can_be_private(slot))
> +		return kvm_do_memory_fault_exit(vcpu, fault);
> +
> +	if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> +		return RET_PF_RETRY;
> +
> +	fault->max_level = min(order_to_level(order), fault->max_level);
> +	fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
> +	return RET_PF_CONTINUE;
> +}
> +
>  static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  {
>  	struct kvm_memory_slot *slot = fault->slot;
> @@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  			return RET_PF_EMULATE;
>  	}
>
> +	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> +		return kvm_do_memory_fault_exit(vcpu, fault);
> +
> +	if (fault->is_private)
> +		return kvm_faultin_pfn_private(vcpu, fault);
> +
>  	async = false;
>  	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
>  					  fault->write, &fault->map_writable,
> @@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
>  			return -EIO;
>  	}
>
> +	if (r == RET_PF_USER)
> +		return 0;
> +
>  	if (r < 0)
>  		return r;
>  	if (r != RET_PF_EMULATE)
> @@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>  		 */
>  		if (sp->role.direct &&
>  		    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> -							       PG_LEVEL_NUM)) {
> +							       PG_LEVEL_NUM,
> +							       false)) {
>  			kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
>
>  			if (kvm_available_flush_tlb_with_range())
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index dbaf6755c5a7..5ccf08183b00 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -189,6 +189,7 @@ struct kvm_page_fault {
>
>  	/* Derived from mmu and global state.  */
>  	const bool is_tdp;
> +	const bool is_private;
>  	const bool nx_huge_page_workaround_enabled;
>
>  	/*
> @@ -237,6 +238,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
>   * RET_PF_RETRY: let CPU fault again on the address.
>   * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
>   * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
> + * RET_PF_USER: need to exit to userspace to handle this fault.
>   * RET_PF_FIXED: The faulting entry has been fixed.
>   * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
>   *
> @@ -253,6 +255,7 @@ enum {
>  	RET_PF_RETRY,
>  	RET_PF_EMULATE,
>  	RET_PF_INVALID,
> +	RET_PF_USER,
>  	RET_PF_FIXED,
>  	RET_PF_SPURIOUS,
>  };
> @@ -310,7 +313,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>
>  int kvm_mmu_max_mapping_level(struct kvm *kvm,
>  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> -			      int max_level);
> +			      int max_level, bool is_private);
>  void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
>  void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
>
> @@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
>  void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
>  void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
>
> +#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> +{
> +	WARN_ON_ONCE(1);
> +	return -EOPNOTSUPP;
> +}
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
>  #endif /* __KVM_X86_MMU_INTERNAL_H */
> diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> index ae86820cef69..2d7555381955 100644
> --- a/arch/x86/kvm/mmu/mmutrace.h
> +++ b/arch/x86/kvm/mmu/mmutrace.h
> @@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
>  TRACE_DEFINE_ENUM(RET_PF_RETRY);
>  TRACE_DEFINE_ENUM(RET_PF_EMULATE);
>  TRACE_DEFINE_ENUM(RET_PF_INVALID);
> +TRACE_DEFINE_ENUM(RET_PF_USER);
>  TRACE_DEFINE_ENUM(RET_PF_FIXED);
>  TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 771210ce5181..8ba1a4afc546 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1768,7 +1768,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
>  			continue;
>
>  		max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
> -							      iter.gfn, PG_LEVEL_NUM);
> +						iter.gfn, PG_LEVEL_NUM, false);
>  		if (max_mapping_level < iter.level)
>  			continue;
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 25099c94e770..153842bb33df 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
>  }
>  #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
>
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{
> +	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> +	       KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +}
> +#else
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{
> +	return false;
> +}
> +
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +
> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> +{
> +	int ret;
> +	struct page *page;
> +	pgoff_t index = gfn - slot->base_gfn +
> +			(slot->restricted_offset >> PAGE_SHIFT);
> +
> +	ret = restrictedmem_get_page(slot->restricted_file, index,
> +				     &page, order);
> +	*pfn = page_to_pfn(page);
> +	return ret;
> +}
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
>  #endif
> --
> 2.25.1
>
>

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Xiaoyao Li]

On 12/2/2022 2:13 PM, Chao Peng wrote:

..

> Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> and right now it is selected on X86_64 only.
> 

 From the patch implementation, I have no idea why 
HAVE_KVM_RESTRICTED_MEM is needed.

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Chao Peng]

On Wed, Dec 07, 2022 at 05:16:34PM +0000, Fuad Tabba wrote:
> Hi,
> 
> On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > Unmap the existing guest mappings when memory attribute is changed
> > between shared and private. This is needed because shared pages and
> > private pages are from different backends, unmapping existing ones
> > gives a chance for page fault handler to re-populate the mappings
> > according to the new attribute.
> >
> > Only architecture has private memory support needs this and the
> > supported architecture is expected to rewrite the weak
> > kvm_arch_has_private_mem().
> 
> This kind of ties into the discussion of being able to share memory in
> place. For pKVM for example, shared and private memory would have the
> same backend, and the unmapping wouldn't be needed.
> 
> So I guess that, instead of kvm_arch_has_private_mem(), can the check
> be done differently, e.g., with a different function, say
> kvm_arch_private_notify_attribute_change() (but maybe with a more
> friendly name than what I suggested :) )?

Besides controlling the unmapping here, kvm_arch_has_private_mem() is
also used to gate the memslot KVM_MEM_PRIVATE flag in patch09. I know
unmapping is confirmed unnecessary for pKVM, but how about
KVM_MEM_PRIVATE? Will pKVM add its own flag or reuse KVM_MEM_PRIVATE?
If the answer is the latter, then yes we should use a different check
which only works for confidential usages here.

Thanks,
Chao
> 
> Thanks,
> /fuad
> 
> >
> > Also, during memory attribute changing and the unmapping time frame,
> > page fault handler may happen in the same memory range and can cause
> > incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> > page fault handler retry during this time frame.
> >
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  include/linux/kvm_host.h |   7 +-
> >  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
> >  2 files changed, 116 insertions(+), 59 deletions(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 3d69484d2704..3331c0c92838 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> >  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> >  #endif
> >
> > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> >  struct kvm_gfn_range {
> >         struct kvm_memory_slot *slot;
> >         gfn_t start;
> > @@ -264,6 +263,8 @@ struct kvm_gfn_range {
> >         bool may_block;
> >  };
> >  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> > +
> > +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> >  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> >  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> >  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > @@ -785,11 +786,12 @@ struct kvm {
> >
> >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> >         struct mmu_notifier mmu_notifier;
> > +#endif
> >         unsigned long mmu_invalidate_seq;
> >         long mmu_invalidate_in_progress;
> >         gfn_t mmu_invalidate_range_start;
> >         gfn_t mmu_invalidate_range_end;
> > -#endif
> > +
> >         struct list_head devices;
> >         u64 manual_dirty_log_protect;
> >         struct dentry *debugfs_dentry;
> > @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> >  int kvm_arch_post_init_vm(struct kvm *kvm);
> >  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> >  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> > +bool kvm_arch_has_private_mem(struct kvm *kvm);
> >
> >  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> >  /*
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index ad55dfbc75d7..4e1e1e113bf0 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
> >
> > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > +{
> > +       /*
> > +        * The count increase must become visible at unlock time as no
> > +        * spte can be established without taking the mmu_lock and
> > +        * count is also read inside the mmu_lock critical section.
> > +        */
> > +       kvm->mmu_invalidate_in_progress++;
> > +
> > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > +               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > +               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > +       }
> > +}
> > +
> > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > +{
> > +       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > +
> > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > +               kvm->mmu_invalidate_range_start = start;
> > +               kvm->mmu_invalidate_range_end = end;
> > +       } else {
> > +               /*
> > +                * Fully tracking multiple concurrent ranges has diminishing
> > +                * returns. Keep things simple and just find the minimal range
> > +                * which includes the current and new ranges. As there won't be
> > +                * enough information to subtract a range after its invalidate
> > +                * completes, any ranges invalidated concurrently will
> > +                * accumulate and persist until all outstanding invalidates
> > +                * complete.
> > +                */
> > +               kvm->mmu_invalidate_range_start =
> > +                       min(kvm->mmu_invalidate_range_start, start);
> > +               kvm->mmu_invalidate_range_end =
> > +                       max(kvm->mmu_invalidate_range_end, end);
> > +       }
> > +}
> > +
> > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> > +{
> > +       /*
> > +        * This sequence increase will notify the kvm page fault that
> > +        * the page that is going to be mapped in the spte could have
> > +        * been freed.
> > +        */
> > +       kvm->mmu_invalidate_seq++;
> > +       smp_wmb();
> > +       /*
> > +        * The above sequence increase must be visible before the
> > +        * below count decrease, which is ensured by the smp_wmb above
> > +        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > +        */
> > +       kvm->mmu_invalidate_in_progress--;
> > +}
> > +
> >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> >  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
> >  {
> > @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> >         kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> >  }
> >
> > -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > -{
> > -       /*
> > -        * The count increase must become visible at unlock time as no
> > -        * spte can be established without taking the mmu_lock and
> > -        * count is also read inside the mmu_lock critical section.
> > -        */
> > -       kvm->mmu_invalidate_in_progress++;
> > -
> > -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > -               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > -               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > -       }
> > -}
> > -
> > -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > -{
> > -       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > -
> > -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > -               kvm->mmu_invalidate_range_start = start;
> > -               kvm->mmu_invalidate_range_end = end;
> > -       } else {
> > -               /*
> > -                * Fully tracking multiple concurrent ranges has diminishing
> > -                * returns. Keep things simple and just find the minimal range
> > -                * which includes the current and new ranges. As there won't be
> > -                * enough information to subtract a range after its invalidate
> > -                * completes, any ranges invalidated concurrently will
> > -                * accumulate and persist until all outstanding invalidates
> > -                * complete.
> > -                */
> > -               kvm->mmu_invalidate_range_start =
> > -                       min(kvm->mmu_invalidate_range_start, start);
> > -               kvm->mmu_invalidate_range_end =
> > -                       max(kvm->mmu_invalidate_range_end, end);
> > -       }
> > -}
> > -
> >  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> >  {
> >         kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> >         return 0;
> >  }
> >
> > -void kvm_mmu_invalidate_end(struct kvm *kvm)
> > -{
> > -       /*
> > -        * This sequence increase will notify the kvm page fault that
> > -        * the page that is going to be mapped in the spte could have
> > -        * been freed.
> > -        */
> > -       kvm->mmu_invalidate_seq++;
> > -       smp_wmb();
> > -       /*
> > -        * The above sequence increase must be visible before the
> > -        * below count decrease, which is ensured by the smp_wmb above
> > -        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > -        */
> > -       kvm->mmu_invalidate_in_progress--;
> > -}
> > -
> >  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> >                                         const struct mmu_notifier_range *range)
> >  {
> > @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
> >         return 0;
> >  }
> >
> > +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> > +{
> > +       return false;
> > +}
> > +
> >  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> >  {
> >         struct kvm *kvm = kvm_arch_alloc_vm();
> > @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> >         return 0;
> >  }
> >
> > +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> > +{
> > +       struct kvm_gfn_range gfn_range;
> > +       struct kvm_memory_slot *slot;
> > +       struct kvm_memslots *slots;
> > +       struct kvm_memslot_iter iter;
> > +       int i;
> > +       int r = 0;
> > +
> > +       gfn_range.pte = __pte(0);
> > +       gfn_range.may_block = true;
> > +
> > +       for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > +               slots = __kvm_memslots(kvm, i);
> > +
> > +               kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> > +                       slot = iter.slot;
> > +                       gfn_range.start = max(start, slot->base_gfn);
> > +                       gfn_range.end = min(end, slot->base_gfn + slot->npages);
> > +                       if (gfn_range.start >= gfn_range.end)
> > +                               continue;
> > +                       gfn_range.slot = slot;
> > +
> > +                       r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> > +               }
> > +       }
> > +
> > +       if (r)
> > +               kvm_flush_remote_tlbs(kvm);
> > +}
> > +
> >  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> >                                            struct kvm_memory_attributes *attrs)
> >  {
> >         gfn_t start, end;
> >         unsigned long i;
> >         void *entry;
> > +       int idx;
> >         u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> >
> > -       /* flags is currently not used. */
> > +       /* 'flags' is currently not used. */
> >         if (attrs->flags)
> >                 return -EINVAL;
> >         if (attrs->attributes & ~supported_attrs)
> > @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> >
> >         entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> >
> > +       if (kvm_arch_has_private_mem(kvm)) {
> > +               KVM_MMU_LOCK(kvm);
> > +               kvm_mmu_invalidate_begin(kvm);
> > +               kvm_mmu_invalidate_range_add(kvm, start, end);
> > +               KVM_MMU_UNLOCK(kvm);
> > +       }
> > +
> >         mutex_lock(&kvm->lock);
> >         for (i = start; i < end; i++)
> >                 if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> >                         break;
> >         mutex_unlock(&kvm->lock);
> >
> > +       if (kvm_arch_has_private_mem(kvm)) {
> > +               idx = srcu_read_lock(&kvm->srcu);
> > +               KVM_MMU_LOCK(kvm);
> > +               if (i > start)
> > +                       kvm_unmap_mem_range(kvm, start, i);
> > +               kvm_mmu_invalidate_end(kvm);
> > +               KVM_MMU_UNLOCK(kvm);
> > +               srcu_read_unlock(&kvm->srcu, idx);
> > +       }
> > +
> >         attrs->address = i << PAGE_SHIFT;
> >         attrs->size = (end - i) << PAGE_SHIFT;
> >
> > --
> > 2.25.1
> >

Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Chao Peng]

On Tue, Dec 06, 2022 at 10:42:24PM -0800, Isaku Yamahata wrote:
> On Tue, Dec 06, 2022 at 08:02:24PM +0800,
> Chao Peng <chao.p.peng@linux.intel.com> wrote:
> 
> > On Mon, Dec 05, 2022 at 02:49:59PM -0800, Isaku Yamahata wrote:
> > > On Fri, Dec 02, 2022 at 02:13:45PM +0800,
> > > Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > > 
> > > > A large page with mixed private/shared subpages can't be mapped as large
> > > > page since its sub private/shared pages are from different memory
> > > > backends and may also treated by architecture differently. When
> > > > private/shared memory are mixed in a large page, the current lpage_info
> > > > is not sufficient to decide whether the page can be mapped as large page
> > > > or not and additional private/shared mixed information is needed.
> > > > 
> > > > Tracking this 'mixed' information with the current 'count' like
> > > > disallow_lpage is a bit challenge so reserve a bit in 'disallow_lpage'
> > > > to indicate a large page has mixed private/share subpages and update
> > > > this 'mixed' bit whenever the memory attribute is changed between
> > > > private and shared.
> > > > 
> > > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > > ---
> > > >  arch/x86/include/asm/kvm_host.h |   8 ++
> > > >  arch/x86/kvm/mmu/mmu.c          | 134 +++++++++++++++++++++++++++++++-
> > > >  arch/x86/kvm/x86.c              |   2 +
> > > >  include/linux/kvm_host.h        |  19 +++++
> > > >  virt/kvm/kvm_main.c             |   9 ++-
> > > >  5 files changed, 169 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > > > index 283cbb83d6ae..7772ab37ac89 100644
> > > > --- a/arch/x86/include/asm/kvm_host.h
> > > > +++ b/arch/x86/include/asm/kvm_host.h
> > > > @@ -38,6 +38,7 @@
> > > >  #include <asm/hyperv-tlfs.h>
> > > >  
> > > >  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
> > > > +#define __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
> > > >  
> > > >  #define KVM_MAX_VCPUS 1024
> > > >  
> > > > @@ -1011,6 +1012,13 @@ struct kvm_vcpu_arch {
> > > >  #endif
> > > >  };
> > > >  
> > > > +/*
> > > > + * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
> > > > + * level. The remaining bits are used as a reference count.
> > > > + */
> > > > +#define KVM_LPAGE_PRIVATE_SHARED_MIXED		(1U << 31)
> > > > +#define KVM_LPAGE_COUNT_MAX			((1U << 31) - 1)
> > > > +
> > > >  struct kvm_lpage_info {
> > > >  	int disallow_lpage;
> > > >  };
> > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > > index e2c70b5afa3e..2190fd8c95c0 100644
> > > > --- a/arch/x86/kvm/mmu/mmu.c
> > > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > > @@ -763,11 +763,16 @@ static void update_gfn_disallow_lpage_count(const struct kvm_memory_slot *slot,
> > > >  {
> > > >  	struct kvm_lpage_info *linfo;
> > > >  	int i;
> > > > +	int disallow_count;
> > > >  
> > > >  	for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
> > > >  		linfo = lpage_info_slot(gfn, slot, i);
> > > > +
> > > > +		disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
> > > > +		WARN_ON(disallow_count + count < 0 ||
> > > > +			disallow_count > KVM_LPAGE_COUNT_MAX - count);
> > > > +
> > > >  		linfo->disallow_lpage += count;
> > > > -		WARN_ON(linfo->disallow_lpage < 0);
> > > >  	}
> > > >  }
> > > >  
> > > > @@ -6986,3 +6991,130 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
> > > >  	if (kvm->arch.nx_huge_page_recovery_thread)
> > > >  		kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
> > > >  }
> > > > +
> > > > +static bool linfo_is_mixed(struct kvm_lpage_info *linfo)
> > > > +{
> > > > +	return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > > > +}
> > > > +
> > > > +static void linfo_set_mixed(gfn_t gfn, struct kvm_memory_slot *slot,
> > > > +			    int level, bool mixed)
> > > > +{
> > > > +	struct kvm_lpage_info *linfo = lpage_info_slot(gfn, slot, level);
> > > > +
> > > > +	if (mixed)
> > > > +		linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > > > +	else
> > > > +		linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > > > +}
> > > > +
> > > > +static bool is_expected_attr_entry(void *entry, unsigned long expected_attrs)
> > > > +{
> > > > +	bool expect_private = expected_attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > > > +
> > > > +	if (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) {
> > > > +		if (!expect_private)
> > > > +			return false;
> > > > +	} else if (expect_private)
> > > > +		return false;
> > > > +
> > > > +	return true;
> > > > +}
> > > > +
> > > > +static bool mem_attrs_mixed_2m(struct kvm *kvm, unsigned long attrs,
> > > > +			       gfn_t start, gfn_t end)
> > > > +{
> > > > +	XA_STATE(xas, &kvm->mem_attr_array, start);
> > > > +	gfn_t gfn = start;
> > > > +	void *entry;
> > > > +	bool mixed = false;
> > > > +
> > > > +	rcu_read_lock();
> > > > +	entry = xas_load(&xas);
> > > > +	while (gfn < end) {
> > > > +		if (xas_retry(&xas, entry))
> > > > +			continue;
> > > > +
> > > > +		KVM_BUG_ON(gfn != xas.xa_index, kvm);
> > > > +
> > > > +		if (!is_expected_attr_entry(entry, attrs)) {
> > > > +			mixed = true;
> > > > +			break;
> > > > +		}
> > > > +
> > > > +		entry = xas_next(&xas);
> > > > +		gfn++;
> > > > +	}
> > > > +
> > > > +	rcu_read_unlock();
> > > > +	return mixed;
> > > > +}
> > > > +
> > > > +static bool mem_attrs_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
> > > > +			    int level, unsigned long attrs,
> > > > +			    gfn_t start, gfn_t end)
> > > > +{
> > > > +	unsigned long gfn;
> > > > +
> > > > +	if (level == PG_LEVEL_2M)
> > > > +		return mem_attrs_mixed_2m(kvm, attrs, start, end);
> > > > +
> > > > +	for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1))
> > > > +		if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
> > > > +		    !is_expected_attr_entry(xa_load(&kvm->mem_attr_array, gfn),
> > > > +					    attrs))
> > > > +			return true;
> > > > +	return false;
> > > > +}
> > > > +
> > > > +static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
> > > > +						  struct kvm_memory_slot *slot,
> > > > +						  unsigned long attrs,
> > > > +						  gfn_t start, gfn_t end)
> > > > +{
> > > > +	unsigned long pages, mask;
> > > > +	gfn_t gfn, gfn_end, first, last;
> > > > +	int level;
> > > > +	bool mixed;
> > > > +
> > > > +	/*
> > > > +	 * The sequence matters here: we set the higher level basing on the
> > > > +	 * lower level's scanning result.
> > > > +	 */
> > > > +	for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> > > > +		pages = KVM_PAGES_PER_HPAGE(level);
> > > > +		mask = ~(pages - 1);
> > > > +		first = start & mask;
> > > > +		last = (end - 1) & mask;
> > > > +
> > > > +		/*
> > > > +		 * We only need to scan the head and tail page, for middle pages
> > > > +		 * we know they will not be mixed.
> > > > +		 */
> > > > +		gfn = max(first, slot->base_gfn);
> > > > +		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
> > > > +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> > > > +		linfo_set_mixed(gfn, slot, level, mixed);
> > > > +
> > > > +		if (first == last)
> > > > +			return;
> > > 
> > > 
> > > continue.
> > 
> > Ya!
> > 
> > > 
> > > > +
> > > > +		for (gfn = first + pages; gfn < last; gfn += pages)
> > > > +			linfo_set_mixed(gfn, slot, level, false);
> > > > +
> > > > +		gfn = last;
> > > > +		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
> > > 
> > > if (gfn == gfn_end) continue.
> > 
> > Do you see a case where gfn can equal to gfn_end? Though it does not
> > hurt to add a check.
> 
> If last == base_gfn + npages, gfn == gfn_end can occur.

'end' is guaranteed <=  base_gfn + npages in kvm_unmap_mem_range():
	gfn_range.end = min(end, slot->base_gfn + slot->npages);

And 'last' is defined as:
	last = (end - 1) & mask;

Then the math is:
	last = (end - 1) & mask
	     <= end - 1
	     <= base_gfn + npages - 1
	     <  base_gfn + npages

Thanks,
Chao
> 
> 
> > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > > index 9a07380f8d3c..5aefcff614d2 100644
> > > > --- a/arch/x86/kvm/x86.c
> > > > +++ b/arch/x86/kvm/x86.c
> > > > @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
> > > >  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
> > > >  			linfo[lpages - 1].disallow_lpage = 1;
> > > >  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> > > > +		if (kvm_slot_can_be_private(slot))
> > > > +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
> > > 
> > > Is there any alignment restriction? If no, It should be +=.
> > > In practice, alignment will hold though.
> > 
> > All we need here is checking whether both userspace_addr and
> > restricted_offset are aligned to HPAGE_SIZE or not. '+=' actually can
> > yield wrong value in cases when userspace_addr + restricted_offset is
> > aligned to HPAGE_SIZE but individually they may not align to HPAGE_SIZE.
> 
> Ah, got it. The blow comment explains it.
> 
> > Thanks,
> > Chao
> > > 
> > > Thanks,
> > > 
> > > >  		/*
> > > >  		 * If the gfn and userspace address are not aligned wrt each
> > > >  		 * other, disable large page support for this slot.
> -- 
> Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Chao Peng]

On Wed, Dec 07, 2022 at 04:13:14PM +0800, Yuan Yao wrote:
> On Fri, Dec 02, 2022 at 02:13:44PM +0800, Chao Peng wrote:
> > Unmap the existing guest mappings when memory attribute is changed
> > between shared and private. This is needed because shared pages and
> > private pages are from different backends, unmapping existing ones
> > gives a chance for page fault handler to re-populate the mappings
> > according to the new attribute.
> >
> > Only architecture has private memory support needs this and the
> > supported architecture is expected to rewrite the weak
> > kvm_arch_has_private_mem().
> >
> > Also, during memory attribute changing and the unmapping time frame,
> > page fault handler may happen in the same memory range and can cause
> > incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> > page fault handler retry during this time frame.
> >
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  include/linux/kvm_host.h |   7 +-
> >  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
> >  2 files changed, 116 insertions(+), 59 deletions(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 3d69484d2704..3331c0c92838 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> >  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> >  #endif
> >
> > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> >  struct kvm_gfn_range {
> >  	struct kvm_memory_slot *slot;
> >  	gfn_t start;
> > @@ -264,6 +263,8 @@ struct kvm_gfn_range {
> >  	bool may_block;
> >  };
> >  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> > +
> > +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> >  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> >  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> >  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > @@ -785,11 +786,12 @@ struct kvm {
> >
> >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> >  	struct mmu_notifier mmu_notifier;
> > +#endif
> >  	unsigned long mmu_invalidate_seq;
> >  	long mmu_invalidate_in_progress;
> >  	gfn_t mmu_invalidate_range_start;
> >  	gfn_t mmu_invalidate_range_end;
> > -#endif
> > +
> >  	struct list_head devices;
> >  	u64 manual_dirty_log_protect;
> >  	struct dentry *debugfs_dentry;
> > @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> >  int kvm_arch_post_init_vm(struct kvm *kvm);
> >  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> >  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> > +bool kvm_arch_has_private_mem(struct kvm *kvm);
> >
> >  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> >  /*
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index ad55dfbc75d7..4e1e1e113bf0 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
> >
> > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > +{
> > +	/*
> > +	 * The count increase must become visible at unlock time as no
> > +	 * spte can be established without taking the mmu_lock and
> > +	 * count is also read inside the mmu_lock critical section.
> > +	 */
> > +	kvm->mmu_invalidate_in_progress++;
> > +
> > +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > +		kvm->mmu_invalidate_range_start = INVALID_GPA;
> > +		kvm->mmu_invalidate_range_end = INVALID_GPA;
> > +	}
> > +}
> > +
> > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > +{
> > +	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > +
> > +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > +		kvm->mmu_invalidate_range_start = start;
> > +		kvm->mmu_invalidate_range_end = end;
> > +	} else {
> > +		/*
> > +		 * Fully tracking multiple concurrent ranges has diminishing
> > +		 * returns. Keep things simple and just find the minimal range
> > +		 * which includes the current and new ranges. As there won't be
> > +		 * enough information to subtract a range after its invalidate
> > +		 * completes, any ranges invalidated concurrently will
> > +		 * accumulate and persist until all outstanding invalidates
> > +		 * complete.
> > +		 */
> > +		kvm->mmu_invalidate_range_start =
> > +			min(kvm->mmu_invalidate_range_start, start);
> > +		kvm->mmu_invalidate_range_end =
> > +			max(kvm->mmu_invalidate_range_end, end);
> > +	}
> > +}
> > +
> > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> > +{
> > +	/*
> > +	 * This sequence increase will notify the kvm page fault that
> > +	 * the page that is going to be mapped in the spte could have
> > +	 * been freed.
> > +	 */
> > +	kvm->mmu_invalidate_seq++;
> > +	smp_wmb();
> > +	/*
> > +	 * The above sequence increase must be visible before the
> > +	 * below count decrease, which is ensured by the smp_wmb above
> > +	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > +	 */
> > +	kvm->mmu_invalidate_in_progress--;
> > +}
> > +
> >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> >  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
> >  {
> > @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> >  	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> >  }
> >
> > -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > -{
> > -	/*
> > -	 * The count increase must become visible at unlock time as no
> > -	 * spte can be established without taking the mmu_lock and
> > -	 * count is also read inside the mmu_lock critical section.
> > -	 */
> > -	kvm->mmu_invalidate_in_progress++;
> > -
> > -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > -		kvm->mmu_invalidate_range_start = INVALID_GPA;
> > -		kvm->mmu_invalidate_range_end = INVALID_GPA;
> > -	}
> > -}
> > -
> > -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > -{
> > -	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > -
> > -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > -		kvm->mmu_invalidate_range_start = start;
> > -		kvm->mmu_invalidate_range_end = end;
> > -	} else {
> > -		/*
> > -		 * Fully tracking multiple concurrent ranges has diminishing
> > -		 * returns. Keep things simple and just find the minimal range
> > -		 * which includes the current and new ranges. As there won't be
> > -		 * enough information to subtract a range after its invalidate
> > -		 * completes, any ranges invalidated concurrently will
> > -		 * accumulate and persist until all outstanding invalidates
> > -		 * complete.
> > -		 */
> > -		kvm->mmu_invalidate_range_start =
> > -			min(kvm->mmu_invalidate_range_start, start);
> > -		kvm->mmu_invalidate_range_end =
> > -			max(kvm->mmu_invalidate_range_end, end);
> > -	}
> > -}
> > -
> >  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> >  {
> >  	kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> >  	return 0;
> >  }
> >
> > -void kvm_mmu_invalidate_end(struct kvm *kvm)
> > -{
> > -	/*
> > -	 * This sequence increase will notify the kvm page fault that
> > -	 * the page that is going to be mapped in the spte could have
> > -	 * been freed.
> > -	 */
> > -	kvm->mmu_invalidate_seq++;
> > -	smp_wmb();
> > -	/*
> > -	 * The above sequence increase must be visible before the
> > -	 * below count decrease, which is ensured by the smp_wmb above
> > -	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > -	 */
> > -	kvm->mmu_invalidate_in_progress--;
> > -}
> > -
> >  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> >  					const struct mmu_notifier_range *range)
> >  {
> > @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
> >  	return 0;
> >  }
> >
> > +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> > +{
> > +	return false;
> > +}
> > +
> >  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> >  {
> >  	struct kvm *kvm = kvm_arch_alloc_vm();
> > @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> >  	return 0;
> >  }
> >
> > +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> > +{
> > +	struct kvm_gfn_range gfn_range;
> > +	struct kvm_memory_slot *slot;
> > +	struct kvm_memslots *slots;
> > +	struct kvm_memslot_iter iter;
> > +	int i;
> > +	int r = 0;
> > +
> > +	gfn_range.pte = __pte(0);
> > +	gfn_range.may_block = true;
> > +
> > +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > +		slots = __kvm_memslots(kvm, i);
> > +
> > +		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> > +			slot = iter.slot;
> > +			gfn_range.start = max(start, slot->base_gfn);
> > +			gfn_range.end = min(end, slot->base_gfn + slot->npages);
> > +			if (gfn_range.start >= gfn_range.end)
> > +				continue;
> > +			gfn_range.slot = slot;
> > +
> > +			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> > +		}
> > +	}
> > +
> > +	if (r)
> > +		kvm_flush_remote_tlbs(kvm);
> > +}
> > +
> >  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> >  					   struct kvm_memory_attributes *attrs)
> >  {
> >  	gfn_t start, end;
> >  	unsigned long i;
> >  	void *entry;
> > +	int idx;
> >  	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> >
> > -	/* flags is currently not used. */
> > +	/* 'flags' is currently not used. */
> >  	if (attrs->flags)
> >  		return -EINVAL;
> >  	if (attrs->attributes & ~supported_attrs)
> > @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> >
> >  	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> >
> > +	if (kvm_arch_has_private_mem(kvm)) {
> > +		KVM_MMU_LOCK(kvm);
> > +		kvm_mmu_invalidate_begin(kvm);
> > +		kvm_mmu_invalidate_range_add(kvm, start, end);
> 
> Nit: this works for KVM_MEMORY_ATTRIBUTE_PRIVATE, but
> the invalidation should be necessary yet for attribute change of:
> 
> KVM_MEMORY_ATTRIBUTE_READ
> KVM_MEMORY_ATTRIBUTE_WRITE
> KVM_MEMORY_ATTRIBUTE_EXECUTE

The unmapping is only needed for confidential usages which uses
KVM_MEMORY_ATTRIBUTE_PRIVATE only and the other flags are defined here
for other usages like pKVM. As Fuad commented in a different reply, pKVM
supports in-place remapping and unmapping is unnecessary.

Thanks,
Chao
> 
> > +		KVM_MMU_UNLOCK(kvm);
> > +	}
> > +
> >  	mutex_lock(&kvm->lock);
> >  	for (i = start; i < end; i++)
> >  		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> >  			break;
> >  	mutex_unlock(&kvm->lock);
> >
> > +	if (kvm_arch_has_private_mem(kvm)) {
> > +		idx = srcu_read_lock(&kvm->srcu);
> > +		KVM_MMU_LOCK(kvm);
> > +		if (i > start)
> > +			kvm_unmap_mem_range(kvm, start, i);
> > +		kvm_mmu_invalidate_end(kvm);
> 
> Ditto.
> 
> > +		KVM_MMU_UNLOCK(kvm);
> > +		srcu_read_unlock(&kvm->srcu, idx);
> > +	}
> > +
> >  	attrs->address = i << PAGE_SHIFT;
> >  	attrs->size = (end - i) << PAGE_SHIFT;
> >
> > --
> > 2.25.1
> >
> >

Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

[Chao Peng]

On Thu, Dec 08, 2022 at 10:29:18AM +0800, Yuan Yao wrote:
> On Fri, Dec 02, 2022 at 02:13:46PM +0800, Chao Peng wrote:
> > A KVM_MEM_PRIVATE memslot can include both fd-based private memory and
> > hva-based shared memory. Architecture code (like TDX code) can tell
> > whether the on-going fault is private or not. This patch adds a
> > 'is_private' field to kvm_page_fault to indicate this and architecture
> > code is expected to set it.
> >
> > To handle page fault for such memslot, the handling logic is different
> > depending on whether the fault is private or shared. KVM checks if
> > 'is_private' matches the host's view of the page (maintained in
> > mem_attr_array).
> >   - For a successful match, private pfn is obtained with
> >     restrictedmem_get_page() and shared pfn is obtained with existing
> >     get_user_pages().
> >   - For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
> >     userspace. Userspace then can convert memory between private/shared
> >     in host's view and retry the fault.
> >
> > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++++++++++++++--
> >  arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
> >  arch/x86/kvm/mmu/mmutrace.h     |  1 +
> >  arch/x86/kvm/mmu/tdp_mmu.c      |  2 +-
> >  include/linux/kvm_host.h        | 30 ++++++++++++++++
> >  5 files changed, 105 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 2190fd8c95c0..b1953ebc012e 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3058,7 +3058,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
> >
> >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> >  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> > -			      int max_level)
> > +			      int max_level, bool is_private)
> >  {
> >  	struct kvm_lpage_info *linfo;
> >  	int host_level;
> > @@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> >  			break;
> >  	}
> >
> > +	if (is_private)
> > +		return max_level;
> 
> lpage mixed information already saved, so is that possible
> to query info->disallow_lpage without care 'is_private' ?

Actually we already queried info->disallow_lpage just before this
sentence. The check is needed because later in the function we call
host_pfn_mapping_level() which is shared memory specific.

Thanks,
Chao
> 
> > +
> >  	if (max_level == PG_LEVEL_4K)
> >  		return PG_LEVEL_4K;
> >
> > @@ -3098,7 +3101,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> >  	 * level, which will be used to do precise, accurate accounting.
> >  	 */
> >  	fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> > -						     fault->gfn, fault->max_level);
> > +						     fault->gfn, fault->max_level,
> > +						     fault->is_private);
> >  	if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
> >  		return;
> >
> > @@ -4178,6 +4182,49 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> >  	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
> >  }
> >
> > +static inline u8 order_to_level(int order)
> > +{
> > +	BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> > +
> > +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> > +		return PG_LEVEL_1G;
> > +
> > +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> > +		return PG_LEVEL_2M;
> > +
> > +	return PG_LEVEL_4K;
> > +}
> > +
> > +static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> > +				    struct kvm_page_fault *fault)
> > +{
> > +	vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> > +	if (fault->is_private)
> > +		vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> > +	else
> > +		vcpu->run->memory.flags = 0;
> > +	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> > +	vcpu->run->memory.size = PAGE_SIZE;
> > +	return RET_PF_USER;
> > +}
> > +
> > +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> > +				   struct kvm_page_fault *fault)
> > +{
> > +	int order;
> > +	struct kvm_memory_slot *slot = fault->slot;
> > +
> > +	if (!kvm_slot_can_be_private(slot))
> > +		return kvm_do_memory_fault_exit(vcpu, fault);
> > +
> > +	if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> > +		return RET_PF_RETRY;
> > +
> > +	fault->max_level = min(order_to_level(order), fault->max_level);
> > +	fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
> > +	return RET_PF_CONTINUE;
> > +}
> > +
> >  static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >  {
> >  	struct kvm_memory_slot *slot = fault->slot;
> > @@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >  			return RET_PF_EMULATE;
> >  	}
> >
> > +	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> > +		return kvm_do_memory_fault_exit(vcpu, fault);
> > +
> > +	if (fault->is_private)
> > +		return kvm_faultin_pfn_private(vcpu, fault);
> > +
> >  	async = false;
> >  	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
> >  					  fault->write, &fault->map_writable,
> > @@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
> >  			return -EIO;
> >  	}
> >
> > +	if (r == RET_PF_USER)
> > +		return 0;
> > +
> >  	if (r < 0)
> >  		return r;
> >  	if (r != RET_PF_EMULATE)
> > @@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> >  		 */
> >  		if (sp->role.direct &&
> >  		    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> > -							       PG_LEVEL_NUM)) {
> > +							       PG_LEVEL_NUM,
> > +							       false)) {
> >  			kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
> >
> >  			if (kvm_available_flush_tlb_with_range())
> > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> > index dbaf6755c5a7..5ccf08183b00 100644
> > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > @@ -189,6 +189,7 @@ struct kvm_page_fault {
> >
> >  	/* Derived from mmu and global state.  */
> >  	const bool is_tdp;
> > +	const bool is_private;
> >  	const bool nx_huge_page_workaround_enabled;
> >
> >  	/*
> > @@ -237,6 +238,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> >   * RET_PF_RETRY: let CPU fault again on the address.
> >   * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
> >   * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
> > + * RET_PF_USER: need to exit to userspace to handle this fault.
> >   * RET_PF_FIXED: The faulting entry has been fixed.
> >   * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
> >   *
> > @@ -253,6 +255,7 @@ enum {
> >  	RET_PF_RETRY,
> >  	RET_PF_EMULATE,
> >  	RET_PF_INVALID,
> > +	RET_PF_USER,
> >  	RET_PF_FIXED,
> >  	RET_PF_SPURIOUS,
> >  };
> > @@ -310,7 +313,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> >
> >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> >  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> > -			      int max_level);
> > +			      int max_level, bool is_private);
> >  void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> >  void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
> >
> > @@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> >  void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> >  void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> >
> > +#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > +{
> > +	WARN_ON_ONCE(1);
> > +	return -EOPNOTSUPP;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > +
> >  #endif /* __KVM_X86_MMU_INTERNAL_H */
> > diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> > index ae86820cef69..2d7555381955 100644
> > --- a/arch/x86/kvm/mmu/mmutrace.h
> > +++ b/arch/x86/kvm/mmu/mmutrace.h
> > @@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
> >  TRACE_DEFINE_ENUM(RET_PF_RETRY);
> >  TRACE_DEFINE_ENUM(RET_PF_EMULATE);
> >  TRACE_DEFINE_ENUM(RET_PF_INVALID);
> > +TRACE_DEFINE_ENUM(RET_PF_USER);
> >  TRACE_DEFINE_ENUM(RET_PF_FIXED);
> >  TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
> >
> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index 771210ce5181..8ba1a4afc546 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -1768,7 +1768,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
> >  			continue;
> >
> >  		max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
> > -							      iter.gfn, PG_LEVEL_NUM);
> > +						iter.gfn, PG_LEVEL_NUM, false);
> >  		if (max_mapping_level < iter.level)
> >  			continue;
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 25099c94e770..153842bb33df 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> >  }
> >  #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
> >
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > +{
> > +	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> > +	       KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > +}
> > +#else
> > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > +{
> > +	return false;
> > +}
> > +
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > +
> > +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > +{
> > +	int ret;
> > +	struct page *page;
> > +	pgoff_t index = gfn - slot->base_gfn +
> > +			(slot->restricted_offset >> PAGE_SHIFT);
> > +
> > +	ret = restrictedmem_get_page(slot->restricted_file, index,
> > +				     &page, order);
> > +	*pfn = page_to_pfn(page);
> > +	return ret;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > +
> >  #endif
> > --
> > 2.25.1
> >
> >

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Thu, Dec 08, 2022 at 04:37:03PM +0800, Xiaoyao Li wrote:
> On 12/2/2022 2:13 PM, Chao Peng wrote:
> 
> ..
> 
> > Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> > and right now it is selected on X86_64 only.
> > 
> 
> From the patch implementation, I have no idea why HAVE_KVM_RESTRICTED_MEM is
> needed.

The reason is we want KVM further controls the feature enabling. An
opt-in CONFIG_RESTRICTEDMEM can cause problem if user sets that for
unsupported architectures.

Here is the original discussion:
https://lore.kernel.org/all/YkJLFu98hZOvTSrL@google.com/

Thanks,
Chao

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Yuan Yao]

On Thu, Dec 08, 2022 at 07:20:43PM +0800, Chao Peng wrote:
> On Wed, Dec 07, 2022 at 04:13:14PM +0800, Yuan Yao wrote:
> > On Fri, Dec 02, 2022 at 02:13:44PM +0800, Chao Peng wrote:
> > > Unmap the existing guest mappings when memory attribute is changed
> > > between shared and private. This is needed because shared pages and
> > > private pages are from different backends, unmapping existing ones
> > > gives a chance for page fault handler to re-populate the mappings
> > > according to the new attribute.
> > >
> > > Only architecture has private memory support needs this and the
> > > supported architecture is expected to rewrite the weak
> > > kvm_arch_has_private_mem().
> > >
> > > Also, during memory attribute changing and the unmapping time frame,
> > > page fault handler may happen in the same memory range and can cause
> > > incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> > > page fault handler retry during this time frame.
> > >
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > ---
> > >  include/linux/kvm_host.h |   7 +-
> > >  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
> > >  2 files changed, 116 insertions(+), 59 deletions(-)
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 3d69484d2704..3331c0c92838 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > >  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> > >  #endif
> > >
> > > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > >  struct kvm_gfn_range {
> > >  	struct kvm_memory_slot *slot;
> > >  	gfn_t start;
> > > @@ -264,6 +263,8 @@ struct kvm_gfn_range {
> > >  	bool may_block;
> > >  };
> > >  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> > > +
> > > +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > >  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > >  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > >  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > > @@ -785,11 +786,12 @@ struct kvm {
> > >
> > >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> > >  	struct mmu_notifier mmu_notifier;
> > > +#endif
> > >  	unsigned long mmu_invalidate_seq;
> > >  	long mmu_invalidate_in_progress;
> > >  	gfn_t mmu_invalidate_range_start;
> > >  	gfn_t mmu_invalidate_range_end;
> > > -#endif
> > > +
> > >  	struct list_head devices;
> > >  	u64 manual_dirty_log_protect;
> > >  	struct dentry *debugfs_dentry;
> > > @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> > >  int kvm_arch_post_init_vm(struct kvm *kvm);
> > >  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> > >  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> > > +bool kvm_arch_has_private_mem(struct kvm *kvm);
> > >
> > >  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> > >  /*
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index ad55dfbc75d7..4e1e1e113bf0 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
> > >  }
> > >  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
> > >
> > > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > +{
> > > +	/*
> > > +	 * The count increase must become visible at unlock time as no
> > > +	 * spte can be established without taking the mmu_lock and
> > > +	 * count is also read inside the mmu_lock critical section.
> > > +	 */
> > > +	kvm->mmu_invalidate_in_progress++;
> > > +
> > > +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > +		kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > +		kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > +	}
> > > +}
> > > +
> > > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > > +{
> > > +	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > +
> > > +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > +		kvm->mmu_invalidate_range_start = start;
> > > +		kvm->mmu_invalidate_range_end = end;
> > > +	} else {
> > > +		/*
> > > +		 * Fully tracking multiple concurrent ranges has diminishing
> > > +		 * returns. Keep things simple and just find the minimal range
> > > +		 * which includes the current and new ranges. As there won't be
> > > +		 * enough information to subtract a range after its invalidate
> > > +		 * completes, any ranges invalidated concurrently will
> > > +		 * accumulate and persist until all outstanding invalidates
> > > +		 * complete.
> > > +		 */
> > > +		kvm->mmu_invalidate_range_start =
> > > +			min(kvm->mmu_invalidate_range_start, start);
> > > +		kvm->mmu_invalidate_range_end =
> > > +			max(kvm->mmu_invalidate_range_end, end);
> > > +	}
> > > +}
> > > +
> > > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > +{
> > > +	/*
> > > +	 * This sequence increase will notify the kvm page fault that
> > > +	 * the page that is going to be mapped in the spte could have
> > > +	 * been freed.
> > > +	 */
> > > +	kvm->mmu_invalidate_seq++;
> > > +	smp_wmb();
> > > +	/*
> > > +	 * The above sequence increase must be visible before the
> > > +	 * below count decrease, which is ensured by the smp_wmb above
> > > +	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > > +	 */
> > > +	kvm->mmu_invalidate_in_progress--;
> > > +}
> > > +
> > >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> > >  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
> > >  {
> > > @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> > >  	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> > >  }
> > >
> > > -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > -{
> > > -	/*
> > > -	 * The count increase must become visible at unlock time as no
> > > -	 * spte can be established without taking the mmu_lock and
> > > -	 * count is also read inside the mmu_lock critical section.
> > > -	 */
> > > -	kvm->mmu_invalidate_in_progress++;
> > > -
> > > -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > -		kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > -		kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > -	}
> > > -}
> > > -
> > > -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > > -{
> > > -	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > -
> > > -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > -		kvm->mmu_invalidate_range_start = start;
> > > -		kvm->mmu_invalidate_range_end = end;
> > > -	} else {
> > > -		/*
> > > -		 * Fully tracking multiple concurrent ranges has diminishing
> > > -		 * returns. Keep things simple and just find the minimal range
> > > -		 * which includes the current and new ranges. As there won't be
> > > -		 * enough information to subtract a range after its invalidate
> > > -		 * completes, any ranges invalidated concurrently will
> > > -		 * accumulate and persist until all outstanding invalidates
> > > -		 * complete.
> > > -		 */
> > > -		kvm->mmu_invalidate_range_start =
> > > -			min(kvm->mmu_invalidate_range_start, start);
> > > -		kvm->mmu_invalidate_range_end =
> > > -			max(kvm->mmu_invalidate_range_end, end);
> > > -	}
> > > -}
> > > -
> > >  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> > >  {
> > >  	kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > > @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> > >  	return 0;
> > >  }
> > >
> > > -void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > -{
> > > -	/*
> > > -	 * This sequence increase will notify the kvm page fault that
> > > -	 * the page that is going to be mapped in the spte could have
> > > -	 * been freed.
> > > -	 */
> > > -	kvm->mmu_invalidate_seq++;
> > > -	smp_wmb();
> > > -	/*
> > > -	 * The above sequence increase must be visible before the
> > > -	 * below count decrease, which is ensured by the smp_wmb above
> > > -	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > > -	 */
> > > -	kvm->mmu_invalidate_in_progress--;
> > > -}
> > > -
> > >  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> > >  					const struct mmu_notifier_range *range)
> > >  {
> > > @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
> > >  	return 0;
> > >  }
> > >
> > > +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> > > +{
> > > +	return false;
> > > +}
> > > +
> > >  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> > >  {
> > >  	struct kvm *kvm = kvm_arch_alloc_vm();
> > > @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> > >  	return 0;
> > >  }
> > >
> > > +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> > > +{
> > > +	struct kvm_gfn_range gfn_range;
> > > +	struct kvm_memory_slot *slot;
> > > +	struct kvm_memslots *slots;
> > > +	struct kvm_memslot_iter iter;
> > > +	int i;
> > > +	int r = 0;
> > > +
> > > +	gfn_range.pte = __pte(0);
> > > +	gfn_range.may_block = true;
> > > +
> > > +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > > +		slots = __kvm_memslots(kvm, i);
> > > +
> > > +		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> > > +			slot = iter.slot;
> > > +			gfn_range.start = max(start, slot->base_gfn);
> > > +			gfn_range.end = min(end, slot->base_gfn + slot->npages);
> > > +			if (gfn_range.start >= gfn_range.end)
> > > +				continue;
> > > +			gfn_range.slot = slot;
> > > +
> > > +			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> > > +		}
> > > +	}
> > > +
> > > +	if (r)
> > > +		kvm_flush_remote_tlbs(kvm);
> > > +}
> > > +
> > >  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > >  					   struct kvm_memory_attributes *attrs)
> > >  {
> > >  	gfn_t start, end;
> > >  	unsigned long i;
> > >  	void *entry;
> > > +	int idx;
> > >  	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > >
> > > -	/* flags is currently not used. */
> > > +	/* 'flags' is currently not used. */
> > >  	if (attrs->flags)
> > >  		return -EINVAL;
> > >  	if (attrs->attributes & ~supported_attrs)
> > > @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > >
> > >  	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > >
> > > +	if (kvm_arch_has_private_mem(kvm)) {
> > > +		KVM_MMU_LOCK(kvm);
> > > +		kvm_mmu_invalidate_begin(kvm);
> > > +		kvm_mmu_invalidate_range_add(kvm, start, end);
> >
> > Nit: this works for KVM_MEMORY_ATTRIBUTE_PRIVATE, but
> > the invalidation should be necessary yet for attribute change of:
> >
> > KVM_MEMORY_ATTRIBUTE_READ
> > KVM_MEMORY_ATTRIBUTE_WRITE
> > KVM_MEMORY_ATTRIBUTE_EXECUTE
>
> The unmapping is only needed for confidential usages which uses
> KVM_MEMORY_ATTRIBUTE_PRIVATE only and the other flags are defined here
> for other usages like pKVM. As Fuad commented in a different reply, pKVM
> supports in-place remapping and unmapping is unnecessary.

Ah, I see. It's fine to me, thanks.

>
> Thanks,
> Chao
> >
> > > +		KVM_MMU_UNLOCK(kvm);
> > > +	}
> > > +
> > >  	mutex_lock(&kvm->lock);
> > >  	for (i = start; i < end; i++)
> > >  		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > > @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > >  			break;
> > >  	mutex_unlock(&kvm->lock);
> > >
> > > +	if (kvm_arch_has_private_mem(kvm)) {
> > > +		idx = srcu_read_lock(&kvm->srcu);
> > > +		KVM_MMU_LOCK(kvm);
> > > +		if (i > start)
> > > +			kvm_unmap_mem_range(kvm, start, i);
> > > +		kvm_mmu_invalidate_end(kvm);
> >
> > Ditto.
> >
> > > +		KVM_MMU_UNLOCK(kvm);
> > > +		srcu_read_unlock(&kvm->srcu, idx);
> > > +	}
> > > +
> > >  	attrs->address = i << PAGE_SHIFT;
> > >  	attrs->size = (end - i) << PAGE_SHIFT;
> > >
> > > --
> > > 2.25.1
> > >
> > >

Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

[Yuan Yao]

On Thu, Dec 08, 2022 at 07:23:46PM +0800, Chao Peng wrote:
> On Thu, Dec 08, 2022 at 10:29:18AM +0800, Yuan Yao wrote:
> > On Fri, Dec 02, 2022 at 02:13:46PM +0800, Chao Peng wrote:
> > > A KVM_MEM_PRIVATE memslot can include both fd-based private memory and
> > > hva-based shared memory. Architecture code (like TDX code) can tell
> > > whether the on-going fault is private or not. This patch adds a
> > > 'is_private' field to kvm_page_fault to indicate this and architecture
> > > code is expected to set it.
> > >
> > > To handle page fault for such memslot, the handling logic is different
> > > depending on whether the fault is private or shared. KVM checks if
> > > 'is_private' matches the host's view of the page (maintained in
> > > mem_attr_array).
> > >   - For a successful match, private pfn is obtained with
> > >     restrictedmem_get_page() and shared pfn is obtained with existing
> > >     get_user_pages().
> > >   - For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
> > >     userspace. Userspace then can convert memory between private/shared
> > >     in host's view and retry the fault.
> > >
> > > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > ---
> > >  arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++++++++++++++--
> > >  arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
> > >  arch/x86/kvm/mmu/mmutrace.h     |  1 +
> > >  arch/x86/kvm/mmu/tdp_mmu.c      |  2 +-
> > >  include/linux/kvm_host.h        | 30 ++++++++++++++++
> > >  5 files changed, 105 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > index 2190fd8c95c0..b1953ebc012e 100644
> > > --- a/arch/x86/kvm/mmu/mmu.c
> > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > @@ -3058,7 +3058,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
> > >
> > >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> > >  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> > > -			      int max_level)
> > > +			      int max_level, bool is_private)
> > >  {
> > >  	struct kvm_lpage_info *linfo;
> > >  	int host_level;
> > > @@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> > >  			break;
> > >  	}
> > >
> > > +	if (is_private)
> > > +		return max_level;
> >
> > lpage mixed information already saved, so is that possible
> > to query info->disallow_lpage without care 'is_private' ?
>
> Actually we already queried info->disallow_lpage just before this
> sentence. The check is needed because later in the function we call
> host_pfn_mapping_level() which is shared memory specific.

You're right. We can't get mapping level info for private page from
host_pfn_mapping_level().

>
> Thanks,
> Chao
> >
> > > +
> > >  	if (max_level == PG_LEVEL_4K)
> > >  		return PG_LEVEL_4K;
> > >
> > > @@ -3098,7 +3101,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> > >  	 * level, which will be used to do precise, accurate accounting.
> > >  	 */
> > >  	fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> > > -						     fault->gfn, fault->max_level);
> > > +						     fault->gfn, fault->max_level,
> > > +						     fault->is_private);
> > >  	if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
> > >  		return;
> > >
> > > @@ -4178,6 +4182,49 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> > >  	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
> > >  }
> > >
> > > +static inline u8 order_to_level(int order)
> > > +{
> > > +	BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> > > +
> > > +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> > > +		return PG_LEVEL_1G;
> > > +
> > > +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> > > +		return PG_LEVEL_2M;
> > > +
> > > +	return PG_LEVEL_4K;
> > > +}
> > > +
> > > +static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> > > +				    struct kvm_page_fault *fault)
> > > +{
> > > +	vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> > > +	if (fault->is_private)
> > > +		vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> > > +	else
> > > +		vcpu->run->memory.flags = 0;
> > > +	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> > > +	vcpu->run->memory.size = PAGE_SIZE;
> > > +	return RET_PF_USER;
> > > +}
> > > +
> > > +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> > > +				   struct kvm_page_fault *fault)
> > > +{
> > > +	int order;
> > > +	struct kvm_memory_slot *slot = fault->slot;
> > > +
> > > +	if (!kvm_slot_can_be_private(slot))
> > > +		return kvm_do_memory_fault_exit(vcpu, fault);
> > > +
> > > +	if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> > > +		return RET_PF_RETRY;
> > > +
> > > +	fault->max_level = min(order_to_level(order), fault->max_level);
> > > +	fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
> > > +	return RET_PF_CONTINUE;
> > > +}
> > > +
> > >  static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > >  {
> > >  	struct kvm_memory_slot *slot = fault->slot;
> > > @@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > >  			return RET_PF_EMULATE;
> > >  	}
> > >
> > > +	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> > > +		return kvm_do_memory_fault_exit(vcpu, fault);
> > > +
> > > +	if (fault->is_private)
> > > +		return kvm_faultin_pfn_private(vcpu, fault);
> > > +
> > >  	async = false;
> > >  	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
> > >  					  fault->write, &fault->map_writable,
> > > @@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
> > >  			return -EIO;
> > >  	}
> > >
> > > +	if (r == RET_PF_USER)
> > > +		return 0;
> > > +
> > >  	if (r < 0)
> > >  		return r;
> > >  	if (r != RET_PF_EMULATE)
> > > @@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> > >  		 */
> > >  		if (sp->role.direct &&
> > >  		    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> > > -							       PG_LEVEL_NUM)) {
> > > +							       PG_LEVEL_NUM,
> > > +							       false)) {
> > >  			kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
> > >
> > >  			if (kvm_available_flush_tlb_with_range())
> > > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> > > index dbaf6755c5a7..5ccf08183b00 100644
> > > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > > @@ -189,6 +189,7 @@ struct kvm_page_fault {
> > >
> > >  	/* Derived from mmu and global state.  */
> > >  	const bool is_tdp;
> > > +	const bool is_private;
> > >  	const bool nx_huge_page_workaround_enabled;
> > >
> > >  	/*
> > > @@ -237,6 +238,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> > >   * RET_PF_RETRY: let CPU fault again on the address.
> > >   * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
> > >   * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
> > > + * RET_PF_USER: need to exit to userspace to handle this fault.
> > >   * RET_PF_FIXED: The faulting entry has been fixed.
> > >   * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
> > >   *
> > > @@ -253,6 +255,7 @@ enum {
> > >  	RET_PF_RETRY,
> > >  	RET_PF_EMULATE,
> > >  	RET_PF_INVALID,
> > > +	RET_PF_USER,
> > >  	RET_PF_FIXED,
> > >  	RET_PF_SPURIOUS,
> > >  };
> > > @@ -310,7 +313,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > >
> > >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> > >  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> > > -			      int max_level);
> > > +			      int max_level, bool is_private);
> > >  void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> > >  void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
> > >
> > > @@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> > >  void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> > >  void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> > >
> > > +#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > > +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > > +{
> > > +	WARN_ON_ONCE(1);
> > > +	return -EOPNOTSUPP;
> > > +}
> > > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > > +
> > >  #endif /* __KVM_X86_MMU_INTERNAL_H */
> > > diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> > > index ae86820cef69..2d7555381955 100644
> > > --- a/arch/x86/kvm/mmu/mmutrace.h
> > > +++ b/arch/x86/kvm/mmu/mmutrace.h
> > > @@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
> > >  TRACE_DEFINE_ENUM(RET_PF_RETRY);
> > >  TRACE_DEFINE_ENUM(RET_PF_EMULATE);
> > >  TRACE_DEFINE_ENUM(RET_PF_INVALID);
> > > +TRACE_DEFINE_ENUM(RET_PF_USER);
> > >  TRACE_DEFINE_ENUM(RET_PF_FIXED);
> > >  TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
> > >
> > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > > index 771210ce5181..8ba1a4afc546 100644
> > > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > > @@ -1768,7 +1768,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
> > >  			continue;
> > >
> > >  		max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
> > > -							      iter.gfn, PG_LEVEL_NUM);
> > > +						iter.gfn, PG_LEVEL_NUM, false);
> > >  		if (max_mapping_level < iter.level)
> > >  			continue;
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 25099c94e770..153842bb33df 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> > >  }
> > >  #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
> > >
> > > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > > +{
> > > +	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> > > +	       KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > > +}
> > > +#else
> > > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > > +{
> > > +	return false;
> > > +}
> > > +
> > > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > > +
> > > +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > > +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > > +{
> > > +	int ret;
> > > +	struct page *page;
> > > +	pgoff_t index = gfn - slot->base_gfn +
> > > +			(slot->restricted_offset >> PAGE_SHIFT);
> > > +
> > > +	ret = restrictedmem_get_page(slot->restricted_file, index,
> > > +				     &page, order);
> > > +	*pfn = page_to_pfn(page);
> > > +	return ret;
> > > +}
> > > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > > +
> > >  #endif
> > > --
> > > 2.25.1
> > >
> > >

Re: [PATCH v10 5/9] KVM: Use gfn instead of hva for mmu_notifier_retry

[Chao Peng]

On Tue, Dec 06, 2022 at 03:48:50PM +0000, Fuad Tabba wrote:
...
 > >
> > > >          */
> > > > -       if (unlikely(kvm->mmu_invalidate_in_progress) &&
> > > > -           hva >= kvm->mmu_invalidate_range_start &&
> > > > -           hva < kvm->mmu_invalidate_range_end)
> > > > -               return 1;
> > > > +       if (unlikely(kvm->mmu_invalidate_in_progress)) {
> > > > +               /*
> > > > +                * Dropping mmu_lock after bumping mmu_invalidate_in_progress
> > > > +                * but before updating the range is a KVM bug.
> > > > +                */
> > > > +               if (WARN_ON_ONCE(kvm->mmu_invalidate_range_start == INVALID_GPA ||
> > > > +                                kvm->mmu_invalidate_range_end == INVALID_GPA))
> > >
> > > INVALID_GPA is an x86-specific define in
> > > arch/x86/include/asm/kvm_host.h, so this doesn't build on other
> > > architectures. The obvious fix is to move it to
> > > include/linux/kvm_host.h.
> >
> > Hmm, INVALID_GPA is defined as ZERO for x86, not 100% confident this is
> > correct choice for other architectures, but after search it has not been
> > used for other architectures, so should be safe to make it common.

As Yu posted a patch:
https://lore.kernel.org/all/20221209023622.274715-1-yu.c.zhang@linux.intel.com/

There is a GPA_INVALID in include/linux/kvm_types.h and I see ARM has already
been using it so sounds that is exactly what I need.

Chao
> 
> With this fixed,
> 
> Reviewed-by: Fuad Tabba <tabba@google.com>
> And the necessary work to port to arm64 (on qemu/arm64):
> Tested-by: Fuad Tabba <tabba@google.com>
> 
> Cheers,
> /fuad

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Fuad Tabba]

Hi,

On Thu, Dec 8, 2022 at 11:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> On Wed, Dec 07, 2022 at 05:16:34PM +0000, Fuad Tabba wrote:
> > Hi,
> >
> > On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > >
> > > Unmap the existing guest mappings when memory attribute is changed
> > > between shared and private. This is needed because shared pages and
> > > private pages are from different backends, unmapping existing ones
> > > gives a chance for page fault handler to re-populate the mappings
> > > according to the new attribute.
> > >
> > > Only architecture has private memory support needs this and the
> > > supported architecture is expected to rewrite the weak
> > > kvm_arch_has_private_mem().
> >
> > This kind of ties into the discussion of being able to share memory in
> > place. For pKVM for example, shared and private memory would have the
> > same backend, and the unmapping wouldn't be needed.
> >
> > So I guess that, instead of kvm_arch_has_private_mem(), can the check
> > be done differently, e.g., with a different function, say
> > kvm_arch_private_notify_attribute_change() (but maybe with a more
> > friendly name than what I suggested :) )?
>
> Besides controlling the unmapping here, kvm_arch_has_private_mem() is
> also used to gate the memslot KVM_MEM_PRIVATE flag in patch09. I know
> unmapping is confirmed unnecessary for pKVM, but how about
> KVM_MEM_PRIVATE? Will pKVM add its own flag or reuse KVM_MEM_PRIVATE?
> If the answer is the latter, then yes we should use a different check
> which only works for confidential usages here.

I think it makes sense for pKVM to use the same flag (KVM_MEM_PRIVATE)
and not to add another one.

Thank you,
/fuad



>
> Thanks,
> Chao
> >
> > Thanks,
> > /fuad
> >
> > >
> > > Also, during memory attribute changing and the unmapping time frame,
> > > page fault handler may happen in the same memory range and can cause
> > > incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> > > page fault handler retry during this time frame.
> > >
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > ---
> > >  include/linux/kvm_host.h |   7 +-
> > >  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
> > >  2 files changed, 116 insertions(+), 59 deletions(-)
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 3d69484d2704..3331c0c92838 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > >  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> > >  #endif
> > >
> > > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > >  struct kvm_gfn_range {
> > >         struct kvm_memory_slot *slot;
> > >         gfn_t start;
> > > @@ -264,6 +263,8 @@ struct kvm_gfn_range {
> > >         bool may_block;
> > >  };
> > >  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> > > +
> > > +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > >  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > >  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > >  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > > @@ -785,11 +786,12 @@ struct kvm {
> > >
> > >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> > >         struct mmu_notifier mmu_notifier;
> > > +#endif
> > >         unsigned long mmu_invalidate_seq;
> > >         long mmu_invalidate_in_progress;
> > >         gfn_t mmu_invalidate_range_start;
> > >         gfn_t mmu_invalidate_range_end;
> > > -#endif
> > > +
> > >         struct list_head devices;
> > >         u64 manual_dirty_log_protect;
> > >         struct dentry *debugfs_dentry;
> > > @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> > >  int kvm_arch_post_init_vm(struct kvm *kvm);
> > >  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> > >  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> > > +bool kvm_arch_has_private_mem(struct kvm *kvm);
> > >
> > >  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> > >  /*
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index ad55dfbc75d7..4e1e1e113bf0 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
> > >  }
> > >  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
> > >
> > > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > +{
> > > +       /*
> > > +        * The count increase must become visible at unlock time as no
> > > +        * spte can be established without taking the mmu_lock and
> > > +        * count is also read inside the mmu_lock critical section.
> > > +        */
> > > +       kvm->mmu_invalidate_in_progress++;
> > > +
> > > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > +               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > +               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > +       }
> > > +}
> > > +
> > > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > > +{
> > > +       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > +
> > > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > +               kvm->mmu_invalidate_range_start = start;
> > > +               kvm->mmu_invalidate_range_end = end;
> > > +       } else {
> > > +               /*
> > > +                * Fully tracking multiple concurrent ranges has diminishing
> > > +                * returns. Keep things simple and just find the minimal range
> > > +                * which includes the current and new ranges. As there won't be
> > > +                * enough information to subtract a range after its invalidate
> > > +                * completes, any ranges invalidated concurrently will
> > > +                * accumulate and persist until all outstanding invalidates
> > > +                * complete.
> > > +                */
> > > +               kvm->mmu_invalidate_range_start =
> > > +                       min(kvm->mmu_invalidate_range_start, start);
> > > +               kvm->mmu_invalidate_range_end =
> > > +                       max(kvm->mmu_invalidate_range_end, end);
> > > +       }
> > > +}
> > > +
> > > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > +{
> > > +       /*
> > > +        * This sequence increase will notify the kvm page fault that
> > > +        * the page that is going to be mapped in the spte could have
> > > +        * been freed.
> > > +        */
> > > +       kvm->mmu_invalidate_seq++;
> > > +       smp_wmb();
> > > +       /*
> > > +        * The above sequence increase must be visible before the
> > > +        * below count decrease, which is ensured by the smp_wmb above
> > > +        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > > +        */
> > > +       kvm->mmu_invalidate_in_progress--;
> > > +}
> > > +
> > >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> > >  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
> > >  {
> > > @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> > >         kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> > >  }
> > >
> > > -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > -{
> > > -       /*
> > > -        * The count increase must become visible at unlock time as no
> > > -        * spte can be established without taking the mmu_lock and
> > > -        * count is also read inside the mmu_lock critical section.
> > > -        */
> > > -       kvm->mmu_invalidate_in_progress++;
> > > -
> > > -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > -               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > -               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > -       }
> > > -}
> > > -
> > > -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > > -{
> > > -       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > -
> > > -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > -               kvm->mmu_invalidate_range_start = start;
> > > -               kvm->mmu_invalidate_range_end = end;
> > > -       } else {
> > > -               /*
> > > -                * Fully tracking multiple concurrent ranges has diminishing
> > > -                * returns. Keep things simple and just find the minimal range
> > > -                * which includes the current and new ranges. As there won't be
> > > -                * enough information to subtract a range after its invalidate
> > > -                * completes, any ranges invalidated concurrently will
> > > -                * accumulate and persist until all outstanding invalidates
> > > -                * complete.
> > > -                */
> > > -               kvm->mmu_invalidate_range_start =
> > > -                       min(kvm->mmu_invalidate_range_start, start);
> > > -               kvm->mmu_invalidate_range_end =
> > > -                       max(kvm->mmu_invalidate_range_end, end);
> > > -       }
> > > -}
> > > -
> > >  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> > >  {
> > >         kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > > @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> > >         return 0;
> > >  }
> > >
> > > -void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > -{
> > > -       /*
> > > -        * This sequence increase will notify the kvm page fault that
> > > -        * the page that is going to be mapped in the spte could have
> > > -        * been freed.
> > > -        */
> > > -       kvm->mmu_invalidate_seq++;
> > > -       smp_wmb();
> > > -       /*
> > > -        * The above sequence increase must be visible before the
> > > -        * below count decrease, which is ensured by the smp_wmb above
> > > -        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > > -        */
> > > -       kvm->mmu_invalidate_in_progress--;
> > > -}
> > > -
> > >  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> > >                                         const struct mmu_notifier_range *range)
> > >  {
> > > @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
> > >         return 0;
> > >  }
> > >
> > > +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> > > +{
> > > +       return false;
> > > +}
> > > +
> > >  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> > >  {
> > >         struct kvm *kvm = kvm_arch_alloc_vm();
> > > @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> > >         return 0;
> > >  }
> > >
> > > +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> > > +{
> > > +       struct kvm_gfn_range gfn_range;
> > > +       struct kvm_memory_slot *slot;
> > > +       struct kvm_memslots *slots;
> > > +       struct kvm_memslot_iter iter;
> > > +       int i;
> > > +       int r = 0;
> > > +
> > > +       gfn_range.pte = __pte(0);
> > > +       gfn_range.may_block = true;
> > > +
> > > +       for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > > +               slots = __kvm_memslots(kvm, i);
> > > +
> > > +               kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> > > +                       slot = iter.slot;
> > > +                       gfn_range.start = max(start, slot->base_gfn);
> > > +                       gfn_range.end = min(end, slot->base_gfn + slot->npages);
> > > +                       if (gfn_range.start >= gfn_range.end)
> > > +                               continue;
> > > +                       gfn_range.slot = slot;
> > > +
> > > +                       r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> > > +               }
> > > +       }
> > > +
> > > +       if (r)
> > > +               kvm_flush_remote_tlbs(kvm);
> > > +}
> > > +
> > >  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > >                                            struct kvm_memory_attributes *attrs)
> > >  {
> > >         gfn_t start, end;
> > >         unsigned long i;
> > >         void *entry;
> > > +       int idx;
> > >         u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > >
> > > -       /* flags is currently not used. */
> > > +       /* 'flags' is currently not used. */
> > >         if (attrs->flags)
> > >                 return -EINVAL;
> > >         if (attrs->attributes & ~supported_attrs)
> > > @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > >
> > >         entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > >
> > > +       if (kvm_arch_has_private_mem(kvm)) {
> > > +               KVM_MMU_LOCK(kvm);
> > > +               kvm_mmu_invalidate_begin(kvm);
> > > +               kvm_mmu_invalidate_range_add(kvm, start, end);
> > > +               KVM_MMU_UNLOCK(kvm);
> > > +       }
> > > +
> > >         mutex_lock(&kvm->lock);
> > >         for (i = start; i < end; i++)
> > >                 if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > > @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > >                         break;
> > >         mutex_unlock(&kvm->lock);
> > >
> > > +       if (kvm_arch_has_private_mem(kvm)) {
> > > +               idx = srcu_read_lock(&kvm->srcu);
> > > +               KVM_MMU_LOCK(kvm);
> > > +               if (i > start)
> > > +                       kvm_unmap_mem_range(kvm, start, i);
> > > +               kvm_mmu_invalidate_end(kvm);
> > > +               KVM_MMU_UNLOCK(kvm);
> > > +               srcu_read_unlock(&kvm->srcu, idx);
> > > +       }
> > > +
> > >         attrs->address = i << PAGE_SHIFT;
> > >         attrs->size = (end - i) << PAGE_SHIFT;
> > >
> > > --
> > > 2.25.1
> > >

Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

[Fuad Tabba]

Hi,

On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> A KVM_MEM_PRIVATE memslot can include both fd-based private memory and
> hva-based shared memory. Architecture code (like TDX code) can tell
> whether the on-going fault is private or not. This patch adds a
> 'is_private' field to kvm_page_fault to indicate this and architecture
> code is expected to set it.
>
> To handle page fault for such memslot, the handling logic is different
> depending on whether the fault is private or shared. KVM checks if
> 'is_private' matches the host's view of the page (maintained in
> mem_attr_array).
>   - For a successful match, private pfn is obtained with
>     restrictedmem_get_page() and shared pfn is obtained with existing
>     get_user_pages().
>   - For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
>     userspace. Userspace then can convert memory between private/shared
>     in host's view and retry the fault.
>
> Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++++++++++++++--
>  arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
>  arch/x86/kvm/mmu/mmutrace.h     |  1 +
>  arch/x86/kvm/mmu/tdp_mmu.c      |  2 +-
>  include/linux/kvm_host.h        | 30 ++++++++++++++++
>  5 files changed, 105 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 2190fd8c95c0..b1953ebc012e 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3058,7 +3058,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
>
>  int kvm_mmu_max_mapping_level(struct kvm *kvm,
>                               const struct kvm_memory_slot *slot, gfn_t gfn,
> -                             int max_level)
> +                             int max_level, bool is_private)
>  {
>         struct kvm_lpage_info *linfo;
>         int host_level;
> @@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
>                         break;
>         }
>
> +       if (is_private)
> +               return max_level;
> +
>         if (max_level == PG_LEVEL_4K)
>                 return PG_LEVEL_4K;
>
> @@ -3098,7 +3101,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>          * level, which will be used to do precise, accurate accounting.
>          */
>         fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> -                                                    fault->gfn, fault->max_level);
> +                                                    fault->gfn, fault->max_level,
> +                                                    fault->is_private);
>         if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
>                 return;
>
> @@ -4178,6 +4182,49 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>         kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
>  }
>
> +static inline u8 order_to_level(int order)
> +{
> +       BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> +
> +       if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> +               return PG_LEVEL_1G;
> +
> +       if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> +               return PG_LEVEL_2M;
> +
> +       return PG_LEVEL_4K;
> +}
> +
> +static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> +                                   struct kvm_page_fault *fault)
> +{
> +       vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> +       if (fault->is_private)
> +               vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> +       else
> +               vcpu->run->memory.flags = 0;
> +       vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;

nit: As in previous patches, use helpers (for this and other similar
shifts in this patch)?

> +       vcpu->run->memory.size = PAGE_SIZE;
> +       return RET_PF_USER;
> +}
> +
> +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> +                                  struct kvm_page_fault *fault)
> +{
> +       int order;
> +       struct kvm_memory_slot *slot = fault->slot;
> +
> +       if (!kvm_slot_can_be_private(slot))
> +               return kvm_do_memory_fault_exit(vcpu, fault);
> +
> +       if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> +               return RET_PF_RETRY;
> +
> +       fault->max_level = min(order_to_level(order), fault->max_level);
> +       fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
> +       return RET_PF_CONTINUE;
> +}
> +
>  static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  {
>         struct kvm_memory_slot *slot = fault->slot;
> @@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>                         return RET_PF_EMULATE;
>         }
>
> +       if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> +               return kvm_do_memory_fault_exit(vcpu, fault);
> +
> +       if (fault->is_private)
> +               return kvm_faultin_pfn_private(vcpu, fault);
> +
>         async = false;
>         fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
>                                           fault->write, &fault->map_writable,
> @@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
>                         return -EIO;
>         }
>
> +       if (r == RET_PF_USER)
> +               return 0;
> +
>         if (r < 0)
>                 return r;
>         if (r != RET_PF_EMULATE)
> @@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>                  */
>                 if (sp->role.direct &&
>                     sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> -                                                              PG_LEVEL_NUM)) {
> +                                                              PG_LEVEL_NUM,
> +                                                              false)) {
>                         kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
>
>                         if (kvm_available_flush_tlb_with_range())
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index dbaf6755c5a7..5ccf08183b00 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -189,6 +189,7 @@ struct kvm_page_fault {
>
>         /* Derived from mmu and global state.  */
>         const bool is_tdp;
> +       const bool is_private;
>         const bool nx_huge_page_workaround_enabled;
>
>         /*
> @@ -237,6 +238,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
>   * RET_PF_RETRY: let CPU fault again on the address.
>   * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
>   * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
> + * RET_PF_USER: need to exit to userspace to handle this fault.
>   * RET_PF_FIXED: The faulting entry has been fixed.
>   * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
>   *
> @@ -253,6 +255,7 @@ enum {
>         RET_PF_RETRY,
>         RET_PF_EMULATE,
>         RET_PF_INVALID,
> +       RET_PF_USER,
>         RET_PF_FIXED,
>         RET_PF_SPURIOUS,
>  };
> @@ -310,7 +313,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>
>  int kvm_mmu_max_mapping_level(struct kvm *kvm,
>                               const struct kvm_memory_slot *slot, gfn_t gfn,
> -                             int max_level);
> +                             int max_level, bool is_private);
>  void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
>  void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
>
> @@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
>  void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
>  void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
>
> +#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> +                                       gfn_t gfn, kvm_pfn_t *pfn, int *order)
> +{
> +       WARN_ON_ONCE(1);
> +       return -EOPNOTSUPP;
> +}
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
>  #endif /* __KVM_X86_MMU_INTERNAL_H */
> diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> index ae86820cef69..2d7555381955 100644
> --- a/arch/x86/kvm/mmu/mmutrace.h
> +++ b/arch/x86/kvm/mmu/mmutrace.h
> @@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
>  TRACE_DEFINE_ENUM(RET_PF_RETRY);
>  TRACE_DEFINE_ENUM(RET_PF_EMULATE);
>  TRACE_DEFINE_ENUM(RET_PF_INVALID);
> +TRACE_DEFINE_ENUM(RET_PF_USER);
>  TRACE_DEFINE_ENUM(RET_PF_FIXED);
>  TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 771210ce5181..8ba1a4afc546 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1768,7 +1768,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
>                         continue;
>
>                 max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
> -                                                             iter.gfn, PG_LEVEL_NUM);
> +                                               iter.gfn, PG_LEVEL_NUM, false);
>                 if (max_mapping_level < iter.level)
>                         continue;
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 25099c94e770..153842bb33df 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
>  }
>  #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
>
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{
> +       return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> +              KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +}
> +#else
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{
> +       return false;
> +}
> +
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +
> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> +                                       gfn_t gfn, kvm_pfn_t *pfn, int *order)
> +{
> +       int ret;
> +       struct page *page;
> +       pgoff_t index = gfn - slot->base_gfn +
> +                       (slot->restricted_offset >> PAGE_SHIFT);
> +
> +       ret = restrictedmem_get_page(slot->restricted_file, index,
> +                                    &page, order);
> +       *pfn = page_to_pfn(page);
> +       return ret;
> +}
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
>  #endif
> --
> 2.25.1
>

With my limited understanding of x86 code:
Reviewed-by: Fuad Tabba <tabba@google.com>

The common code in kvm_host.h was used in the port to arm64, and the
x86 fault handling code was used as a guide to how it should be done
in pKVM (with similar code added there). So with these caveats in
mind:
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Fuad Tabba]

Hi,

On Fri, Dec 2, 2022 at 6:20 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> Register/unregister private memslot to fd-based memory backing store
> restrictedmem and implement the callbacks for restrictedmem_notifier:
>   - invalidate_start()/invalidate_end() to zap the existing memory
>     mappings in the KVM page table.
>   - error() to request KVM_REQ_MEMORY_MCE and later exit to userspace
>     with KVM_EXIT_SHUTDOWN.
>
> Expose KVM_MEM_PRIVATE for memslot and KVM_MEMORY_ATTRIBUTE_PRIVATE for
> KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to userspace but either are
> controlled by kvm_arch_has_private_mem() which should be rewritten by
> architecture code.
>
> Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>

With the code to port it to pKVM/arm64:
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad


> ---
>  arch/x86/include/asm/kvm_host.h |   1 +
>  arch/x86/kvm/x86.c              |  13 +++
>  include/linux/kvm_host.h        |   3 +
>  virt/kvm/kvm_main.c             | 179 +++++++++++++++++++++++++++++++-
>  4 files changed, 191 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 7772ab37ac89..27ef31133352 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -114,6 +114,7 @@
>         KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
>  #define KVM_REQ_HV_TLB_FLUSH \
>         KVM_ARCH_REQ_FLAGS(32, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> +#define KVM_REQ_MEMORY_MCE             KVM_ARCH_REQ(33)
>
>  #define CR0_RESERVED_BITS                                               \
>         (~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5aefcff614d2..c67e22f3e2ee 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6587,6 +6587,13 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned long state)
>  }
>  #endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */
>
> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +void kvm_arch_memory_mce(struct kvm *kvm)
> +{
> +       kvm_make_all_cpus_request(kvm, KVM_REQ_MEMORY_MCE);
> +}
> +#endif
> +
>  static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp)
>  {
>         struct kvm_clock_data data = { 0 };
> @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>
>                 if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
>                         static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> +
> +               if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> +                       vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> +                       r = 0;
> +                       goto out;
> +               }
>         }
>
>         if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 153842bb33df..f032d878e034 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -590,6 +590,7 @@ struct kvm_memory_slot {
>         struct file *restricted_file;
>         loff_t restricted_offset;
>         struct restrictedmem_notifier notifier;
> +       struct kvm *kvm;
>  };
>
>  static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
> @@ -2363,6 +2364,8 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
>         *pfn = page_to_pfn(page);
>         return ret;
>  }
> +
> +void kvm_arch_memory_mce(struct kvm *kvm);
>  #endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
>
>  #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e107afea32f0..ac835fc77273 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -936,6 +936,121 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
>
>  #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
>
> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
> +                                        pgoff_t start, pgoff_t end,
> +                                        gfn_t *gfn_start, gfn_t *gfn_end)
> +{
> +       unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> +
> +       if (start > base_pgoff)
> +               *gfn_start = slot->base_gfn + start - base_pgoff;
> +       else
> +               *gfn_start = slot->base_gfn;
> +
> +       if (end < base_pgoff + slot->npages)
> +               *gfn_end = slot->base_gfn + end - base_pgoff;
> +       else
> +               *gfn_end = slot->base_gfn + slot->npages;
> +
> +       if (*gfn_start >= *gfn_end)
> +               return false;
> +
> +       return true;
> +}
> +
> +static void kvm_restrictedmem_invalidate_begin(struct restrictedmem_notifier *notifier,
> +                                              pgoff_t start, pgoff_t end)
> +{
> +       struct kvm_memory_slot *slot = container_of(notifier,
> +                                                   struct kvm_memory_slot,
> +                                                   notifier);
> +       struct kvm *kvm = slot->kvm;
> +       gfn_t gfn_start, gfn_end;
> +       struct kvm_gfn_range gfn_range;
> +       int idx;
> +
> +       if (!restrictedmem_range_is_valid(slot, start, end,
> +                                         &gfn_start, &gfn_end))
> +               return;
> +
> +       gfn_range.start = gfn_start;
> +       gfn_range.end = gfn_end;
> +       gfn_range.slot = slot;
> +       gfn_range.pte = __pte(0);
> +       gfn_range.may_block = true;
> +
> +       idx = srcu_read_lock(&kvm->srcu);
> +       KVM_MMU_LOCK(kvm);
> +
> +       kvm_mmu_invalidate_begin(kvm);
> +       kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
> +       if (kvm_unmap_gfn_range(kvm, &gfn_range))
> +               kvm_flush_remote_tlbs(kvm);
> +
> +       KVM_MMU_UNLOCK(kvm);
> +       srcu_read_unlock(&kvm->srcu, idx);
> +}
> +
> +static void kvm_restrictedmem_invalidate_end(struct restrictedmem_notifier *notifier,
> +                                            pgoff_t start, pgoff_t end)
> +{
> +       struct kvm_memory_slot *slot = container_of(notifier,
> +                                                   struct kvm_memory_slot,
> +                                                   notifier);
> +       struct kvm *kvm = slot->kvm;
> +       gfn_t gfn_start, gfn_end;
> +
> +       if (!restrictedmem_range_is_valid(slot, start, end,
> +                                         &gfn_start, &gfn_end))
> +               return;
> +
> +       KVM_MMU_LOCK(kvm);
> +       kvm_mmu_invalidate_end(kvm);
> +       KVM_MMU_UNLOCK(kvm);
> +}
> +
> +static void kvm_restrictedmem_error(struct restrictedmem_notifier *notifier,
> +                                   pgoff_t start, pgoff_t end)
> +{
> +       struct kvm_memory_slot *slot = container_of(notifier,
> +                                                   struct kvm_memory_slot,
> +                                                   notifier);
> +       kvm_arch_memory_mce(slot->kvm);
> +}
> +
> +static struct restrictedmem_notifier_ops kvm_restrictedmem_notifier_ops = {
> +       .invalidate_start = kvm_restrictedmem_invalidate_begin,
> +       .invalidate_end = kvm_restrictedmem_invalidate_end,
> +       .error = kvm_restrictedmem_error,
> +};
> +
> +static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
> +{
> +       slot->notifier.ops = &kvm_restrictedmem_notifier_ops;
> +       restrictedmem_register_notifier(slot->restricted_file, &slot->notifier);
> +}
> +
> +static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
> +{
> +       restrictedmem_unregister_notifier(slot->restricted_file,
> +                                         &slot->notifier);
> +}
> +
> +#else /* !CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
> +static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
> +{
> +       WARN_ON_ONCE(1);
> +}
> +
> +static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
> +{
> +       WARN_ON_ONCE(1);
> +}
> +
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
>  #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
>  static int kvm_pm_notifier_call(struct notifier_block *bl,
>                                 unsigned long state,
> @@ -980,6 +1095,11 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
>  /* This does not remove the slot from struct kvm_memslots data structures */
>  static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
>  {
> +       if (slot->flags & KVM_MEM_PRIVATE) {
> +               kvm_restrictedmem_unregister(slot);
> +               fput(slot->restricted_file);
> +       }
> +
>         kvm_destroy_dirty_bitmap(slot);
>
>         kvm_arch_free_memslot(kvm, slot);
> @@ -1551,10 +1671,14 @@ static void kvm_replace_memslot(struct kvm *kvm,
>         }
>  }
>
> -static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> +static int check_memory_region_flags(struct kvm *kvm,
> +                                    const struct kvm_user_mem_region *mem)
>  {
>         u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
>
> +       if (kvm_arch_has_private_mem(kvm))
> +               valid_flags |= KVM_MEM_PRIVATE;
> +
>  #ifdef __KVM_HAVE_READONLY_MEM
>         valid_flags |= KVM_MEM_READONLY;
>  #endif
> @@ -1630,6 +1754,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
>  {
>         int r;
>
> +       if (change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
> +               kvm_restrictedmem_register(new);
> +
>         /*
>          * If dirty logging is disabled, nullify the bitmap; the old bitmap
>          * will be freed on "commit".  If logging is enabled in both old and
> @@ -1658,6 +1785,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
>         if (r && new && new->dirty_bitmap && (!old || !old->dirty_bitmap))
>                 kvm_destroy_dirty_bitmap(new);
>
> +       if (r && change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
> +               kvm_restrictedmem_unregister(new);
> +
>         return r;
>  }
>
> @@ -1963,7 +2093,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>         int as_id, id;
>         int r;
>
> -       r = check_memory_region_flags(mem);
> +       r = check_memory_region_flags(kvm, mem);
>         if (r)
>                 return r;
>
> @@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
>              !access_ok((void __user *)(unsigned long)mem->userspace_addr,
>                         mem->memory_size))
>                 return -EINVAL;
> +       if (mem->flags & KVM_MEM_PRIVATE &&
> +               (mem->restricted_offset & (PAGE_SIZE - 1) ||
> +                mem->restricted_offset > U64_MAX - mem->memory_size))
> +               return -EINVAL;
>         if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
>                 return -EINVAL;
>         if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
>                 if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
>                         return -EINVAL;
>         } else { /* Modify an existing slot. */
> +               /* Private memslots are immutable, they can only be deleted. */
> +               if (mem->flags & KVM_MEM_PRIVATE)
> +                       return -EINVAL;
>                 if ((mem->userspace_addr != old->userspace_addr) ||
>                     (npages != old->npages) ||
>                     ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
>         new->npages = npages;
>         new->flags = mem->flags;
>         new->userspace_addr = mem->userspace_addr;
> +       if (mem->flags & KVM_MEM_PRIVATE) {
> +               new->restricted_file = fget(mem->restricted_fd);
> +               if (!new->restricted_file ||
> +                   !file_is_restrictedmem(new->restricted_file)) {
> +                       r = -EINVAL;
> +                       goto out;
> +               }
> +               new->restricted_offset = mem->restricted_offset;
> +       }
> +
> +       new->kvm = kvm;
>
>         r = kvm_set_memslot(kvm, old, new, change);
>         if (r)
> -               kfree(new);
> +               goto out;
> +
> +       return 0;
> +
> +out:
> +       if (new->restricted_file)
> +               fput(new->restricted_file);
> +       kfree(new);
>         return r;
>  }
>  EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> @@ -2351,6 +2506,8 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
>  #ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
>  static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>  {
> +       if (kvm_arch_has_private_mem(kvm))
> +               return KVM_MEMORY_ATTRIBUTE_PRIVATE;
>         return 0;
>  }
>
> @@ -4822,16 +4979,28 @@ static long kvm_vm_ioctl(struct file *filp,
>         }
>         case KVM_SET_USER_MEMORY_REGION: {
>                 struct kvm_user_mem_region mem;
> -               unsigned long size = sizeof(struct kvm_userspace_memory_region);
> +               unsigned int flags_offset = offsetof(typeof(mem), flags);
> +               unsigned long size;
> +               u32 flags;
>
>                 kvm_sanity_check_user_mem_region_alias();
>
> +               memset(&mem, 0, sizeof(mem));
> +
>                 r = -EFAULT;
> +               if (get_user(flags, (u32 __user *)(argp + flags_offset)))
> +                       goto out;
> +
> +               if (flags & KVM_MEM_PRIVATE)
> +                       size = sizeof(struct kvm_userspace_memory_region_ext);
> +               else
> +                       size = sizeof(struct kvm_userspace_memory_region);
> +
>                 if (copy_from_user(&mem, argp, size))
>                         goto out;
>
>                 r = -EINVAL;
> -               if (mem.flags & KVM_MEM_PRIVATE)
> +               if ((flags ^ mem.flags) & KVM_MEM_PRIVATE)
>                         goto out;
>
>                 r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> --
> 2.25.1
>

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Chao Peng]

On Fri, Dec 09, 2022 at 08:57:31AM +0000, Fuad Tabba wrote:
> Hi,
> 
> On Thu, Dec 8, 2022 at 11:18 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > On Wed, Dec 07, 2022 at 05:16:34PM +0000, Fuad Tabba wrote:
> > > Hi,
> > >
> > > On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > > >
> > > > Unmap the existing guest mappings when memory attribute is changed
> > > > between shared and private. This is needed because shared pages and
> > > > private pages are from different backends, unmapping existing ones
> > > > gives a chance for page fault handler to re-populate the mappings
> > > > according to the new attribute.
> > > >
> > > > Only architecture has private memory support needs this and the
> > > > supported architecture is expected to rewrite the weak
> > > > kvm_arch_has_private_mem().
> > >
> > > This kind of ties into the discussion of being able to share memory in
> > > place. For pKVM for example, shared and private memory would have the
> > > same backend, and the unmapping wouldn't be needed.
> > >
> > > So I guess that, instead of kvm_arch_has_private_mem(), can the check
> > > be done differently, e.g., with a different function, say
> > > kvm_arch_private_notify_attribute_change() (but maybe with a more
> > > friendly name than what I suggested :) )?
> >
> > Besides controlling the unmapping here, kvm_arch_has_private_mem() is
> > also used to gate the memslot KVM_MEM_PRIVATE flag in patch09. I know
> > unmapping is confirmed unnecessary for pKVM, but how about
> > KVM_MEM_PRIVATE? Will pKVM add its own flag or reuse KVM_MEM_PRIVATE?
> > If the answer is the latter, then yes we should use a different check
> > which only works for confidential usages here.
> 
> I think it makes sense for pKVM to use the same flag (KVM_MEM_PRIVATE)
> and not to add another one.

Thanks for the reply.
Chao
> 
> Thank you,
> /fuad
> 
> 
> 
> >
> > Thanks,
> > Chao
> > >
> > > Thanks,
> > > /fuad
> > >
> > > >
> > > > Also, during memory attribute changing and the unmapping time frame,
> > > > page fault handler may happen in the same memory range and can cause
> > > > incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> > > > page fault handler retry during this time frame.
> > > >
> > > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > > ---
> > > >  include/linux/kvm_host.h |   7 +-
> > > >  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
> > > >  2 files changed, 116 insertions(+), 59 deletions(-)
> > > >
> > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > > index 3d69484d2704..3331c0c92838 100644
> > > > --- a/include/linux/kvm_host.h
> > > > +++ b/include/linux/kvm_host.h
> > > > @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > > >  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> > > >  #endif
> > > >
> > > > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > > >  struct kvm_gfn_range {
> > > >         struct kvm_memory_slot *slot;
> > > >         gfn_t start;
> > > > @@ -264,6 +263,8 @@ struct kvm_gfn_range {
> > > >         bool may_block;
> > > >  };
> > > >  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> > > > +
> > > > +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > > >  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > > >  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > > >  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> > > > @@ -785,11 +786,12 @@ struct kvm {
> > > >
> > > >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> > > >         struct mmu_notifier mmu_notifier;
> > > > +#endif
> > > >         unsigned long mmu_invalidate_seq;
> > > >         long mmu_invalidate_in_progress;
> > > >         gfn_t mmu_invalidate_range_start;
> > > >         gfn_t mmu_invalidate_range_end;
> > > > -#endif
> > > > +
> > > >         struct list_head devices;
> > > >         u64 manual_dirty_log_protect;
> > > >         struct dentry *debugfs_dentry;
> > > > @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> > > >  int kvm_arch_post_init_vm(struct kvm *kvm);
> > > >  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> > > >  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> > > > +bool kvm_arch_has_private_mem(struct kvm *kvm);
> > > >
> > > >  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> > > >  /*
> > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > > index ad55dfbc75d7..4e1e1e113bf0 100644
> > > > --- a/virt/kvm/kvm_main.c
> > > > +++ b/virt/kvm/kvm_main.c
> > > > @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
> > > >
> > > > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > > +{
> > > > +       /*
> > > > +        * The count increase must become visible at unlock time as no
> > > > +        * spte can be established without taking the mmu_lock and
> > > > +        * count is also read inside the mmu_lock critical section.
> > > > +        */
> > > > +       kvm->mmu_invalidate_in_progress++;
> > > > +
> > > > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > > +               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > > +               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > > +       }
> > > > +}
> > > > +
> > > > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > > > +{
> > > > +       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > > +
> > > > +       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > > +               kvm->mmu_invalidate_range_start = start;
> > > > +               kvm->mmu_invalidate_range_end = end;
> > > > +       } else {
> > > > +               /*
> > > > +                * Fully tracking multiple concurrent ranges has diminishing
> > > > +                * returns. Keep things simple and just find the minimal range
> > > > +                * which includes the current and new ranges. As there won't be
> > > > +                * enough information to subtract a range after its invalidate
> > > > +                * completes, any ranges invalidated concurrently will
> > > > +                * accumulate and persist until all outstanding invalidates
> > > > +                * complete.
> > > > +                */
> > > > +               kvm->mmu_invalidate_range_start =
> > > > +                       min(kvm->mmu_invalidate_range_start, start);
> > > > +               kvm->mmu_invalidate_range_end =
> > > > +                       max(kvm->mmu_invalidate_range_end, end);
> > > > +       }
> > > > +}
> > > > +
> > > > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > > +{
> > > > +       /*
> > > > +        * This sequence increase will notify the kvm page fault that
> > > > +        * the page that is going to be mapped in the spte could have
> > > > +        * been freed.
> > > > +        */
> > > > +       kvm->mmu_invalidate_seq++;
> > > > +       smp_wmb();
> > > > +       /*
> > > > +        * The above sequence increase must be visible before the
> > > > +        * below count decrease, which is ensured by the smp_wmb above
> > > > +        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > > > +        */
> > > > +       kvm->mmu_invalidate_in_progress--;
> > > > +}
> > > > +
> > > >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> > > >  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
> > > >  {
> > > > @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> > > >         kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> > > >  }
> > > >
> > > > -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > > -{
> > > > -       /*
> > > > -        * The count increase must become visible at unlock time as no
> > > > -        * spte can be established without taking the mmu_lock and
> > > > -        * count is also read inside the mmu_lock critical section.
> > > > -        */
> > > > -       kvm->mmu_invalidate_in_progress++;
> > > > -
> > > > -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > > -               kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > > -               kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > > -       }
> > > > -}
> > > > -
> > > > -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > > > -{
> > > > -       WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > > -
> > > > -       if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > > -               kvm->mmu_invalidate_range_start = start;
> > > > -               kvm->mmu_invalidate_range_end = end;
> > > > -       } else {
> > > > -               /*
> > > > -                * Fully tracking multiple concurrent ranges has diminishing
> > > > -                * returns. Keep things simple and just find the minimal range
> > > > -                * which includes the current and new ranges. As there won't be
> > > > -                * enough information to subtract a range after its invalidate
> > > > -                * completes, any ranges invalidated concurrently will
> > > > -                * accumulate and persist until all outstanding invalidates
> > > > -                * complete.
> > > > -                */
> > > > -               kvm->mmu_invalidate_range_start =
> > > > -                       min(kvm->mmu_invalidate_range_start, start);
> > > > -               kvm->mmu_invalidate_range_end =
> > > > -                       max(kvm->mmu_invalidate_range_end, end);
> > > > -       }
> > > > -}
> > > > -
> > > >  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> > > >  {
> > > >         kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > > > @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> > > >         return 0;
> > > >  }
> > > >
> > > > -void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > > -{
> > > > -       /*
> > > > -        * This sequence increase will notify the kvm page fault that
> > > > -        * the page that is going to be mapped in the spte could have
> > > > -        * been freed.
> > > > -        */
> > > > -       kvm->mmu_invalidate_seq++;
> > > > -       smp_wmb();
> > > > -       /*
> > > > -        * The above sequence increase must be visible before the
> > > > -        * below count decrease, which is ensured by the smp_wmb above
> > > > -        * in conjunction with the smp_rmb in mmu_invalidate_retry().
> > > > -        */
> > > > -       kvm->mmu_invalidate_in_progress--;
> > > > -}
> > > > -
> > > >  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> > > >                                         const struct mmu_notifier_range *range)
> > > >  {
> > > > @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
> > > >         return 0;
> > > >  }
> > > >
> > > > +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> > > > +{
> > > > +       return false;
> > > > +}
> > > > +
> > > >  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> > > >  {
> > > >         struct kvm *kvm = kvm_arch_alloc_vm();
> > > > @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> > > >         return 0;
> > > >  }
> > > >
> > > > +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> > > > +{
> > > > +       struct kvm_gfn_range gfn_range;
> > > > +       struct kvm_memory_slot *slot;
> > > > +       struct kvm_memslots *slots;
> > > > +       struct kvm_memslot_iter iter;
> > > > +       int i;
> > > > +       int r = 0;
> > > > +
> > > > +       gfn_range.pte = __pte(0);
> > > > +       gfn_range.may_block = true;
> > > > +
> > > > +       for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > > > +               slots = __kvm_memslots(kvm, i);
> > > > +
> > > > +               kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> > > > +                       slot = iter.slot;
> > > > +                       gfn_range.start = max(start, slot->base_gfn);
> > > > +                       gfn_range.end = min(end, slot->base_gfn + slot->npages);
> > > > +                       if (gfn_range.start >= gfn_range.end)
> > > > +                               continue;
> > > > +                       gfn_range.slot = slot;
> > > > +
> > > > +                       r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> > > > +               }
> > > > +       }
> > > > +
> > > > +       if (r)
> > > > +               kvm_flush_remote_tlbs(kvm);
> > > > +}
> > > > +
> > > >  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > > >                                            struct kvm_memory_attributes *attrs)
> > > >  {
> > > >         gfn_t start, end;
> > > >         unsigned long i;
> > > >         void *entry;
> > > > +       int idx;
> > > >         u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > > >
> > > > -       /* flags is currently not used. */
> > > > +       /* 'flags' is currently not used. */
> > > >         if (attrs->flags)
> > > >                 return -EINVAL;
> > > >         if (attrs->attributes & ~supported_attrs)
> > > > @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > > >
> > > >         entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > > >
> > > > +       if (kvm_arch_has_private_mem(kvm)) {
> > > > +               KVM_MMU_LOCK(kvm);
> > > > +               kvm_mmu_invalidate_begin(kvm);
> > > > +               kvm_mmu_invalidate_range_add(kvm, start, end);
> > > > +               KVM_MMU_UNLOCK(kvm);
> > > > +       }
> > > > +
> > > >         mutex_lock(&kvm->lock);
> > > >         for (i = start; i < end; i++)
> > > >                 if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > > > @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > > >                         break;
> > > >         mutex_unlock(&kvm->lock);
> > > >
> > > > +       if (kvm_arch_has_private_mem(kvm)) {
> > > > +               idx = srcu_read_lock(&kvm->srcu);
> > > > +               KVM_MMU_LOCK(kvm);
> > > > +               if (i > start)
> > > > +                       kvm_unmap_mem_range(kvm, start, i);
> > > > +               kvm_mmu_invalidate_end(kvm);
> > > > +               KVM_MMU_UNLOCK(kvm);
> > > > +               srcu_read_unlock(&kvm->srcu, idx);
> > > > +       }
> > > > +
> > > >         attrs->address = i << PAGE_SHIFT;
> > > >         attrs->size = (end - i) << PAGE_SHIFT;
> > > >
> > > > --
> > > > 2.25.1
> > > >

Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

[Chao Peng]

On Fri, Dec 09, 2022 at 09:01:04AM +0000, Fuad Tabba wrote:
> Hi,
> 
> On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > A KVM_MEM_PRIVATE memslot can include both fd-based private memory and
> > hva-based shared memory. Architecture code (like TDX code) can tell
> > whether the on-going fault is private or not. This patch adds a
> > 'is_private' field to kvm_page_fault to indicate this and architecture
> > code is expected to set it.
> >
> > To handle page fault for such memslot, the handling logic is different
> > depending on whether the fault is private or shared. KVM checks if
> > 'is_private' matches the host's view of the page (maintained in
> > mem_attr_array).
> >   - For a successful match, private pfn is obtained with
> >     restrictedmem_get_page() and shared pfn is obtained with existing
> >     get_user_pages().
> >   - For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
> >     userspace. Userspace then can convert memory between private/shared
> >     in host's view and retry the fault.
> >
> > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++++++++++++++--
> >  arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
> >  arch/x86/kvm/mmu/mmutrace.h     |  1 +
> >  arch/x86/kvm/mmu/tdp_mmu.c      |  2 +-
> >  include/linux/kvm_host.h        | 30 ++++++++++++++++
> >  5 files changed, 105 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 2190fd8c95c0..b1953ebc012e 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3058,7 +3058,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
> >
> >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> >                               const struct kvm_memory_slot *slot, gfn_t gfn,
> > -                             int max_level)
> > +                             int max_level, bool is_private)
> >  {
> >         struct kvm_lpage_info *linfo;
> >         int host_level;
> > @@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> >                         break;
> >         }
> >
> > +       if (is_private)
> > +               return max_level;
> > +
> >         if (max_level == PG_LEVEL_4K)
> >                 return PG_LEVEL_4K;
> >
> > @@ -3098,7 +3101,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> >          * level, which will be used to do precise, accurate accounting.
> >          */
> >         fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> > -                                                    fault->gfn, fault->max_level);
> > +                                                    fault->gfn, fault->max_level,
> > +                                                    fault->is_private);
> >         if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
> >                 return;
> >
> > @@ -4178,6 +4182,49 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> >         kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
> >  }
> >
> > +static inline u8 order_to_level(int order)
> > +{
> > +       BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> > +
> > +       if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> > +               return PG_LEVEL_1G;
> > +
> > +       if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> > +               return PG_LEVEL_2M;
> > +
> > +       return PG_LEVEL_4K;
> > +}
> > +
> > +static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> > +                                   struct kvm_page_fault *fault)
> > +{
> > +       vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> > +       if (fault->is_private)
> > +               vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> > +       else
> > +               vcpu->run->memory.flags = 0;
> > +       vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> 
> nit: As in previous patches, use helpers (for this and other similar
> shifts in this patch)?

Agreed.

> 
> > +       vcpu->run->memory.size = PAGE_SIZE;
> > +       return RET_PF_USER;
> > +}
> > +
> > +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> > +                                  struct kvm_page_fault *fault)
> > +{
> > +       int order;
> > +       struct kvm_memory_slot *slot = fault->slot;
> > +
> > +       if (!kvm_slot_can_be_private(slot))
> > +               return kvm_do_memory_fault_exit(vcpu, fault);
> > +
> > +       if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> > +               return RET_PF_RETRY;
> > +
> > +       fault->max_level = min(order_to_level(order), fault->max_level);
> > +       fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
> > +       return RET_PF_CONTINUE;
> > +}
> > +
> >  static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >  {
> >         struct kvm_memory_slot *slot = fault->slot;
> > @@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >                         return RET_PF_EMULATE;
> >         }
> >
> > +       if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> > +               return kvm_do_memory_fault_exit(vcpu, fault);
> > +
> > +       if (fault->is_private)
> > +               return kvm_faultin_pfn_private(vcpu, fault);
> > +
> >         async = false;
> >         fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
> >                                           fault->write, &fault->map_writable,
> > @@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
> >                         return -EIO;
> >         }
> >
> > +       if (r == RET_PF_USER)
> > +               return 0;
> > +
> >         if (r < 0)
> >                 return r;
> >         if (r != RET_PF_EMULATE)
> > @@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> >                  */
> >                 if (sp->role.direct &&
> >                     sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> > -                                                              PG_LEVEL_NUM)) {
> > +                                                              PG_LEVEL_NUM,
> > +                                                              false)) {
> >                         kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
> >
> >                         if (kvm_available_flush_tlb_with_range())
> > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> > index dbaf6755c5a7..5ccf08183b00 100644
> > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > @@ -189,6 +189,7 @@ struct kvm_page_fault {
> >
> >         /* Derived from mmu and global state.  */
> >         const bool is_tdp;
> > +       const bool is_private;
> >         const bool nx_huge_page_workaround_enabled;
> >
> >         /*
> > @@ -237,6 +238,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> >   * RET_PF_RETRY: let CPU fault again on the address.
> >   * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
> >   * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
> > + * RET_PF_USER: need to exit to userspace to handle this fault.
> >   * RET_PF_FIXED: The faulting entry has been fixed.
> >   * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
> >   *
> > @@ -253,6 +255,7 @@ enum {
> >         RET_PF_RETRY,
> >         RET_PF_EMULATE,
> >         RET_PF_INVALID,
> > +       RET_PF_USER,
> >         RET_PF_FIXED,
> >         RET_PF_SPURIOUS,
> >  };
> > @@ -310,7 +313,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> >
> >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> >                               const struct kvm_memory_slot *slot, gfn_t gfn,
> > -                             int max_level);
> > +                             int max_level, bool is_private);
> >  void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> >  void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
> >
> > @@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> >  void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> >  void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> >
> > +#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > +                                       gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > +{
> > +       WARN_ON_ONCE(1);
> > +       return -EOPNOTSUPP;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > +
> >  #endif /* __KVM_X86_MMU_INTERNAL_H */
> > diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> > index ae86820cef69..2d7555381955 100644
> > --- a/arch/x86/kvm/mmu/mmutrace.h
> > +++ b/arch/x86/kvm/mmu/mmutrace.h
> > @@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
> >  TRACE_DEFINE_ENUM(RET_PF_RETRY);
> >  TRACE_DEFINE_ENUM(RET_PF_EMULATE);
> >  TRACE_DEFINE_ENUM(RET_PF_INVALID);
> > +TRACE_DEFINE_ENUM(RET_PF_USER);
> >  TRACE_DEFINE_ENUM(RET_PF_FIXED);
> >  TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
> >
> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index 771210ce5181..8ba1a4afc546 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -1768,7 +1768,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
> >                         continue;
> >
> >                 max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
> > -                                                             iter.gfn, PG_LEVEL_NUM);
> > +                                               iter.gfn, PG_LEVEL_NUM, false);
> >                 if (max_mapping_level < iter.level)
> >                         continue;
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 25099c94e770..153842bb33df 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> >  }
> >  #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
> >
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > +{
> > +       return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> > +              KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > +}
> > +#else
> > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > +{
> > +       return false;
> > +}
> > +
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > +
> > +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > +                                       gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > +{
> > +       int ret;
> > +       struct page *page;
> > +       pgoff_t index = gfn - slot->base_gfn +
> > +                       (slot->restricted_offset >> PAGE_SHIFT);
> > +
> > +       ret = restrictedmem_get_page(slot->restricted_file, index,
> > +                                    &page, order);
> > +       *pfn = page_to_pfn(page);
> > +       return ret;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > +
> >  #endif
> > --
> > 2.25.1
> >
> 
> With my limited understanding of x86 code:
> Reviewed-by: Fuad Tabba <tabba@google.com>
> 
> The common code in kvm_host.h was used in the port to arm64, and the
> x86 fault handling code was used as a guide to how it should be done
> in pKVM (with similar code added there). So with these caveats in
> mind:
> Tested-by: Fuad Tabba <tabba@google.com>
> 
> Cheers,
> /fuad

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Xiaoyao Li]

On 12/8/2022 7:30 PM, Chao Peng wrote:
> On Thu, Dec 08, 2022 at 04:37:03PM +0800, Xiaoyao Li wrote:
>> On 12/2/2022 2:13 PM, Chao Peng wrote:
>>
>> ..
>>
>>> Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
>>> and right now it is selected on X86_64 only.
>>>
>>
>>  From the patch implementation, I have no idea why HAVE_KVM_RESTRICTED_MEM is
>> needed.
> 
> The reason is we want KVM further controls the feature enabling. An
> opt-in CONFIG_RESTRICTEDMEM can cause problem if user sets that for
> unsupported architectures.

HAVE_KVM_RESTRICTED_MEM is not used in this patch. It's better to 
introduce it in the patch that actually uses it.

> Here is the original discussion:
> https://lore.kernel.org/all/YkJLFu98hZOvTSrL@google.com/
> 
> Thanks,
> Chao

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Huang, Kai]

> 
> memfd_restricted() itself is implemented as a shim layer on top of real
> memory file systems (currently tmpfs). Pages in restrictedmem are marked
> as unmovable and unevictable, this is required for current confidential
> usage. But in future this might be changed.
> 
> 
I didn't dig full histroy, but I interpret this as we don't support page
migration and swapping for restricted memfd for now.  IMHO "page marked as
unmovable" can be confused with PageMovable(), which is a different thing from
this series.  It's better to just say something like "those pages cannot be
migrated and swapped".

[...]

> +
> +	/*
> +	 * These pages are currently unmovable so don't place them into movable
> +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> +	 */
> +	mapping = memfd->f_mapping;
> +	mapping_set_unevictable(mapping);
> +	mapping_set_gfp_mask(mapping,
> +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);

But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from non-
movable zones, but doesn't necessarily prevent page from being migrated.  My
first glance is you need to implement either a_ops->migrate_folio() or just
get_page() after faulting in the page to prevent.

So I think the comment also needs improvement -- IMHO we can just call out
currently those pages cannot be migrated and swapped, which is clearer (and the
latter justifies mapping_set_unevictable() clearly).

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Huang, Kai]

On Fri, 2022-12-02 at 14:13 +0800, Chao Peng wrote:
>  
> -	/* flags is currently not used. */
> +	/* 'flags' is currently not used. */
>  	if (attrs->flags)
>  		return -EINVAL;

Unintended code change.

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Borislav Petkov]

On Fri, Dec 02, 2022 at 02:13:40PM +0800, Chao Peng wrote:
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1782c4555d94..7f0f5e9f2406 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>  	spin_lock_init(&kvm->mn_invalidate_lock);
>  	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
>  	xa_init(&kvm->vcpu_array);
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	xa_init(&kvm->mem_attr_array);
> +#endif

	if (IS_ENABLED(CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES))
		...

would at least remove the ugly ifdeffery.

Or you could create wrapper functions for that xa_init() and
xa_destroy() and put the ifdeffery in there.

> @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
>  }
>  #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
>  
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +static u64 kvm_supported_mem_attributes(struct kvm *kvm)

I guess that function should have a verb in the name:

kvm_get_supported_mem_attributes()

> +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> +					   struct kvm_memory_attributes *attrs)
> +{
> +	gfn_t start, end;
> +	unsigned long i;
> +	void *entry;
> +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> +
> +	/* flags is currently not used. */
> +	if (attrs->flags)
> +		return -EINVAL;
> +	if (attrs->attributes & ~supported_attrs)
> +		return -EINVAL;
> +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> +		return -EINVAL;
> +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> +		return -EINVAL;

Dunno, shouldn't those issue some sort of an error message so that the
caller knows where it failed? Or at least return different retvals which
signal what the problem is?

> +	start = attrs->address >> PAGE_SHIFT;
> +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> +
> +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> +
> +	mutex_lock(&kvm->lock);
> +	for (i = start; i < end; i++)
> +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> +				    GFP_KERNEL_ACCOUNT)))
> +			break;
> +	mutex_unlock(&kvm->lock);
> +
> +	attrs->address = i << PAGE_SHIFT;
> +	attrs->size = (end - i) << PAGE_SHIFT;
> +
> +	return 0;
> +}

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Tue, Dec 13, 2022 at 08:04:14PM +0800, Xiaoyao Li wrote:
> On 12/8/2022 7:30 PM, Chao Peng wrote:
> > On Thu, Dec 08, 2022 at 04:37:03PM +0800, Xiaoyao Li wrote:
> > > On 12/2/2022 2:13 PM, Chao Peng wrote:
> > > 
> > > ..
> > > 
> > > > Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> > > > and right now it is selected on X86_64 only.
> > > > 
> > > 
> > >  From the patch implementation, I have no idea why HAVE_KVM_RESTRICTED_MEM is
> > > needed.
> > 
> > The reason is we want KVM further controls the feature enabling. An
> > opt-in CONFIG_RESTRICTEDMEM can cause problem if user sets that for
> > unsupported architectures.
> 
> HAVE_KVM_RESTRICTED_MEM is not used in this patch. It's better to introduce
> it in the patch that actually uses it.

It's being 'used' in this patch by reverse selecting RESTRICTEDMEM in
arch/x86/kvm/Kconfig, this gives people a sense where
restrictedmem_notifier comes from. Introducing the config with other
private/restricted memslot stuff together can also help future
supporting architectures better identify what they need do. But those
are trivial and moving to patch 08 sounds also good to me.

Thanks,
Chao
> 
> > Here is the original discussion:
> > https://lore.kernel.org/all/YkJLFu98hZOvTSrL@google.com/
> > 
> > Thanks,
> > Chao

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Tue, Dec 13, 2022 at 11:49:13PM +0000, Huang, Kai wrote:
> > 
> > memfd_restricted() itself is implemented as a shim layer on top of real
> > memory file systems (currently tmpfs). Pages in restrictedmem are marked
> > as unmovable and unevictable, this is required for current confidential
> > usage. But in future this might be changed.
> > 
> > 
> I didn't dig full histroy, but I interpret this as we don't support page
> migration and swapping for restricted memfd for now.  IMHO "page marked as
> unmovable" can be confused with PageMovable(), which is a different thing from
> this series.  It's better to just say something like "those pages cannot be
> migrated and swapped".

Yes, if that helps some clarification.

> 
> [...]
> 
> > +
> > +	/*
> > +	 * These pages are currently unmovable so don't place them into movable
> > +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > +	 */
> > +	mapping = memfd->f_mapping;
> > +	mapping_set_unevictable(mapping);
> > +	mapping_set_gfp_mask(mapping,
> > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> 
> But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from non-
> movable zones, but doesn't necessarily prevent page from being migrated.  My
> first glance is you need to implement either a_ops->migrate_folio() or just
> get_page() after faulting in the page to prevent.

The current api restrictedmem_get_page() already does this, after the
caller calling it, it holds a reference to the page. The caller then
decides when to call put_page() appropriately.

> 
> So I think the comment also needs improvement -- IMHO we can just call out
> currently those pages cannot be migrated and swapped, which is clearer (and the
> latter justifies mapping_set_unevictable() clearly).

Good to me.

Thanks,
Chao
> 
> 

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Chao Peng]

On Tue, Dec 13, 2022 at 11:51:25PM +0000, Huang, Kai wrote:
> On Fri, 2022-12-02 at 14:13 +0800, Chao Peng wrote:
> >  
> > -	/* flags is currently not used. */
> > +	/* 'flags' is currently not used. */
> >  	if (attrs->flags)
> >  		return -EINVAL;
> 
> Unintended code change.

Yeah!

Chao

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Fri, Dec 16, 2022 at 04:09:06PM +0100, Borislav Petkov wrote:
> On Fri, Dec 02, 2022 at 02:13:40PM +0800, Chao Peng wrote:
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 1782c4555d94..7f0f5e9f2406 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> >  	spin_lock_init(&kvm->mn_invalidate_lock);
> >  	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
> >  	xa_init(&kvm->vcpu_array);
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +	xa_init(&kvm->mem_attr_array);
> > +#endif
> 
> 	if (IS_ENABLED(CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES))
> 		...
> 
> would at least remove the ugly ifdeffery.
> 
> Or you could create wrapper functions for that xa_init() and
> xa_destroy() and put the ifdeffery in there.

Agreed.

> 
> > @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
> >  }
> >  #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
> >  
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> 
> I guess that function should have a verb in the name:
> 
> kvm_get_supported_mem_attributes()

Right!
> 
> > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > +					   struct kvm_memory_attributes *attrs)
> > +{
> > +	gfn_t start, end;
> > +	unsigned long i;
> > +	void *entry;
> > +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +	/* flags is currently not used. */
> > +	if (attrs->flags)
> > +		return -EINVAL;
> > +	if (attrs->attributes & ~supported_attrs)
> > +		return -EINVAL;
> > +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > +		return -EINVAL;
> > +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > +		return -EINVAL;
> 
> Dunno, shouldn't those issue some sort of an error message so that the
> caller knows where it failed? Or at least return different retvals which
> signal what the problem is?

Tamping down with error number a bit:

        if (attrs->flags)
                return -ENXIO;
        if (attrs->attributes & ~supported_attrs)
                return -EOPNOTSUPP;
        if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size) ||
            attrs->size == 0)
                return -EINVAL;
        if (attrs->address + attrs->size < attrs->address)
                return -E2BIG;

Chao
> 
> > +	start = attrs->address >> PAGE_SHIFT;
> > +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> > +
> > +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > +
> > +	mutex_lock(&kvm->lock);
> > +	for (i = start; i < end; i++)
> > +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > +				    GFP_KERNEL_ACCOUNT)))
> > +			break;
> > +	mutex_unlock(&kvm->lock);
> > +
> > +	attrs->address = i << PAGE_SHIFT;
> > +	attrs->size = (end - i) << PAGE_SHIFT;
> > +
> > +	return 0;
> > +}
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Huang, Kai]

On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > 
> > [...]
> > 
> > > +
> > > +	/*
> > > +	 * These pages are currently unmovable so don't place them into
> > > movable
> > > +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > > +	 */
> > > +	mapping = memfd->f_mapping;
> > > +	mapping_set_unevictable(mapping);
> > > +	mapping_set_gfp_mask(mapping,
> > > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > 
> > But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from
> > non-
> > movable zones, but doesn't necessarily prevent page from being migrated.  My
> > first glance is you need to implement either a_ops->migrate_folio() or just
> > get_page() after faulting in the page to prevent.
> 
> The current api restrictedmem_get_page() already does this, after the
> caller calling it, it holds a reference to the page. The caller then
> decides when to call put_page() appropriately.

I tried to dig some history. Perhaps I am missing something, but it seems Kirill
said in v9 that this code doesn't prevent page migration, and we need to
increase page refcount in restrictedmem_get_page():

https://lore.kernel.org/linux-mm/20221129112139.usp6dqhbih47qpjl@box.shutemov.name/

But looking at this series it seems restrictedmem_get_page() in this v10 is
identical to the one in v9 (except v10 uses 'folio' instead of 'page')?

Anyway if this is not fixed, then it should be fixed.  Otherwise, a comment at
the place where page refcount is increased will be helpful to help people
understand page migration is actually prevented.

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Borislav Petkov]

On Mon, Dec 19, 2022 at 04:15:32PM +0800, Chao Peng wrote:
> Tamping down with error number a bit:
> 
>         if (attrs->flags)
>                 return -ENXIO;
>         if (attrs->attributes & ~supported_attrs)
>                 return -EOPNOTSUPP;
>         if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size) ||
>             attrs->size == 0)
>                 return -EINVAL;
>         if (attrs->address + attrs->size < attrs->address)
>                 return -E2BIG;

Yap, better.

I guess you should add those to the documentation of the ioctl too
so that people can find out why it fails. Or, well, they can look
at the code directly too but still... imagine some blurb about
user-friendliness here...

:-)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Borislav Petkov]

On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> In memory encryption usage, guest memory may be encrypted with special
> key and can be accessed only by the guest itself. We call such memory
> private memory. It's valueless and sometimes can cause problem to allow

valueless?

I can't parse that.

> userspace to access guest private memory. This new KVM memslot extension
> allows guest private memory being provided through a restrictedmem
> backed file descriptor(fd) and userspace is restricted to access the
> bookmarked memory in the fd.

bookmarked?

> This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> additional KVM memslot fields restricted_fd/restricted_offset to allow
> userspace to instruct KVM to provide guest memory through restricted_fd.
> 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> and the size is 'memory_size'.
> 
> The extended memslot can still have the userspace_addr(hva). When use, a

"When un use, ..."

...

> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index a8e379a3afee..690cb21010e7 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -50,6 +50,8 @@ config KVM
>  	select INTERVAL_TREE
>  	select HAVE_KVM_PM_NOTIFIER if PM
>  	select HAVE_KVM_MEMORY_ATTRIBUTES
> +	select HAVE_KVM_RESTRICTED_MEM if X86_64
> +	select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM

Those deps here look weird.

RESTRICTEDMEM should be selected by TDX_GUEST as it can't live without
it.

Then you don't have to select HAVE_KVM_RESTRICTED_MEM simply because of
X86_64 - you need that functionality when the respective guest support
is enabled in KVM.

Then, looking forward into your patchset, I'm not sure you even
need HAVE_KVM_RESTRICTED_MEM - you could make it all depend on
CONFIG_RESTRICTEDMEM. But that's KVM folks call - I'd always aim for
less Kconfig items because we have waay too many.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > 
> > > [...]
> > > 
> > > > +
> > > > +	/*
> > > > +	 * These pages are currently unmovable so don't place them into
> > > > movable
> > > > +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > > > +	 */
> > > > +	mapping = memfd->f_mapping;
> > > > +	mapping_set_unevictable(mapping);
> > > > +	mapping_set_gfp_mask(mapping,
> > > > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > > 
> > > But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from
> > > non-
> > > movable zones, but doesn't necessarily prevent page from being migrated.  My
> > > first glance is you need to implement either a_ops->migrate_folio() or just
> > > get_page() after faulting in the page to prevent.
> > 
> > The current api restrictedmem_get_page() already does this, after the
> > caller calling it, it holds a reference to the page. The caller then
> > decides when to call put_page() appropriately.
> 
> I tried to dig some history. Perhaps I am missing something, but it seems Kirill
> said in v9 that this code doesn't prevent page migration, and we need to
> increase page refcount in restrictedmem_get_page():
> 
> https://lore.kernel.org/linux-mm/20221129112139.usp6dqhbih47qpjl@box.shutemov.name/
> 
> But looking at this series it seems restrictedmem_get_page() in this v10 is
> identical to the one in v9 (except v10 uses 'folio' instead of 'page')?

restrictedmem_get_page() increases page refcount several versions ago so
no change in v10 is needed. You probably missed my reply:

https://lore.kernel.org/linux-mm/20221129135844.GA902164@chaop.bj.intel.com/

The current solution is clear: unless we have better approach, we will
let restrictedmem user (KVM in this case) to hold the refcount to
prevent page migration.

Thanks,
Chao
> 
> Anyway if this is not fixed, then it should be fixed.  Otherwise, a comment at
> the place where page refcount is increased will be helpful to help people
> understand page migration is actually prevented.
> 

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Mon, Dec 19, 2022 at 11:17:22AM +0100, Borislav Petkov wrote:
> On Mon, Dec 19, 2022 at 04:15:32PM +0800, Chao Peng wrote:
> > Tamping down with error number a bit:
> > 
> >         if (attrs->flags)
> >                 return -ENXIO;
> >         if (attrs->attributes & ~supported_attrs)
> >                 return -EOPNOTSUPP;
> >         if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size) ||
> >             attrs->size == 0)
> >                 return -EINVAL;
> >         if (attrs->address + attrs->size < attrs->address)
> >                 return -E2BIG;
> 
> Yap, better.
> 
> I guess you should add those to the documentation of the ioctl too
> so that people can find out why it fails. Or, well, they can look
> at the code directly too but still... imagine some blurb about
> user-friendliness here...

Thanks for reminding. Yes KVM api doc is the right place to put these
documentation in.

Thanks,
Chao
> 
> :-)
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Mon, Dec 19, 2022 at 03:36:28PM +0100, Borislav Petkov wrote:
> On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > In memory encryption usage, guest memory may be encrypted with special
> > key and can be accessed only by the guest itself. We call such memory
> > private memory. It's valueless and sometimes can cause problem to allow
> 
> valueless?
> 
> I can't parse that.

It's unnecessary and ...

> 
> > userspace to access guest private memory. This new KVM memslot extension
> > allows guest private memory being provided through a restrictedmem
> > backed file descriptor(fd) and userspace is restricted to access the
> > bookmarked memory in the fd.
> 
> bookmarked?

userspace is restricted to access the memory content in the fd.

> 
> > This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> > additional KVM memslot fields restricted_fd/restricted_offset to allow
> > userspace to instruct KVM to provide guest memory through restricted_fd.
> > 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> > and the size is 'memory_size'.
> > 
> > The extended memslot can still have the userspace_addr(hva). When use, a
> 
> "When un use, ..."

When both userspace_addr and restricted_fd/offset were used, ...

> 
> ...
> 
> > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > index a8e379a3afee..690cb21010e7 100644
> > --- a/arch/x86/kvm/Kconfig
> > +++ b/arch/x86/kvm/Kconfig
> > @@ -50,6 +50,8 @@ config KVM
> >  	select INTERVAL_TREE
> >  	select HAVE_KVM_PM_NOTIFIER if PM
> >  	select HAVE_KVM_MEMORY_ATTRIBUTES
> > +	select HAVE_KVM_RESTRICTED_MEM if X86_64
> > +	select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
> 
> Those deps here look weird.
> 
> RESTRICTEDMEM should be selected by TDX_GUEST as it can't live without
> it.

RESTRICTEDMEM is needed by TDX_HOST, not TDX_GUEST.

> 
> Then you don't have to select HAVE_KVM_RESTRICTED_MEM simply because of
> X86_64 - you need that functionality when the respective guest support
> is enabled in KVM.

Letting the actual feature(e.g. TDX or pKVM) select it or add dependency
sounds a viable and clearer solution. Sean, let me know your opinion.

> 
> Then, looking forward into your patchset, I'm not sure you even
> need HAVE_KVM_RESTRICTED_MEM - you could make it all depend on
> CONFIG_RESTRICTEDMEM. But that's KVM folks call - I'd always aim for
> less Kconfig items because we have waay too many.

The only reason to add another HAVE_KVM_RESTRICTED_MEM is some code only
works for 64bit[*] and CONFIG_RESTRICTEDMEM is not sufficient to enforce
that.

[*] https://lore.kernel.org/all/YkJLFu98hZOvTSrL@google.com/

Thanks,
Chao
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Huang, Kai]

On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > > 
> > > > [...]
> > > > 
> > > > > +
> > > > > +	/*
> > > > > +	 * These pages are currently unmovable so don't place them into
> > > > > movable
> > > > > +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > > > > +	 */
> > > > > +	mapping = memfd->f_mapping;
> > > > > +	mapping_set_unevictable(mapping);
> > > > > +	mapping_set_gfp_mask(mapping,
> > > > > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > > > 
> > > > But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from
> > > > non-
> > > > movable zones, but doesn't necessarily prevent page from being migrated.  My
> > > > first glance is you need to implement either a_ops->migrate_folio() or just
> > > > get_page() after faulting in the page to prevent.
> > > 
> > > The current api restrictedmem_get_page() already does this, after the
> > > caller calling it, it holds a reference to the page. The caller then
> > > decides when to call put_page() appropriately.
> > 
> > I tried to dig some history. Perhaps I am missing something, but it seems Kirill
> > said in v9 that this code doesn't prevent page migration, and we need to
> > increase page refcount in restrictedmem_get_page():
> > 
> > https://lore.kernel.org/linux-mm/20221129112139.usp6dqhbih47qpjl@box.shutemov.name/
> > 
> > But looking at this series it seems restrictedmem_get_page() in this v10 is
> > identical to the one in v9 (except v10 uses 'folio' instead of 'page')?
> 
> restrictedmem_get_page() increases page refcount several versions ago so
> no change in v10 is needed. You probably missed my reply:
> 
> https://lore.kernel.org/linux-mm/20221129135844.GA902164@chaop.bj.intel.com/

But for non-restricted-mem case, it is correct for KVM to decrease page's
refcount after setting up mapping in the secondary mmu, otherwise the page will
be pinned by KVM for normal VM (since KVM uses GUP to get the page).

So what we are expecting is: for KVM if the page comes from restricted mem, then
KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.

> 
> The current solution is clear: unless we have better approach, we will
> let restrictedmem user (KVM in this case) to hold the refcount to
> prevent page migration.
> 

OK.  Will leave to others :)

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Borislav Petkov]

On Tue, Dec 20, 2022 at 03:43:18PM +0800, Chao Peng wrote:
> RESTRICTEDMEM is needed by TDX_HOST, not TDX_GUEST.

Which basically means that RESTRICTEDMEM should simply depend on KVM.
Because you can't know upfront whether KVM will run a TDX guest or a SNP
guest and so on.

Which then means that RESTRICTEDMEM will practically end up always
enabled in KVM HV configs.

> The only reason to add another HAVE_KVM_RESTRICTED_MEM is some code only
> works for 64bit[*] and CONFIG_RESTRICTEDMEM is not sufficient to enforce
> that.

This is what I mean with "we have too many Kconfig items". :-\

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > > > 
> > > > > [...]
> > > > > 
> > > > > > +
> > > > > > +	/*
> > > > > > +	 * These pages are currently unmovable so don't place them into
> > > > > > movable
> > > > > > +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > > > > > +	 */
> > > > > > +	mapping = memfd->f_mapping;
> > > > > > +	mapping_set_unevictable(mapping);
> > > > > > +	mapping_set_gfp_mask(mapping,
> > > > > > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > > > > 
> > > > > But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from
> > > > > non-
> > > > > movable zones, but doesn't necessarily prevent page from being migrated.  My
> > > > > first glance is you need to implement either a_ops->migrate_folio() or just
> > > > > get_page() after faulting in the page to prevent.
> > > > 
> > > > The current api restrictedmem_get_page() already does this, after the
> > > > caller calling it, it holds a reference to the page. The caller then
> > > > decides when to call put_page() appropriately.
> > > 
> > > I tried to dig some history. Perhaps I am missing something, but it seems Kirill
> > > said in v9 that this code doesn't prevent page migration, and we need to
> > > increase page refcount in restrictedmem_get_page():
> > > 
> > > https://lore.kernel.org/linux-mm/20221129112139.usp6dqhbih47qpjl@box.shutemov.name/
> > > 
> > > But looking at this series it seems restrictedmem_get_page() in this v10 is
> > > identical to the one in v9 (except v10 uses 'folio' instead of 'page')?
> > 
> > restrictedmem_get_page() increases page refcount several versions ago so
> > no change in v10 is needed. You probably missed my reply:
> > 
> > https://lore.kernel.org/linux-mm/20221129135844.GA902164@chaop.bj.intel.com/
> 
> But for non-restricted-mem case, it is correct for KVM to decrease page's
> refcount after setting up mapping in the secondary mmu, otherwise the page will
> be pinned by KVM for normal VM (since KVM uses GUP to get the page).

That's true. Actually even true for restrictedmem case, most likely we
will still need the kvm_release_pfn_clean() for KVM generic code. On one
side, other restrictedmem users like pKVM may not require page pinning
at all. On the other side, see below.

> 
> So what we are expecting is: for KVM if the page comes from restricted mem, then
> KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.

I argue that this page pinning (or page migration prevention) is not
tied to where the page comes from, instead related to how the page will
be used. Whether the page is restrictedmem backed or GUP() backed, once
it's used by current version of TDX then the page pinning is needed. So
such page migration prevention is really TDX thing, even not KVM generic
thing (that's why I think we don't need change the existing logic of
kvm_release_pfn_clean()). Wouldn't better to let TDX code (or who
requires that) to increase/decrease the refcount when it populates/drops
the secure EPT entries? This is exactly what the current TDX code does:

get_page():
https://github.com/intel/tdx/blob/kvm-upstream/arch/x86/kvm/vmx/tdx.c#L1217

put_page():
https://github.com/intel/tdx/blob/kvm-upstream/arch/x86/kvm/vmx/tdx.c#L1334

Thanks,
Chao
> 
> > 
> > The current solution is clear: unless we have better approach, we will
> > let restrictedmem user (KVM in this case) to hold the refcount to
> > prevent page migration.
> > 
> 
> OK.  Will leave to others :)
> 

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Tue, Dec 20, 2022 at 10:55:44AM +0100, Borislav Petkov wrote:
> On Tue, Dec 20, 2022 at 03:43:18PM +0800, Chao Peng wrote:
> > RESTRICTEDMEM is needed by TDX_HOST, not TDX_GUEST.
> 
> Which basically means that RESTRICTEDMEM should simply depend on KVM.
> Because you can't know upfront whether KVM will run a TDX guest or a SNP
> guest and so on.
> 
> Which then means that RESTRICTEDMEM will practically end up always
> enabled in KVM HV configs.

That's right, CONFIG_RESTRICTEDMEM is always selected for supported KVM
architectures (currently x86_64).

> 
> > The only reason to add another HAVE_KVM_RESTRICTED_MEM is some code only
> > works for 64bit[*] and CONFIG_RESTRICTEDMEM is not sufficient to enforce
> > that.
> 
> This is what I mean with "we have too many Kconfig items". :-\

Yes I agree. One way to remove this is probably additionally checking
CONFIG_64BIT instead.

Thanks,
Chao
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Huang, Kai]

On Wed, 2022-12-21 at 21:39 +0800, Chao Peng wrote:
> > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > > > > > > > > > > 
> > > > > > > > > > > > [...]
> > > > > > > > > > > > 
> > > > > > > > > > > > > > +
> > > > > > > > > > > > > > +	/*
> > > > > > > > > > > > > > +	 * These pages are currently unmovable so don't place them into
> > > > > > > > > > > > > > movable
> > > > > > > > > > > > > > +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > > > > > > > > > > > > > +	 */
> > > > > > > > > > > > > > +	mapping = memfd->f_mapping;
> > > > > > > > > > > > > > +	mapping_set_unevictable(mapping);
> > > > > > > > > > > > > > +	mapping_set_gfp_mask(mapping,
> > > > > > > > > > > > > > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > > > > > > > > > > > 
> > > > > > > > > > > > But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from
> > > > > > > > > > > > non-
> > > > > > > > > > > > movable zones, but doesn't necessarily prevent page from being migrated.  My
> > > > > > > > > > > > first glance is you need to implement either a_ops->migrate_folio() or just
> > > > > > > > > > > > get_page() after faulting in the page to prevent.
> > > > > > > > > > 
> > > > > > > > > > The current api restrictedmem_get_page() already does this, after the
> > > > > > > > > > caller calling it, it holds a reference to the page. The caller then
> > > > > > > > > > decides when to call put_page() appropriately.
> > > > > > > > 
> > > > > > > > I tried to dig some history. Perhaps I am missing something, but it seems Kirill
> > > > > > > > said in v9 that this code doesn't prevent page migration, and we need to
> > > > > > > > increase page refcount in restrictedmem_get_page():
> > > > > > > > 
> > > > > > > > https://lore.kernel.org/linux-mm/20221129112139.usp6dqhbih47qpjl@box.shutemov.name/
> > > > > > > > 
> > > > > > > > But looking at this series it seems restrictedmem_get_page() in this v10 is
> > > > > > > > identical to the one in v9 (except v10 uses 'folio' instead of 'page')?
> > > > > > 
> > > > > > restrictedmem_get_page() increases page refcount several versions ago so
> > > > > > no change in v10 is needed. You probably missed my reply:
> > > > > > 
> > > > > > https://lore.kernel.org/linux-mm/20221129135844.GA902164@chaop.bj.intel.com/
> > > > 
> > > > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > > > refcount after setting up mapping in the secondary mmu, otherwise the page will
> > > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> > 
> > That's true. Actually even true for restrictedmem case, most likely we
> > will still need the kvm_release_pfn_clean() for KVM generic code. On one
> > side, other restrictedmem users like pKVM may not require page pinning
> > at all. On the other side, see below.

OK. Agreed.

> > 
> > > > 
> > > > So what we are expecting is: for KVM if the page comes from restricted mem, then
> > > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.
> > 
> > I argue that this page pinning (or page migration prevention) is not
> > tied to where the page comes from, instead related to how the page will
> > be used. Whether the page is restrictedmem backed or GUP() backed, once
> > it's used by current version of TDX then the page pinning is needed. So
> > such page migration prevention is really TDX thing, even not KVM generic
> > thing (that's why I think we don't need change the existing logic of
> > kvm_release_pfn_clean()). 
> > 

This essentially boils down to who "owns" page migration handling, and sadly,
page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
migration by itself -- it's just a passive receiver.

For normal pages, page migration is totally done by the core-kernel (i.e. it
unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
>migrate_page() to actually migrate the page).

In the sense of TDX, conceptually it should be done in the same way. The more
important thing is: yes KVM can use get_page() to prevent page migration, but
when KVM wants to support it, KVM cannot just remove get_page(), as the core-
kernel will still just do migrate_page() which won't work for TDX (given
restricted_memfd doesn't have a_ops->migrate_page() implemented).

So I think the restricted_memfd filesystem should own page migration handling,
(i.e. by implementing a_ops->migrate_page() to either just reject page migration
or somehow support it).

To support page migration, it may require KVM's help in case of TDX (the
TDH.MEM.PAGE.RELOCATE SEAMCALL requires "GPA" and "level" of EPT mapping, which
are only available in KVM), but that doesn't make KVM to own the handling of
page migration.


> > Wouldn't better to let TDX code (or who
> > requires that) to increase/decrease the refcount when it populates/drops
> > the secure EPT entries? This is exactly what the current TDX code does:
> > 
> > get_page():
> > https://github.com/intel/tdx/blob/kvm-upstream/arch/x86/kvm/vmx/tdx.c#L1217
> > 
> > put_page():
> > https://github.com/intel/tdx/blob/kvm-upstream/arch/x86/kvm/vmx/tdx.c#L1334
> > 

As explained above, I think doing so in KVM is wrong: it can prevent by using
get_page(), but you cannot simply remove it to support page migration.

Sean also said similar thing when reviewing v8 KVM TDX series and I also agree:

https://lore.kernel.org/lkml/Yvu5PsAndEbWKTHc@google.com/
https://lore.kernel.org/lkml/31fec1b4438a6d9bb7ff719f96caa8b23ed764d6.camel@intel.com/

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Sean Christopherson]

On Wed, Dec 21, 2022, Chao Peng wrote:
> On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > refcount after setting up mapping in the secondary mmu, otherwise the page will
> > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> 
> That's true. Actually even true for restrictedmem case, most likely we
> will still need the kvm_release_pfn_clean() for KVM generic code. On one
> side, other restrictedmem users like pKVM may not require page pinning
> at all. On the other side, see below.
> 
> > 
> > So what we are expecting is: for KVM if the page comes from restricted mem, then
> > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.

No, requiring the user (KVM) to guard against lack of support for page migration
in restricted mem is a terrible API.  It's totally fine for restricted mem to not
support page migration until there's a use case, but punting the problem to KVM
is not acceptable.  Restricted mem itself doesn't yet support page migration,
e.g. explosions would occur even if KVM wanted to allow migration since there is
no notification to invalidate existing mappings.

> I argue that this page pinning (or page migration prevention) is not
> tied to where the page comes from, instead related to how the page will
> be used. Whether the page is restrictedmem backed or GUP() backed, once
> it's used by current version of TDX then the page pinning is needed. So
> such page migration prevention is really TDX thing, even not KVM generic
> thing (that's why I think we don't need change the existing logic of
> kvm_release_pfn_clean()). Wouldn't better to let TDX code (or who
> requires that) to increase/decrease the refcount when it populates/drops
> the secure EPT entries? This is exactly what the current TDX code does:

I agree that whether or not migration is supported should be controllable by the
user, but I strongly disagree on punting refcount management to KVM (or TDX).
The whole point of restricted mem is to support technologies like TDX and SNP,
accomodating their special needs for things like page migration should be part of
the API, not some footnote in the documenation.

It's not difficult to let the user communicate support for page migration, e.g.
if/when restricted mem gains support, add a hook to restrictedmem_notifier_ops
to signal support (or lack thereof) for page migration.  NULL == no migration,
non-NULL == migration allowed.

We know that supporting page migration in TDX and SNP is possible, and we know
that page migration will require a dedicated API since the backing store can't
memcpy() the page.  I don't see any reason to ignore that eventuality.

But again, unless I'm missing something, that's a future problem because restricted
mem doesn't yet support page migration regardless of the downstream user.

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Huang, Kai]

On Thu, 2022-12-22 at 18:15 +0000, Sean Christopherson wrote:
> On Wed, Dec 21, 2022, Chao Peng wrote:
> > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > > refcount after setting up mapping in the secondary mmu, otherwise the page will
> > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> > 
> > That's true. Actually even true for restrictedmem case, most likely we
> > will still need the kvm_release_pfn_clean() for KVM generic code. On one
> > side, other restrictedmem users like pKVM may not require page pinning
> > at all. On the other side, see below.
> > 
> > > 
> > > So what we are expecting is: for KVM if the page comes from restricted mem, then
> > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.
> 
> No, requiring the user (KVM) to guard against lack of support for page migration
> in restricted mem is a terrible API.  It's totally fine for restricted mem to not
> support page migration until there's a use case, but punting the problem to KVM
> is not acceptable.  Restricted mem itself doesn't yet support page migration,
> e.g. explosions would occur even if KVM wanted to allow migration since there is
> no notification to invalidate existing mappings.
> 
> 

Yes totally agree (I also replied separately).

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Thu, Dec 22, 2022 at 12:37:19AM +0000, Huang, Kai wrote:
> On Wed, 2022-12-21 at 21:39 +0800, Chao Peng wrote:
> > > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > > > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > > > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > > > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > > > > > > > > > > > 
> > > > > > > > > > > > > [...]
> > > > > > > > > > > > > 
> > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > +	/*
> > > > > > > > > > > > > > > +	 * These pages are currently unmovable so don't place them into
> > > > > > > > > > > > > > > movable
> > > > > > > > > > > > > > > +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> > > > > > > > > > > > > > > +	 */
> > > > > > > > > > > > > > > +	mapping = memfd->f_mapping;
> > > > > > > > > > > > > > > +	mapping_set_unevictable(mapping);
> > > > > > > > > > > > > > > +	mapping_set_gfp_mask(mapping,
> > > > > > > > > > > > > > > +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > > > > > > > > > > > > 
> > > > > > > > > > > > > But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from
> > > > > > > > > > > > > non-
> > > > > > > > > > > > > movable zones, but doesn't necessarily prevent page from being migrated.  My
> > > > > > > > > > > > > first glance is you need to implement either a_ops->migrate_folio() or just
> > > > > > > > > > > > > get_page() after faulting in the page to prevent.
> > > > > > > > > > > 
> > > > > > > > > > > The current api restrictedmem_get_page() already does this, after the
> > > > > > > > > > > caller calling it, it holds a reference to the page. The caller then
> > > > > > > > > > > decides when to call put_page() appropriately.
> > > > > > > > > 
> > > > > > > > > I tried to dig some history. Perhaps I am missing something, but it seems Kirill
> > > > > > > > > said in v9 that this code doesn't prevent page migration, and we need to
> > > > > > > > > increase page refcount in restrictedmem_get_page():
> > > > > > > > > 
> > > > > > > > > https://lore.kernel.org/linux-mm/20221129112139.usp6dqhbih47qpjl@box.shutemov.name/
> > > > > > > > > 
> > > > > > > > > But looking at this series it seems restrictedmem_get_page() in this v10 is
> > > > > > > > > identical to the one in v9 (except v10 uses 'folio' instead of 'page')?
> > > > > > > 
> > > > > > > restrictedmem_get_page() increases page refcount several versions ago so
> > > > > > > no change in v10 is needed. You probably missed my reply:
> > > > > > > 
> > > > > > > https://lore.kernel.org/linux-mm/20221129135844.GA902164@chaop.bj.intel.com/
> > > > > 
> > > > > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > > > > refcount after setting up mapping in the secondary mmu, otherwise the page will
> > > > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> > > 
> > > That's true. Actually even true for restrictedmem case, most likely we
> > > will still need the kvm_release_pfn_clean() for KVM generic code. On one
> > > side, other restrictedmem users like pKVM may not require page pinning
> > > at all. On the other side, see below.
> 
> OK. Agreed.
> 
> > > 
> > > > > 
> > > > > So what we are expecting is: for KVM if the page comes from restricted mem, then
> > > > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.
> > > 
> > > I argue that this page pinning (or page migration prevention) is not
> > > tied to where the page comes from, instead related to how the page will
> > > be used. Whether the page is restrictedmem backed or GUP() backed, once
> > > it's used by current version of TDX then the page pinning is needed. So
> > > such page migration prevention is really TDX thing, even not KVM generic
> > > thing (that's why I think we don't need change the existing logic of
> > > kvm_release_pfn_clean()). 
> > > 
> 
> This essentially boils down to who "owns" page migration handling, and sadly,
> page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
> migration by itself -- it's just a passive receiver.

No, I'm not talking on the page migration handling itself, I know page
migration requires coordination from both core-mm and KVM. I'm more
concerning on the page migration prevention here. This is something we
need to address for TDX before the page migration is supported.

> 
> For normal pages, page migration is totally done by the core-kernel (i.e. it
> unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
> >migrate_page() to actually migrate the page).
> 
> In the sense of TDX, conceptually it should be done in the same way. The more
> important thing is: yes KVM can use get_page() to prevent page migration, but
> when KVM wants to support it, KVM cannot just remove get_page(), as the core-
> kernel will still just do migrate_page() which won't work for TDX (given
> restricted_memfd doesn't have a_ops->migrate_page() implemented).
> 
> So I think the restricted_memfd filesystem should own page migration handling,
> (i.e. by implementing a_ops->migrate_page() to either just reject page migration
> or somehow support it).
> 
> To support page migration, it may require KVM's help in case of TDX (the
> TDH.MEM.PAGE.RELOCATE SEAMCALL requires "GPA" and "level" of EPT mapping, which
> are only available in KVM), but that doesn't make KVM to own the handling of
> page migration.
> 
> 
> > > Wouldn't better to let TDX code (or who
> > > requires that) to increase/decrease the refcount when it populates/drops
> > > the secure EPT entries? This is exactly what the current TDX code does:
> > > 
> > > get_page():
> > > https://github.com/intel/tdx/blob/kvm-upstream/arch/x86/kvm/vmx/tdx.c#L1217
> > > 
> > > put_page():
> > > https://github.com/intel/tdx/blob/kvm-upstream/arch/x86/kvm/vmx/tdx.c#L1334
> > > 
> 
> As explained above, I think doing so in KVM is wrong: it can prevent by using
> get_page(), but you cannot simply remove it to support page migration.

Removing get_page() is definitely not enough for page migration support.
But the key thing is for page migration prevention, other than
get_page(), do we really have alternative.

Thanks,
Chao
> 
> Sean also said similar thing when reviewing v8 KVM TDX series and I also agree:
> 
> https://lore.kernel.org/lkml/Yvu5PsAndEbWKTHc@google.com/
> https://lore.kernel.org/lkml/31fec1b4438a6d9bb7ff719f96caa8b23ed764d6.camel@intel.com/
> 

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Thu, Dec 22, 2022 at 06:15:24PM +0000, Sean Christopherson wrote:
> On Wed, Dec 21, 2022, Chao Peng wrote:
> > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > > refcount after setting up mapping in the secondary mmu, otherwise the page will
> > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> > 
> > That's true. Actually even true for restrictedmem case, most likely we
> > will still need the kvm_release_pfn_clean() for KVM generic code. On one
> > side, other restrictedmem users like pKVM may not require page pinning
> > at all. On the other side, see below.
> > 
> > > 
> > > So what we are expecting is: for KVM if the page comes from restricted mem, then
> > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.
> 
> No, requiring the user (KVM) to guard against lack of support for page migration
> in restricted mem is a terrible API.  It's totally fine for restricted mem to not
> support page migration until there's a use case, but punting the problem to KVM
> is not acceptable.  Restricted mem itself doesn't yet support page migration,
> e.g. explosions would occur even if KVM wanted to allow migration since there is
> no notification to invalidate existing mappings.
> 
> > I argue that this page pinning (or page migration prevention) is not
> > tied to where the page comes from, instead related to how the page will
> > be used. Whether the page is restrictedmem backed or GUP() backed, once
> > it's used by current version of TDX then the page pinning is needed. So
> > such page migration prevention is really TDX thing, even not KVM generic
> > thing (that's why I think we don't need change the existing logic of
> > kvm_release_pfn_clean()). Wouldn't better to let TDX code (or who
> > requires that) to increase/decrease the refcount when it populates/drops
> > the secure EPT entries? This is exactly what the current TDX code does:
> 
> I agree that whether or not migration is supported should be controllable by the
> user, but I strongly disagree on punting refcount management to KVM (or TDX).
> The whole point of restricted mem is to support technologies like TDX and SNP,
> accomodating their special needs for things like page migration should be part of
> the API, not some footnote in the documenation.

I never doubt page migration should be part of restrictedmem API, but
that's not an initial implementing as we all agreed? Then before that
API being introduced, we need find a solution to prevent page migration
for TDX. Other than refcount management, do we have any other workable
solution? 

> 
> It's not difficult to let the user communicate support for page migration, e.g.
> if/when restricted mem gains support, add a hook to restrictedmem_notifier_ops
> to signal support (or lack thereof) for page migration.  NULL == no migration,
> non-NULL == migration allowed.

I know.

> 
> We know that supporting page migration in TDX and SNP is possible, and we know
> that page migration will require a dedicated API since the backing store can't
> memcpy() the page.  I don't see any reason to ignore that eventuality.

No, I'm not ignoring it. It's just about the short-term page migration
prevention before that dedicated API being introduced.

> 
> But again, unless I'm missing something, that's a future problem because restricted
> mem doesn't yet support page migration regardless of the downstream user.

It's true a future problem for page migration support itself, but page
migration prevention is not a future problem since TDX pages need to be
pinned before page migration gets supported.

Thanks,
Chao

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chenyi Qiang]

On 12/2/2022 2:13 PM, Chao Peng wrote:
> In confidential computing usages, whether a page is private or shared is
> necessary information for KVM to perform operations like page fault
> handling, page zapping etc. There are other potential use cases for
> per-page memory attributes, e.g. to make memory read-only (or no-exec,
> or exec-only, etc.) without having to modify memslots.
> 
> Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> userspace to operate on the per-page memory attributes.
>   - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
>     a guest memory range.
>   - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
>     memory attributes.
> 
> KVM internally uses xarray to store the per-page memory attributes.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> ---
>  Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
>  arch/x86/kvm/Kconfig           |  1 +
>  include/linux/kvm_host.h       |  3 ++
>  include/uapi/linux/kvm.h       | 17 ++++++++
>  virt/kvm/Kconfig               |  3 ++
>  virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
>  6 files changed, 163 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 5617bc4f899f..bb2f709c0900 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
>  The "pad" and "reserved" fields may be used for future extensions and should be
>  set to 0s by userspace.
>  
> +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: u64 memory attributes bitmask(out)
> +:Returns: 0 on success, <0 on error
> +
> +Returns supported memory attributes bitmask. Supported memory attributes will
> +have the corresponding bits set in u64 memory attributes bitmask.
> +
> +The following memory attributes are defined::
> +
> +  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> +
> +4.139 KVM_SET_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: struct kvm_memory_attributes(in/out)
> +:Returns: 0 on success, <0 on error
> +
> +Sets memory attributes for pages in a guest memory range. Parameters are
> +specified via the following structure::
> +
> +  struct kvm_memory_attributes {
> +	__u64 address;
> +	__u64 size;
> +	__u64 attributes;
> +	__u64 flags;
> +  };
> +
> +The user sets the per-page memory attributes to a guest memory range indicated
> +by address/size, and in return KVM adjusts address and size to reflect the
> +actual pages of the memory range have been successfully set to the attributes.
> +If the call returns 0, "address" is updated to the last successful address + 1
> +and "size" is updated to the remaining address size that has not been set
> +successfully. The user should check the return value as well as the size to
> +decide if the operation succeeded for the whole range or not. The user may want
> +to retry the operation with the returned address/size if the previous range was
> +partially successful.
> +
> +Both address and size should be page aligned and the supported attributes can be
> +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> +
> +The "flags" field may be used for future extensions and should be set to 0s.
> +
>  5. The kvm_run structure
>  ========================
>  
> @@ -8270,6 +8323,16 @@ structure.
>  When getting the Modified Change Topology Report value, the attr->addr
>  must point to a byte where the value will be stored or retrieved from.
>  
> +8.40 KVM_CAP_MEMORY_ATTRIBUTES
> +------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm
> +
> +This capability indicates KVM supports per-page memory attributes and ioctls
> +KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available.
> +
>  9. Known KVM API problems
>  =========================
>  
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index fbeaa9ddef59..a8e379a3afee 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -49,6 +49,7 @@ config KVM
>  	select SRCU
>  	select INTERVAL_TREE
>  	select HAVE_KVM_PM_NOTIFIER if PM
> +	select HAVE_KVM_MEMORY_ATTRIBUTES
>  	help
>  	  Support hosting fully virtualized guest machines using hardware
>  	  virtualization extensions.  You will need a fairly recent
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8f874a964313..a784e2b06625 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -800,6 +800,9 @@ struct kvm {
>  
>  #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
>  	struct notifier_block pm_notifier;
> +#endif
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	struct xarray mem_attr_array;
>  #endif
>  	char stats_id[KVM_STATS_NAME_SIZE];
>  };
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 64dfe9c07c87..5d0941acb5bb 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1182,6 +1182,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_S390_CPU_TOPOLOGY 222
>  #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
>  #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
> +#define KVM_CAP_MEMORY_ATTRIBUTES 225
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -2238,4 +2239,20 @@ struct kvm_s390_zpci_op {
>  /* flags for kvm_s390_zpci_op->u.reg_aen.flags */
>  #define KVM_S390_ZPCIOP_REGAEN_HOST    (1 << 0)
>  
> +/* Available with KVM_CAP_MEMORY_ATTRIBUTES */
> +#define KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES    _IOR(KVMIO,  0xd2, __u64)
> +#define KVM_SET_MEMORY_ATTRIBUTES              _IOWR(KVMIO,  0xd3, struct kvm_memory_attributes)
> +
> +struct kvm_memory_attributes {
> +	__u64 address;
> +	__u64 size;
> +	__u64 attributes;
> +	__u64 flags;
> +};
> +
> +#define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +#define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +#define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +#define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> +
>  #endif /* __LINUX_KVM_H */
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 800f9470e36b..effdea5dd4f0 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -19,6 +19,9 @@ config HAVE_KVM_IRQ_ROUTING
>  config HAVE_KVM_DIRTY_RING
>         bool
>  
> +config HAVE_KVM_MEMORY_ATTRIBUTES
> +       bool
> +
>  # Only strongly ordered architectures can select this, as it doesn't
>  # put any explicit constraint on userspace ordering. They can also
>  # select the _ACQ_REL version.
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1782c4555d94..7f0f5e9f2406 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>  	spin_lock_init(&kvm->mn_invalidate_lock);
>  	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
>  	xa_init(&kvm->vcpu_array);
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	xa_init(&kvm->mem_attr_array);
> +#endif
>  
>  	INIT_LIST_HEAD(&kvm->gpc_list);
>  	spin_lock_init(&kvm->gpc_lock);
> @@ -1323,6 +1326,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
>  		kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
>  		kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
>  	}
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	xa_destroy(&kvm->mem_attr_array);
> +#endif
>  	cleanup_srcu_struct(&kvm->irq_srcu);
>  	cleanup_srcu_struct(&kvm->srcu);
>  	kvm_arch_free_vm(kvm);
> @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
>  }
>  #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
>  
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> +{
> +	return 0;
> +}
> +
> +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> +					   struct kvm_memory_attributes *attrs)
> +{
> +	gfn_t start, end;
> +	unsigned long i;
> +	void *entry;
> +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> +
> +	/* flags is currently not used. */
> +	if (attrs->flags)
> +		return -EINVAL;
> +	if (attrs->attributes & ~supported_attrs)
> +		return -EINVAL;
> +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> +		return -EINVAL;
> +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> +		return -EINVAL;
> +
> +	start = attrs->address >> PAGE_SHIFT;
> +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> +
> +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> +

Because guest memory defaults to private, and now this patch stores the
attributes with KVM_MEMORY_ATTRIBUTE_PRIVATE instead of _SHARED, it
would bring more KVM_EXIT_MEMORY_FAULT exits at the beginning of boot
time. Maybe it can be optimized somehow in other places? e.g. set mem
attr in advance.

> +	mutex_lock(&kvm->lock);
> +	for (i = start; i < end; i++)
> +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> +				    GFP_KERNEL_ACCOUNT)))
> +			break;
> +	mutex_unlock(&kvm->lock);
> +
> +	attrs->address = i << PAGE_SHIFT;
> +	attrs->size = (end - i) << PAGE_SHIFT;
> +
> +	return 0;
> +}
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +
>  struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
>  {
>  	return __gfn_to_memslot(kvm_memslots(kvm), gfn);

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Wed, Dec 28, 2022 at 04:28:01PM +0800, Chenyi Qiang wrote:
...
> > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > +					   struct kvm_memory_attributes *attrs)
> > +{
> > +	gfn_t start, end;
> > +	unsigned long i;
> > +	void *entry;
> > +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +	/* flags is currently not used. */
> > +	if (attrs->flags)
> > +		return -EINVAL;
> > +	if (attrs->attributes & ~supported_attrs)
> > +		return -EINVAL;
> > +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > +		return -EINVAL;
> > +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > +		return -EINVAL;
> > +
> > +	start = attrs->address >> PAGE_SHIFT;
> > +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> > +
> > +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > +
> 
> Because guest memory defaults to private, and now this patch stores the
> attributes with KVM_MEMORY_ATTRIBUTE_PRIVATE instead of _SHARED, it
> would bring more KVM_EXIT_MEMORY_FAULT exits at the beginning of boot
> time. Maybe it can be optimized somehow in other places? e.g. set mem
> attr in advance.

KVM defaults to 'shared' because this ioctl can also be potentially used
by normal VMs and 'shared' sounds a value meaningful for both normal VMs
and confidential VMs. As for more KVM_EXIT_MEMORY_FAULT exits during the
booting time, yes, setting all memory to 'private' for confidential VMs
through this ioctl in userspace before guest launch is an approach for
KVM userspace to 'override' the KVM default and reduce the number of
implicit conversions.

Thanks,
Chao
> 
> > +	mutex_lock(&kvm->lock);
> > +	for (i = start; i < end; i++)
> > +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > +				    GFP_KERNEL_ACCOUNT)))
> > +			break;
> > +	mutex_unlock(&kvm->lock);
> > +
> > +	attrs->address = i << PAGE_SHIFT;
> > +	attrs->size = (end - i) << PAGE_SHIFT;
> > +
> > +	return 0;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > +
> >  struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
> >  {
> >  	return __gfn_to_memslot(kvm_memslots(kvm), gfn);

RE: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Wang, Wei W]

On Tuesday, January 3, 2023 9:40 AM, Chao Peng wrote:
> > Because guest memory defaults to private, and now this patch stores
> > the attributes with KVM_MEMORY_ATTRIBUTE_PRIVATE instead of
> _SHARED,
> > it would bring more KVM_EXIT_MEMORY_FAULT exits at the beginning of
> > boot time. Maybe it can be optimized somehow in other places? e.g. set
> > mem attr in advance.
> 
> KVM defaults to 'shared' because this ioctl can also be potentially used by
> normal VMs and 'shared' sounds a value meaningful for both normal VMs and
> confidential VMs. 

Do you mean a normal VM could have pages marked private? What's the usage?
(If all the pages are just marked shared for normal VMs, then why do we need it)

> As for more KVM_EXIT_MEMORY_FAULT exits during the
> booting time, yes, setting all memory to 'private' for confidential VMs through
> this ioctl in userspace before guest launch is an approach for KVM userspace to
> 'override' the KVM default and reduce the number of implicit conversions.

Most pages of a confidential VM are likely to be private pages. It seems more efficient
(and not difficult to check vm_type) to have KVM defaults to "private" for confidential VMs
and defaults to "shared" for normal VMs.

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Tue, Jan 03, 2023, Wang, Wei W wrote:
> On Tuesday, January 3, 2023 9:40 AM, Chao Peng wrote:
> > > Because guest memory defaults to private, and now this patch stores
> > > the attributes with KVM_MEMORY_ATTRIBUTE_PRIVATE instead of
> > _SHARED,
> > > it would bring more KVM_EXIT_MEMORY_FAULT exits at the beginning of
> > > boot time. Maybe it can be optimized somehow in other places? e.g. set
> > > mem attr in advance.
> > 
> > KVM defaults to 'shared' because this ioctl can also be potentially used by
> > normal VMs and 'shared' sounds a value meaningful for both normal VMs and
> > confidential VMs. 
> 
> Do you mean a normal VM could have pages marked private? What's the usage?
> (If all the pages are just marked shared for normal VMs, then why do we need it)

No, there are potential use cases for per-page attribute/permissions, e.g. to
make select pages read-only, exec-only, no-exec, etc...

> > As for more KVM_EXIT_MEMORY_FAULT exits during the
> > booting time, yes, setting all memory to 'private' for confidential VMs through
> > this ioctl in userspace before guest launch is an approach for KVM userspace to
> > 'override' the KVM default and reduce the number of implicit conversions.
> 
> Most pages of a confidential VM are likely to be private pages. It seems more efficient
> (and not difficult to check vm_type) to have KVM defaults to "private" for confidential VMs
> and defaults to "shared" for normal VMs.

If done right, the default shouldn't matter all that much for efficiency.  KVM
needs to be able to effeciently track large ranges regardless of the default,
otherwise the memory overhead and the presumably cost of lookups will be painful.
E.g. converting a 1GiB chunk to shared should ideally require one entry, not 256k
entries.

Looks like that behavior was changed in v8 in response to feedback[*] that doing
xa_store_range() on a subset of an existing range (entry) would overwrite the
entire existing range (entry), not just the smaller subset.  xa_store_range() does
appear to be too simplistic for this use case, but looking at __filemap_add_folio(),
splitting an existing entry isn't super complex.

Using xa_store() for the very initial implementation is ok, and probably a good
idea since it's more obviously correct and will give us a bisection point.  But
we definitely want a more performant implementation sooner than later.  The hardest
part will likely be merging existing entries, but that can be done separately too,
and is probably lower priority.

E.g. (1) use xa_store() and always track at 4KiB granularity, (2) support storing
metadata in multi-index entries, and finally (3) support merging adjacent entries
with identical values.

[*] https://lore.kernel.org/all/CAGtprH9xyw6bt4=RBWF6-v2CSpabOCpKq5rPz+e-9co7EisoVQ@mail.gmail.com

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Tue, Jan 03, 2023 at 11:06:37PM +0000, Sean Christopherson wrote:
> On Tue, Jan 03, 2023, Wang, Wei W wrote:
> > On Tuesday, January 3, 2023 9:40 AM, Chao Peng wrote:
> > > > Because guest memory defaults to private, and now this patch stores
> > > > the attributes with KVM_MEMORY_ATTRIBUTE_PRIVATE instead of
> > > _SHARED,
> > > > it would bring more KVM_EXIT_MEMORY_FAULT exits at the beginning of
> > > > boot time. Maybe it can be optimized somehow in other places? e.g. set
> > > > mem attr in advance.
> > > 
> > > KVM defaults to 'shared' because this ioctl can also be potentially used by
> > > normal VMs and 'shared' sounds a value meaningful for both normal VMs and
> > > confidential VMs. 
> > 
> > Do you mean a normal VM could have pages marked private? What's the usage?
> > (If all the pages are just marked shared for normal VMs, then why do we need it)
> 
> No, there are potential use cases for per-page attribute/permissions, e.g. to
> make select pages read-only, exec-only, no-exec, etc...

Right, normal VMs are not likely use private/shared bit. Not sure pKVM,
but perhaps not call it 'normal' VMs in this context. But since the
ioctl can be used by normal VMs for other bits (read-only, exec-only,
no-exec, etc), a default 'private' looks strange for them. That's why I
default it to 'shared' and for confidential guest, we can issue another
call to this ioctl to set all the memory to 'private' before guest
booting, if default 'private' is needed for guest.

Like Wei mentioned, it's also possible to make the default dependents on
vm_type, but that looks awkward to me from the API definition as well as
the implementation, also the vm_type has not been introduced at this time.

> 
> > > As for more KVM_EXIT_MEMORY_FAULT exits during the
> > > booting time, yes, setting all memory to 'private' for confidential VMs through
> > > this ioctl in userspace before guest launch is an approach for KVM userspace to
> > > 'override' the KVM default and reduce the number of implicit conversions.
> > 
> > Most pages of a confidential VM are likely to be private pages. It seems more efficient
> > (and not difficult to check vm_type) to have KVM defaults to "private" for confidential VMs
> > and defaults to "shared" for normal VMs.
> 
> If done right, the default shouldn't matter all that much for efficiency.  KVM
> needs to be able to effeciently track large ranges regardless of the default,
> otherwise the memory overhead and the presumably cost of lookups will be painful.
> E.g. converting a 1GiB chunk to shared should ideally require one entry, not 256k
> entries.

I agree, KVM should have the ability to track large ranges efficiently.

> 
> Looks like that behavior was changed in v8 in response to feedback[*] that doing
> xa_store_range() on a subset of an existing range (entry) would overwrite the
> entire existing range (entry), not just the smaller subset.  xa_store_range() does
> appear to be too simplistic for this use case, but looking at __filemap_add_folio(),
> splitting an existing entry isn't super complex.

Yes, xa_store_range() looks a perfect match for us initially but the
'overwriting the entire entry' behavior makes it incorrect for us when
storing a subset on an existing large entry. xarray lib has utilities
for splitting, the hard part is merging existing entries, as you also
said below. Thanks for pointing out the __filemap_add_folio() example,
it does look not too complex for splitting.

> 
> Using xa_store() for the very initial implementation is ok, and probably a good
> idea since it's more obviously correct and will give us a bisection point.  But
> we definitely want a more performant implementation sooner than later.  The hardest
> part will likely be merging existing entries, but that can be done separately too,
> and is probably lower priority.
> 
> E.g. (1) use xa_store() and always track at 4KiB granularity, (2) support storing
> metadata in multi-index entries, and finally (3) support merging adjacent entries
> with identical values.

This path looks good to me.

Thanks,
Chao
> 
> [*] https://lore.kernel.org/all/CAGtprH9xyw6bt4=RBWF6-v2CSpabOCpKq5rPz+e-9co7EisoVQ@mail.gmail.com

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Jarkko Sakkinen]

On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> In memory encryption usage, guest memory may be encrypted with special
> key and can be accessed only by the guest itself. We call such memory
> private memory. It's valueless and sometimes can cause problem to allow
> userspace to access guest private memory. This new KVM memslot extension
> allows guest private memory being provided through a restrictedmem
> backed file descriptor(fd) and userspace is restricted to access the
> bookmarked memory in the fd.
> 
> This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> additional KVM memslot fields restricted_fd/restricted_offset to allow
> userspace to instruct KVM to provide guest memory through restricted_fd.
> 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> and the size is 'memory_size'.
> 
> The extended memslot can still have the userspace_addr(hva). When use, a
> single memslot can maintain both private memory through restricted_fd
> and shared memory through userspace_addr. Whether the private or shared
> part is visible to guest is maintained by other KVM code.
> 
> A restrictedmem_notifier field is also added to the memslot structure to
> allow the restricted_fd's backing store to notify KVM the memory change,
> KVM then can invalidate its page table entries or handle memory errors.
> 
> Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> and right now it is selected on X86_64 only.
> 
> To make future maintenance easy, internally use a binary compatible
> alias struct kvm_user_mem_region to handle both the normal and the
> '_ext' variants.

Feels bit hacky IMHO, and more like a completely new feature than
an extension.

Why not just add a new ioctl? The commit message does not address
the most essential design here.

BR, Jarkko

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Vishal Annapurve]

On Thu, Dec 1, 2022 at 10:20 PM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
> +                                        pgoff_t start, pgoff_t end,
> +                                        gfn_t *gfn_start, gfn_t *gfn_end)
> +{
> +       unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> +
> +       if (start > base_pgoff)
> +               *gfn_start = slot->base_gfn + start - base_pgoff;

There should be a check for overflow here in case start is a very big
value. Additional check can look like:
if (start >= base_pgoff + slot->npages)
       return false;

> +       else
> +               *gfn_start = slot->base_gfn;
> +
> +       if (end < base_pgoff + slot->npages)
> +               *gfn_end = slot->base_gfn + end - base_pgoff;

If "end" is smaller than base_pgoff, this can cause overflow and
return the range as valid. There should be additional check:
if (end < base_pgoff)
         return false;


> +       else
> +               *gfn_end = slot->base_gfn + slot->npages;
> +
> +       if (*gfn_start >= *gfn_end)
> +               return false;
> +
> +       return true;
> +}
> +

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Thu, Jan 05, 2023 at 12:38:30PM -0800, Vishal Annapurve wrote:
> On Thu, Dec 1, 2022 at 10:20 PM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > +static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
> > +                                        pgoff_t start, pgoff_t end,
> > +                                        gfn_t *gfn_start, gfn_t *gfn_end)
> > +{
> > +       unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> > +
> > +       if (start > base_pgoff)
> > +               *gfn_start = slot->base_gfn + start - base_pgoff;
> 
> There should be a check for overflow here in case start is a very big
> value. Additional check can look like:
> if (start >= base_pgoff + slot->npages)
>        return false;
> 
> > +       else
> > +               *gfn_start = slot->base_gfn;
> > +
> > +       if (end < base_pgoff + slot->npages)
> > +               *gfn_end = slot->base_gfn + end - base_pgoff;
> 
> If "end" is smaller than base_pgoff, this can cause overflow and
> return the range as valid. There should be additional check:
> if (end < base_pgoff)
>          return false;

Thanks! Both are good catches. The improved code:

static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
					 pgoff_t start, pgoff_t end,
					 gfn_t *gfn_start, gfn_t *gfn_end)
{
	unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;

	if (start >= base_pgoff + slot->npages)
		return false;
	else if (start <= base_pgoff)
		*gfn_start = slot->base_gfn;
	else
		*gfn_start = start - base_pgoff + slot->base_gfn;

	if (end <= base_pgoff)
		return false;
	else if (end >= base_pgoff + slot->npages)
		*gfn_end = slot->base_gfn + slot->npages;
	else
		*gfn_end = end - base_pgoff + slot->base_gfn;

	if (*gfn_start >= *gfn_end)
		return false;

	return true;
}

Thanks,
Chao
> 
> 
> > +       else
> > +               *gfn_end = slot->base_gfn + slot->npages;
> > +
> > +       if (*gfn_start >= *gfn_end)
> > +               return false;
> > +
> > +       return true;
> > +}
> > +

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote:
> On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > In memory encryption usage, guest memory may be encrypted with special
> > key and can be accessed only by the guest itself. We call such memory
> > private memory. It's valueless and sometimes can cause problem to allow
> > userspace to access guest private memory. This new KVM memslot extension
> > allows guest private memory being provided through a restrictedmem
> > backed file descriptor(fd) and userspace is restricted to access the
> > bookmarked memory in the fd.
> > 
> > This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> > additional KVM memslot fields restricted_fd/restricted_offset to allow
> > userspace to instruct KVM to provide guest memory through restricted_fd.
> > 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> > and the size is 'memory_size'.
> > 
> > The extended memslot can still have the userspace_addr(hva). When use, a
> > single memslot can maintain both private memory through restricted_fd
> > and shared memory through userspace_addr. Whether the private or shared
> > part is visible to guest is maintained by other KVM code.
> > 
> > A restrictedmem_notifier field is also added to the memslot structure to
> > allow the restricted_fd's backing store to notify KVM the memory change,
> > KVM then can invalidate its page table entries or handle memory errors.
> > 
> > Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added
> > and right now it is selected on X86_64 only.
> > 
> > To make future maintenance easy, internally use a binary compatible
> > alias struct kvm_user_mem_region to handle both the normal and the
> > '_ext' variants.
> 
> Feels bit hacky IMHO, and more like a completely new feature than
> an extension.
> 
> Why not just add a new ioctl? The commit message does not address
> the most essential design here.

Yes, people can always choose to add a new ioctl for this kind of change
and the balance point here is we want to also avoid 'too many ioctls' if
the functionalities are similar.  The '_ext' variant reuses all the
existing fields in the 'normal' variant and most importantly KVM
internally can reuse most of the code. I certainly can add some words in
the commit message to explain this design choice.

Thanks,
Chao
> 
> BR, Jarkko

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Sean Christopherson]

On Fri, Jan 06, 2023, Chao Peng wrote:
> On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote:
> > On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > > To make future maintenance easy, internally use a binary compatible
> > > alias struct kvm_user_mem_region to handle both the normal and the
> > > '_ext' variants.
> > 
> > Feels bit hacky IMHO, and more like a completely new feature than
> > an extension.
> > 
> > Why not just add a new ioctl? The commit message does not address
> > the most essential design here.
> 
> Yes, people can always choose to add a new ioctl for this kind of change
> and the balance point here is we want to also avoid 'too many ioctls' if
> the functionalities are similar.  The '_ext' variant reuses all the
> existing fields in the 'normal' variant and most importantly KVM
> internally can reuse most of the code. I certainly can add some words in
> the commit message to explain this design choice.

After seeing the userspace side of this, I agree with Jarkko; overloading
KVM_SET_USER_MEMORY_REGION is a hack.  E.g. the size validation ends up being
bogus, and userspace ends up abusing unions or implementing kvm_user_mem_region
itself.

It feels absolutely ridiculous, but I think the best option is to do:

#define KVM_SET_USER_MEMORY_REGION2 _IOW(KVMIO, 0x49, \
					 struct kvm_userspace_memory_region2)

/* for KVM_SET_USER_MEMORY_REGION2 */
struct kvm_user_mem_region2 {
	__u32 slot;
	__u32 flags;
	__u64 guest_phys_addr;
	__u64 memory_size;
	__u64 userspace_addr;
	__u64 restricted_offset;
	__u32 restricted_fd;
	__u32 pad1;
	__u64 pad2[14];
}

And it's consistent with other KVM ioctls(), e.g. KVM_SET_CPUID2.

Regarding the userspace side of things, please include Vishal's selftests in v11,
it's impossible to properly review the uAPI changes without seeing the userspace
side of things.  I'm in the process of reviewing Vishal's v2[*], I'll try to
massage it into a set of patches that you can incorporate into your series.

[*] https://lore.kernel.org/all/20221205232341.4131240-1-vannapurve@google.com

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Mon, Jan 09, 2023 at 07:32:05PM +0000, Sean Christopherson wrote:
> On Fri, Jan 06, 2023, Chao Peng wrote:
> > On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote:
> > > On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > > > To make future maintenance easy, internally use a binary compatible
> > > > alias struct kvm_user_mem_region to handle both the normal and the
> > > > '_ext' variants.
> > > 
> > > Feels bit hacky IMHO, and more like a completely new feature than
> > > an extension.
> > > 
> > > Why not just add a new ioctl? The commit message does not address
> > > the most essential design here.
> > 
> > Yes, people can always choose to add a new ioctl for this kind of change
> > and the balance point here is we want to also avoid 'too many ioctls' if
> > the functionalities are similar.  The '_ext' variant reuses all the
> > existing fields in the 'normal' variant and most importantly KVM
> > internally can reuse most of the code. I certainly can add some words in
> > the commit message to explain this design choice.
> 
> After seeing the userspace side of this, I agree with Jarkko; overloading
> KVM_SET_USER_MEMORY_REGION is a hack.  E.g. the size validation ends up being
> bogus, and userspace ends up abusing unions or implementing kvm_user_mem_region
> itself.

How is the size validation being bogus? I don't quite follow. Then we
will use kvm_userspace_memory_region2 as the KVM internal alias, right?
I see similar examples use different functions to handle different
versions but it does look easier if we use alias for this function.

> 
> It feels absolutely ridiculous, but I think the best option is to do:
> 
> #define KVM_SET_USER_MEMORY_REGION2 _IOW(KVMIO, 0x49, \
> 					 struct kvm_userspace_memory_region2)

Just interesting, is 0x49 a safe number we can use? 

> 
> /* for KVM_SET_USER_MEMORY_REGION2 */
> struct kvm_user_mem_region2 {
> 	__u32 slot;
> 	__u32 flags;
> 	__u64 guest_phys_addr;
> 	__u64 memory_size;
> 	__u64 userspace_addr;
> 	__u64 restricted_offset;
> 	__u32 restricted_fd;
> 	__u32 pad1;
> 	__u64 pad2[14];
> }
> 
> And it's consistent with other KVM ioctls(), e.g. KVM_SET_CPUID2.

Okay, agree from KVM userspace API perspective this is more consistent
with similar existing examples. I see several of them.

I think we will also need a CAP_KVM_SET_USER_MEMORY_REGION2 for this new
ioctl.

> 
> Regarding the userspace side of things, please include Vishal's selftests in v11,
> it's impossible to properly review the uAPI changes without seeing the userspace
> side of things.  I'm in the process of reviewing Vishal's v2[*], I'll try to
> massage it into a set of patches that you can incorporate into your series.

Previously I included Vishal's selftests in the github repo, but not
include them in this patch series. It's OK for me to incorporate them
directly into this series and review together if Vishal is fine.

Chao
> 
> [*] https://lore.kernel.org/all/20221205232341.4131240-1-vannapurve@google.com

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Vishal Annapurve]

On Tue, Jan 10, 2023 at 1:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > Regarding the userspace side of things, please include Vishal's selftests in v11,
> > it's impossible to properly review the uAPI changes without seeing the userspace
> > side of things.  I'm in the process of reviewing Vishal's v2[*], I'll try to
> > massage it into a set of patches that you can incorporate into your series.
>
> Previously I included Vishal's selftests in the github repo, but not
> include them in this patch series. It's OK for me to incorporate them
> directly into this series and review together if Vishal is fine.
>

Yeah, I am ok with incorporating selftest patches into this series and
reviewing them together.

Regards,
Vishal

> Chao
> >
> > [*] https://lore.kernel.org/all/20221205232341.4131240-1-vannapurve@google.com

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> The system call is currently wired up for x86 arch.

Building on other architectures (except for arm64 for some reason) yields:

  CALL    /.../scripts/checksyscalls.sh
  <stdin>:1565:2: warning: #warning syscall memfd_restricted not implemented [-Wcpp]

Do we care?  It's the only such warning, which makes me think we either need to
wire this up for all architectures, or explicitly document that it's unsupported.

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---

...

> diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
> new file mode 100644
> index 000000000000..c2700c5daa43
> --- /dev/null
> +++ b/include/linux/restrictedmem.h
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _LINUX_RESTRICTEDMEM_H

Missing

 #define _LINUX_RESTRICTEDMEM_H

which causes fireworks if restrictedmem.h is included more than once.

> +#include <linux/file.h>
> +#include <linux/magic.h>
> +#include <linux/pfn_t.h>

...

> +static inline int restrictedmem_get_page(struct file *file, pgoff_t offset,
> +					 struct page **pagep, int *order)
> +{
> +	return -1;

This should be a proper -errno, though in the current incarnation of things it's
a moot point because no stub is needed.  KVM can (and should) easily provide its
own stub for this one.

> +}
> +
> +static inline bool file_is_restrictedmem(struct file *file)
> +{
> +	return false;
> +}
> +
> +static inline void restrictedmem_error_page(struct page *page,
> +					    struct address_space *mapping)
> +{
> +}
> +
> +#endif /* CONFIG_RESTRICTEDMEM */
> +
> +#endif /* _LINUX_RESTRICTEDMEM_H */

...

> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> new file mode 100644
> index 000000000000..56953c204e5c
> --- /dev/null
> +++ b/mm/restrictedmem.c
> @@ -0,0 +1,318 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "linux/sbitmap.h"
> +#include <linux/pagemap.h>
> +#include <linux/pseudo_fs.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/syscalls.h>
> +#include <uapi/linux/falloc.h>
> +#include <uapi/linux/magic.h>
> +#include <linux/restrictedmem.h>
> +
> +struct restrictedmem_data {

Any objection to simply calling this "restrictedmem"?  And then using either "rm"
or "rmem" for local variable names?  I kept reading "data" as the underyling data
being written to the page, as opposed to the metadata describing the restrictedmem
instance.

> +	struct mutex lock;
> +	struct file *memfd;
> +	struct list_head notifiers;
> +};
> +
> +static void restrictedmem_invalidate_start(struct restrictedmem_data *data,
> +					   pgoff_t start, pgoff_t end)
> +{
> +	struct restrictedmem_notifier *notifier;
> +
> +	mutex_lock(&data->lock);

This can be a r/w semaphore instead of a mutex, that way punching holes at multiple
points in the file can at least run the notifiers in parallel.  The actual allocation
by shmem will still be serialized, but I think it's worth the simple optimization
since zapping and flushing in KVM may be somewhat slow.

> +	list_for_each_entry(notifier, &data->notifiers, list) {
> +		notifier->ops->invalidate_start(notifier, start, end);

Two major design issues that we overlooked long ago:

  1. Blindly invoking notifiers will not scale.  E.g. if userspace configures a
     VM with a large number of convertible memslots that are all backed by a
     single large restrictedmem instance, then converting a single page will
     result in a linear walk through all memslots.  I don't expect anyone to
     actually do something silly like that, but I also never expected there to be
     a legitimate usecase for thousands of memslots.

  2. This approach fails to provide the ability for KVM to ensure a guest has
     exclusive access to a page.  As discussed in the past, the kernel can rely
     on hardware (and maybe ARM's pKVM implementation?) for those guarantees, but
     only for SNP and TDX VMs.  For VMs where userspace is trusted to some extent,
     e.g. SEV, there is value in ensuring a 1:1 association.

     And probably more importantly, relying on hardware for SNP and TDX yields a
     poor ABI and complicates KVM's internals.  If the kernel doesn't guarantee a
     page is exclusive to a guest, i.e. if userspace can hand out the same page
     from a restrictedmem instance to multiple VMs, then failure will occur only
     when KVM tries to assign the page to the second VM.  That will happen deep
     in KVM, which means KVM needs to gracefully handle such errors, and it means
     that KVM's ABI effectively allows plumbing garbage into its memslots.

Rather than use a simple list of notifiers, this appears to be yet another
opportunity to use an xarray.  Supporting sharing of restrictedmem will be
non-trivial, but IMO we should punt that to the future since it's still unclear
exactly how sharing will work.

An xarray will solve #1 by notifying only the consumers (memslots) that are bound
to the affected range.

And for #2, it's relatively straightforward (knock wood) to detect existing
entries, i.e. if the user wants exclusive access to memory, then the bind operation
can be reject if there's an existing entry.

VERY lightly tested code snippet at the bottom (will provide link to fully worked
code in cover letter).


> +static long restrictedmem_punch_hole(struct restrictedmem_data *data, int mode,
> +				     loff_t offset, loff_t len)
> +{
> +	int ret;
> +	pgoff_t start, end;
> +	struct file *memfd = data->memfd;
> +
> +	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> +		return -EINVAL;
> +
> +	start = offset >> PAGE_SHIFT;
> +	end = (offset + len) >> PAGE_SHIFT;
> +
> +	restrictedmem_invalidate_start(data, start, end);
> +	ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> +	restrictedmem_invalidate_end(data, start, end);

The lock needs to be end for the entire duration of the hole punch, i.e. needs to
be taken before invalidate_start() and released after invalidate_end().  If a user
(un)binds/(un)registers after invalidate_state(), it will see an unpaired notification,
e.g. could leave KVM with incorrect notifier counts.

> +
> +	return ret;
> +}

What I ended up with for an xarray-based implementation.  I'm very flexible on
names and whatnot, these are just what made sense to me.

static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
				     loff_t offset, loff_t len)
{
	struct restrictedmem_notifier *notifier;
	struct file *memfd = rm->memfd;
	unsigned long index;
	pgoff_t start, end;
	int ret;

	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
		return -EINVAL;

	start = offset >> PAGE_SHIFT;
	end = (offset + len) >> PAGE_SHIFT;

	/*
	 * Bindings must stable across invalidation to ensure the start+end
	 * are balanced.
	 */
	down_read(&rm->lock);

	xa_for_each_range(&rm->bindings, index, notifier, start, end)
		notifier->ops->invalidate_start(notifier, start, end);

	ret = memfd->f_op->fallocate(memfd, mode, offset, len);

	xa_for_each_range(&rm->bindings, index, notifier, start, end)
		notifier->ops->invalidate_end(notifier, start, end);

	up_read(&rm->lock);

	return ret;
}

int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
		       struct restrictedmem_notifier *notifier, bool exclusive)
{
	struct restrictedmem *rm = file->f_mapping->private_data;
	int ret = -EINVAL;

	down_write(&rm->lock);

	/* Non-exclusive mappings are not yet implemented. */
	if (!exclusive)
		goto out_unlock;

	if (!xa_empty(&rm->bindings)) {
		if (exclusive != rm->exclusive)
			goto out_unlock;

		if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
			goto out_unlock;
	}

	xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);
	rm->exclusive = exclusive;
	ret = 0;
out_unlock:
	up_write(&rm->lock);
	return ret;
}
EXPORT_SYMBOL_GPL(restrictedmem_bind);

void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
			  struct restrictedmem_notifier *notifier)
{
	struct restrictedmem *rm = file->f_mapping->private_data;

	down_write(&rm->lock);
	xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
	synchronize_rcu();
	up_write(&rm->lock);
}
EXPORT_SYMBOL_GPL(restrictedmem_unbind);

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index fbeaa9ddef59..a8e379a3afee 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -49,6 +49,7 @@ config KVM
>  	select SRCU
>  	select INTERVAL_TREE
>  	select HAVE_KVM_PM_NOTIFIER if PM
> +	select HAVE_KVM_MEMORY_ATTRIBUTES

I would prefer to call this KVM_GENERIC_MEMORY_ATTRIBUTES.  Similar to
KVM_GENERIC_HARDWARE_ENABLING, ARM does need/have hardware enabling, it just
doesn't want KVM's generic implementation.  In this case, pKVM does support memory
attributes, but uses stage-2 tables to track ownership and doesn't need/want the
overhead of the generic implementation.

>  	help

...

> +#define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +#define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +#define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +#define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)

I think we should carve out bits 0-2 for RWX, but I don't think we should actually
define them until they're actually accepted by KVM.

> +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> +					   struct kvm_memory_attributes *attrs)
> +{
> +	gfn_t start, end;
> +	unsigned long i;
> +	void *entry;
> +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> +
> +	/* flags is currently not used. */
> +	if (attrs->flags)
> +		return -EINVAL;
> +	if (attrs->attributes & ~supported_attrs)

Nit, no need for "supported_attrs", just consume kvm_supported_mem_attributes()
directly.

> +		return -EINVAL;
> +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> +		return -EINVAL;
> +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> +		return -EINVAL;
> +
> +	start = attrs->address >> PAGE_SHIFT;
> +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> +
> +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> +
> +	mutex_lock(&kvm->lock);

Peeking forward multiple patches, this needs to take kvm->slots_lock, not kvm->lock.
There's a bug in the lpage_disallowed patch that I believe can most easily be
solved by making this mutually exclusive with memslot changes.

When a memslot is created, KVM needs to walk through the attributes to detect
whether or not the attributes are identical for the entire slot.  To avoid races,
that means taking slots_lock.

The alternative would be to query the attributes when adjusting the hugepage level
and avoid lpage_disallowed entirely, but in the (very brief) time I've thought
about this I haven't come up with a way to do that in a performant manner.

> +	for (i = start; i < end; i++)

Curly braces needed on the for-loop.

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Sean Christopherson]

On Tue, Jan 10, 2023, Chao Peng wrote:
> On Mon, Jan 09, 2023 at 07:32:05PM +0000, Sean Christopherson wrote:
> > On Fri, Jan 06, 2023, Chao Peng wrote:
> > > On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote:
> > > > On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > > > > To make future maintenance easy, internally use a binary compatible
> > > > > alias struct kvm_user_mem_region to handle both the normal and the
> > > > > '_ext' variants.
> > > > 
> > > > Feels bit hacky IMHO, and more like a completely new feature than
> > > > an extension.
> > > > 
> > > > Why not just add a new ioctl? The commit message does not address
> > > > the most essential design here.
> > > 
> > > Yes, people can always choose to add a new ioctl for this kind of change
> > > and the balance point here is we want to also avoid 'too many ioctls' if
> > > the functionalities are similar.  The '_ext' variant reuses all the
> > > existing fields in the 'normal' variant and most importantly KVM
> > > internally can reuse most of the code. I certainly can add some words in
> > > the commit message to explain this design choice.
> > 
> > After seeing the userspace side of this, I agree with Jarkko; overloading
> > KVM_SET_USER_MEMORY_REGION is a hack.  E.g. the size validation ends up being
> > bogus, and userspace ends up abusing unions or implementing kvm_user_mem_region
> > itself.
> 
> How is the size validation being bogus? I don't quite follow.

The ioctl() magic embeds the size of the payload (struct kvm_userspace_memory_region
in this case) in the ioctl() number, and that information is visible to userspace
via _IOCTL_SIZE().  Attempting to take a larger size can mess up sanity checks,
e.g. KVM selftests get tripped up on this assert if KVM_SET_USER_MEMORY_REGION is
passed an "extended" struct.

	#define kvm_do_ioctl(fd, cmd, arg)						\
	({										\
		kvm_static_assert(!_IOC_SIZE(cmd) || sizeof(*arg) == _IOC_SIZE(cmd));	\
		ioctl(fd, cmd, arg);							\
	})

> Then we will use kvm_userspace_memory_region2 as the KVM internal alias,
> right?

Yep.

> I see similar examples use different functions to handle different versions
> but it does look easier if we use alias for this function.
> 
> > 
> > It feels absolutely ridiculous, but I think the best option is to do:
> > 
> > #define KVM_SET_USER_MEMORY_REGION2 _IOW(KVMIO, 0x49, \
> > 					 struct kvm_userspace_memory_region2)
> 
> Just interesting, is 0x49 a safe number we can use? 

Yes?  So long as its not used by KVM, it's safe.  AFAICT, it's unused.

Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> @@ -785,11 +786,12 @@ struct kvm {
>  
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  	struct mmu_notifier mmu_notifier;
> +#endif
>  	unsigned long mmu_invalidate_seq;
>  	long mmu_invalidate_in_progress;
>  	gfn_t mmu_invalidate_range_start;
>  	gfn_t mmu_invalidate_range_end;
> -#endif

Blech.  The existing code is a bit ugly, and trying to extend for this use case
makes things even worse.

Rather than use the base MMU_NOTIFIER Kconfig and an arbitrary define, I think we
should first add a proper Kconfig, e.g. KVM_GENERIC_MMU_NOTIFIER, to replace the
combination.  E.g

	config KVM_GENERIC_MMU_NOTIFIER
	       select MMU_NOTIFIER
	       bool

and then all architectures that currently #define KVM_ARCH_WANT_MMU_NOTIFIER can
simply select the Kconfig, which is everything except s390.  "GENERIC" again because
s390 does select MMU_NOTIFER and actually registers its own notifier for s390's
version of protected VMs (at least, I think that's what its "pv" stands for).

And then later down the line in this series, when the attributes and private mem
needs to tie into the notifiers, we can do:


	config KVM_GENERIC_MEMORY_ATTRIBUTES
	       select KVM_GENERIC_MMU_NOTIFIER
	       bool

I.e. that way this patch doesn't need to partially expose KVM's notifier stuff
and can instead just keep the soon-to-be-existing KVM_GENERIC_MMU_NOTIFIER.

Taking a depending on KVM_GENERIC_MMU_NOTIFIER for KVM_GENERIC_MEMORY_ATTRIBUTES
makes sense, because AFAICT, changing any type of attribute, e.g. RWX bits, is
going to necessitate unmapping the affected gfn range.

>  	struct list_head devices;
>  	u64 manual_dirty_log_protect;
>  	struct dentry *debugfs_dentry;
> @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
>  int kvm_arch_post_init_vm(struct kvm *kvm);
>  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
>  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> +bool kvm_arch_has_private_mem(struct kvm *kvm);

The reference to private memory belongs in a later patch.  More below.

> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	struct kvm_gfn_range gfn_range;
> +	struct kvm_memory_slot *slot;
> +	struct kvm_memslots *slots;
> +	struct kvm_memslot_iter iter;
> +	int i;
> +	int r = 0;

The return from kvm_unmap_gfn_range() is a bool, this should be:

	bool flush = false;

> +
> +	gfn_range.pte = __pte(0);
> +	gfn_range.may_block = true;
> +
> +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +		slots = __kvm_memslots(kvm, i);
> +
> +		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> +			slot = iter.slot;
> +			gfn_range.start = max(start, slot->base_gfn);
> +			gfn_range.end = min(end, slot->base_gfn + slot->npages);
> +			if (gfn_range.start >= gfn_range.end)
> +				continue;
> +			gfn_range.slot = slot;
> +
> +			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> +		}
> +	}
> +
> +	if (r)
> +		kvm_flush_remote_tlbs(kvm);
> +}
> +
>  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  					   struct kvm_memory_attributes *attrs)
>  {
>  	gfn_t start, end;
>  	unsigned long i;
>  	void *entry;
> +	int idx;
>  	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
>  
> -	/* flags is currently not used. */
> +	/* 'flags' is currently not used. */

Kind of a spurious change.

>  	if (attrs->flags)
>  		return -EINVAL;
>  	if (attrs->attributes & ~supported_attrs)
> @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  
>  	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
>  
> +	if (kvm_arch_has_private_mem(kvm)) {

I think we should assume that any future attributes will necessitate unmapping
and invalidation, i.e. drop the private mem check.  That allows introducing
kvm_arch_has_private_mem() in a later patch that is more directly related to
private memory.

> +		KVM_MMU_LOCK(kvm);
> +		kvm_mmu_invalidate_begin(kvm);
> +		kvm_mmu_invalidate_range_add(kvm, start, end);
> +		KVM_MMU_UNLOCK(kvm);
> +	}
> +
>  	mutex_lock(&kvm->lock);
>  	for (i = start; i < end; i++)
>  		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  			break;
>  	mutex_unlock(&kvm->lock);
>  
> +	if (kvm_arch_has_private_mem(kvm)) {
> +		idx = srcu_read_lock(&kvm->srcu);

Mostly for reference, this goes away if slots_lock is used instead of kvm->lock.

> +		KVM_MMU_LOCK(kvm);
> +		if (i > start)
> +			kvm_unmap_mem_range(kvm, start, i);
> +		kvm_mmu_invalidate_end(kvm);
> +		KVM_MMU_UNLOCK(kvm);
> +		srcu_read_unlock(&kvm->srcu, idx);
> +	}
> +
>  	attrs->address = i << PAGE_SHIFT;
>  	attrs->size = (end - i) << PAGE_SHIFT;
>  
> -- 
> 2.25.1
> 

Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 283cbb83d6ae..7772ab37ac89 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -38,6 +38,7 @@
>  #include <asm/hyperv-tlfs.h>
>  
>  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
> +#define __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES

No need for this, I think we should just make it mandatory to implement the
arch hook when CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES=y.  If another arch gains
support for mem attributes and doesn't need the hook, then we can simply add a
weak helper (or maybe add a #define then if we feel that's the way to go).

>  #define KVM_MAX_VCPUS 1024
>  
> @@ -1011,6 +1012,13 @@ struct kvm_vcpu_arch {
>  #endif
>  };
>  
> +/*
> + * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
> + * level. The remaining bits are used as a reference count.
> + */
> +#define KVM_LPAGE_PRIVATE_SHARED_MIXED		(1U << 31)

Similar to the need to unmap, I think we should just say "mixed" and ignore the
private vs. shared, i.e. make this a flag for all memory attributes.

> +#define KVM_LPAGE_COUNT_MAX			((1U << 31) - 1)

"MAX" is technically correct, but it's more of a mask.  I think we can make it a
moot point though.  There's no need to mask the count, we just want to assert that
adjusting the counting doesn't change the flag.

I would also say throw these defines into mmu.c, at least pending the bug fix
for kvm_alloc_memslot_metadata() (more on that below).

>  struct kvm_lpage_info {
>  	int disallow_lpage;
>  };
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e2c70b5afa3e..2190fd8c95c0 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -763,11 +763,16 @@ static void update_gfn_disallow_lpage_count(const struct kvm_memory_slot *slot,
>  {
>  	struct kvm_lpage_info *linfo;
>  	int i;
> +	int disallow_count;
>  
>  	for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
>  		linfo = lpage_info_slot(gfn, slot, i);
> +
> +		disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
> +		WARN_ON(disallow_count + count < 0 ||
> +			disallow_count > KVM_LPAGE_COUNT_MAX - count);
> +
>  		linfo->disallow_lpage += count;
> -		WARN_ON(linfo->disallow_lpage < 0);

It's been a long week so don't trust my math, but I believe this can simply be:

		old = linfo->disallow_lpage;
		linfo->disallow_lpage += count;

		WARN_ON_ONCE((old ^ linfo->disallow_lpage) & KVM_LPAGE_MIXED_FLAG);
>  	}
>  }
>  
> @@ -6986,3 +6991,130 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
>  	if (kvm->arch.nx_huge_page_recovery_thread)
>  		kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
>  }
> +
> +static bool linfo_is_mixed(struct kvm_lpage_info *linfo)
> +{
> +	return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +}
> +
> +static void linfo_set_mixed(gfn_t gfn, struct kvm_memory_slot *slot,
> +			    int level, bool mixed)
> +{
> +	struct kvm_lpage_info *linfo = lpage_info_slot(gfn, slot, level);
> +
> +	if (mixed)
> +		linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +	else
> +		linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +}
> +
> +static bool is_expected_attr_entry(void *entry, unsigned long expected_attrs)
> +{
> +	bool expect_private = expected_attrs & KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +
> +	if (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) {
> +		if (!expect_private)
> +			return false;
> +	} else if (expect_private)
> +		return false;

This is messy.  If we drop the private vs. shared specifity, this can go away if
we add a helper to get attributes

	static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)
	{
		return xa_to_value(xa_load(&kvm->mem_attr_array, gfn));
	}

and then we can do


		if (KVM_BUG_ON(gfn != xas.xa_index, kvm) ||
		    attrs != kvm_get_memory_attributes(kvm, gfn)) {
			mixed = true;
			break;
		}

and

		if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
		    attrs != kvm_get_memory_attributes(kvm, gfn))
			return true;


> +
> +	return true;
> +}
> +
> +static bool mem_attrs_mixed_2m(struct kvm *kvm, unsigned long attrs,
> +			       gfn_t start, gfn_t end)
> +{
> +	XA_STATE(xas, &kvm->mem_attr_array, start);
> +	gfn_t gfn = start;
> +	void *entry;
> +	bool mixed = false;
> +
> +	rcu_read_lock();
> +	entry = xas_load(&xas);
> +	while (gfn < end) {
> +		if (xas_retry(&xas, entry))
> +			continue;
> +
> +		KVM_BUG_ON(gfn != xas.xa_index, kvm);

As above, I think it's worth bailing immediately if there's a mismatch.

> +
> +		if (!is_expected_attr_entry(entry, attrs)) {
> +			mixed = true;
> +			break;
> +		}
> +
> +		entry = xas_next(&xas);
> +		gfn++;
> +	}
> +
> +	rcu_read_unlock();
> +	return mixed;
> +}
> +
> +static bool mem_attrs_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,

s/mem_attrs_mixed/has_mixed_attrs to make it clear this is querying, not setting.
And has_mixed_attrs_2m() above.

> +			    int level, unsigned long attrs,
> +			    gfn_t start, gfn_t end)
> +{
> +	unsigned long gfn;
> +
> +	if (level == PG_LEVEL_2M)
> +		return mem_attrs_mixed_2m(kvm, attrs, start, end);
> +
> +	for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1))

Curly braces needed on the for-loop.

> +		if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)) ||
> +		    !is_expected_attr_entry(xa_load(&kvm->mem_attr_array, gfn),
> +					    attrs))
> +			return true;
> +	return false;
> +}
> +
> +static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
> +						  struct kvm_memory_slot *slot,
> +						  unsigned long attrs,
> +						  gfn_t start, gfn_t end)
> +{
> +	unsigned long pages, mask;
> +	gfn_t gfn, gfn_end, first, last;
> +	int level;
> +	bool mixed;
> +
> +	/*
> +	 * The sequence matters here: we set the higher level basing on the
> +	 * lower level's scanning result.
> +	 */
> +	for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> +		pages = KVM_PAGES_PER_HPAGE(level);
> +		mask = ~(pages - 1);
> +		first = start & mask;
> +		last = (end - 1) & mask;
> +
> +		/*
> +		 * We only need to scan the head and tail page, for middle pages
> +		 * we know they will not be mixed.
> +		 */
> +		gfn = max(first, slot->base_gfn);
> +		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
> +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> +		linfo_set_mixed(gfn, slot, level, mixed);
> +
> +		if (first == last)
> +			return;
> +
> +		for (gfn = first + pages; gfn < last; gfn += pages)
> +			linfo_set_mixed(gfn, slot, level, false);
> +
> +		gfn = last;
> +		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
> +		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> +		linfo_set_mixed(gfn, slot, level, mixed);
> +	}
> +}
> +
> +void kvm_arch_set_memory_attributes(struct kvm *kvm,
> +				    struct kvm_memory_slot *slot,
> +				    unsigned long attrs,
> +				    gfn_t start, gfn_t end)
> +{
> +	if (kvm_slot_can_be_private(slot))

Make this an early return optimization, with a comment explaining that KVM x86
doesn't yet support other attributes.

	/*
	 * KVM x86 currently only supports KVM_MEMORY_ATTRIBUTE_PRIVATE, skip
	 * the slot if the slot will never consume the PRIVATE attribute.
	 */
	if (!kvm_slot_can_be_private(slot))
		return;


> +		kvm_update_lpage_private_shared_mixed(kvm, slot, attrs,
> +						      start, end);
> +}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a07380f8d3c..5aefcff614d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
>  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
>  			linfo[lpages - 1].disallow_lpage = 1;
>  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> +		if (kvm_slot_can_be_private(slot))
> +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;

I would rather reject memslot if the gfn has lesser alignment than the offset.
I'm totally ok with this approach _if_ there's a use case.  Until such a use case
presents itself, I would rather be conservative from a uAPI perspective.

>  		/*
>  		 * If the gfn and userspace address are not aligned wrt each
>  		 * other, disable large page support for this slot.
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3331c0c92838..25099c94e770 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -592,6 +592,11 @@ struct kvm_memory_slot {
>  	struct restrictedmem_notifier notifier;
>  };
>  
> +static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
> +{
> +	return slot && (slot->flags & KVM_MEM_PRIVATE);

KVM_MEM_PRIVATE should really be defined only when private memory is exposed to
userspace.  For this patch, even though it means we have untestable code, I think
it makes sense to "return false".

> +}
> +
>  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
>  {
>  	return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
> @@ -2316,4 +2321,18 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
>  /* Max number of entries allowed for each kvm dirty ring */
>  #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
>  
> +#ifdef __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES
> +void kvm_arch_set_memory_attributes(struct kvm *kvm,
> +				    struct kvm_memory_slot *slot,
> +				    unsigned long attrs,
> +				    gfn_t start, gfn_t end);
> +#else
> +static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> +						  struct kvm_memory_slot *slot,
> +						  unsigned long attrs,
> +						  gfn_t start, gfn_t end)
> +{
> +}
> +#endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */

As above, no stub is necessary.

>  #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4e1e1e113bf0..e107afea32f0 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2354,7 +2354,8 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>  	return 0;
>  }
>  
> -static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)

Feedback for an earlier patch (to avoid churn): this should be kvm_mem_attrs_changed()
or so now that this does more than just unmap.

> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end,
> +				unsigned long attrs)

Weird nit.  I think we should keep the prototypes for kvm_mem_attrs_changed()
and kvm_arch_set_memory_attributes() somewhat similar, i.e. squeeze in @attrs
before @start.

>  {
>  	struct kvm_gfn_range gfn_range;
>  	struct kvm_memory_slot *slot;
> @@ -2378,6 +2379,10 @@ static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
>  			gfn_range.slot = slot;
>  
>  			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> +
> +			kvm_arch_set_memory_attributes(kvm, slot, attrs,
> +						       gfn_range.start,
> +						       gfn_range.end);
>  		}
>  	}
>  
> @@ -2427,7 +2432,7 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  		idx = srcu_read_lock(&kvm->srcu);
>  		KVM_MMU_LOCK(kvm);
>  		if (i > start)
> -			kvm_unmap_mem_range(kvm, start, i);
> +			kvm_unmap_mem_range(kvm, start, i, attrs->attributes);
>  		kvm_mmu_invalidate_end(kvm);
>  		KVM_MMU_UNLOCK(kvm);
>  		srcu_read_unlock(&kvm->srcu, idx);
> -- 
> 2.25.1
> 

Re: [PATCH v10 4/9] KVM: Add KVM_EXIT_MEMORY_FAULT exit

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 99352170c130..d9edb14ce30b 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6634,6 +6634,28 @@ array field represents return values. The userspace should update the return
>  values of SBI call before resuming the VCPU. For more details on RISC-V SBI
>  spec refer, https://github.com/riscv/riscv-sbi-doc.
>  
> +::
> +
> +		/* KVM_EXIT_MEMORY_FAULT */
> +		struct {
> +  #define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1ULL << 0)

Unless there's a reason not to, we should use bit 3 to match the attributes.

Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a07380f8d3c..5aefcff614d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
>  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
>  			linfo[lpages - 1].disallow_lpage = 1;
>  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> +		if (kvm_slot_can_be_private(slot))
> +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
>  		/*
>  		 * If the gfn and userspace address are not aligned wrt each
>  		 * other, disable large page support for this slot.

Forgot to talk about the bug.  This code needs to handle the scenario where a
memslot is created with existing, non-uniform attributes.  It might be a bit ugly
(I didn't even try to write the code), but it's definitely possible, and since
memslot updates are already slow I think it's best to handle things here.

In the meantime, I added this so we don't forget to fix it before merging.

#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
	pr_crit_once("FIXME: Walk the memory attributes of the slot and set the mixed status appropriately");
#endif

Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> @@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
>  			return -EIO;
>  	}
>  
> +	if (r == RET_PF_USER)
> +		return 0;
> +
>  	if (r < 0)
>  		return r;
>  	if (r != RET_PF_EMULATE)
> @@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>  		 */
>  		if (sp->role.direct &&
>  		    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> -							       PG_LEVEL_NUM)) {
> +							       PG_LEVEL_NUM,
> +							       false)) {

Passing %false is incorrect.  It might not cause problems because KVM currently
doesn't allowing modifying private memslots (that likely needs to change to allow
dirty logging), but it's wrong since nothing guarantees KVM is operating on SPTEs
for shared memory.

One option would be to take the patches from the TDX series that add a "private"
flag to the shadow page role, but I'd rather not add the role until it's truly
necessary.

For now, I think we can do this without impacting performance of guests that don't
support private memory.

int kvm_mmu_max_mapping_level(struct kvm *kvm,
			      const struct kvm_memory_slot *slot, gfn_t gfn,
			      int max_level)
{
	bool is_private = kvm_slot_can_be_private(slot) &&
			  kvm_mem_is_private(kvm, gfn);

	return __kvm_mmu_max_mapping_level(kvm, slot, gfn, max_level, is_private);
}

> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 25099c94e770..153842bb33df 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
>  }
>  #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
>  
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{

This code, i.e. the generic KVM changes, belongs in a separate patch.  It'll be
small, but I want to separate x86's page fault changes from the restrictedmem
support adding to common KVM.

This should also short-circuit based on CONFIG_HAVE_KVM_RESTRICTED_MEM, though
I would name that CONFIG_KVM_PRIVATE_MEMORY since in KVM's world, it's all about
private vs. shared at this time.

> +	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> +	       KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +}
> +#else
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{
> +	return false;
> +}
> +
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +
> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> +{
> +	int ret;
> +	struct page *page;
> +	pgoff_t index = gfn - slot->base_gfn +
> +			(slot->restricted_offset >> PAGE_SHIFT);
> +
> +	ret = restrictedmem_get_page(slot->restricted_file, index,
> +				     &page, order);

This needs handle errors.  If "ret" is non-zero, "page" is garbage.

> +	*pfn = page_to_pfn(page);
> +	return ret;
> +}
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
>  #endif
> -- 
> 2.25.1
> 

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
>  			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> +
> +		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> +			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;

Synthesizing triple fault shutdown is not the right approach.  Even with TDX's
MCE "architecture" (heavy sarcasm), it's possible that host userspace and the
guest have a paravirt interface for handling memory errors without killing the
host.

> +			r = 0;
> +			goto out;
> +		}
>  	}


> @@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
>  			mem->memory_size))
>  		return -EINVAL;
> +	if (mem->flags & KVM_MEM_PRIVATE &&
> +		(mem->restricted_offset & (PAGE_SIZE - 1) ||

Align indentation.

> +		 mem->restricted_offset > U64_MAX - mem->memory_size))

Strongly prefer to use similar logic to existing code that detects wraps:

		mem->restricted_offset + mem->memory_size < mem->restricted_offset

This is also where I'd like to add the "gfn is aligned to offset" check, though
my brain is too fried to figure that out right now.

> +		return -EINVAL;
>  	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
>  		return -EINVAL;
>  	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
>  			return -EINVAL;
>  	} else { /* Modify an existing slot. */
> +		/* Private memslots are immutable, they can only be deleted. */

I'm 99% certain I suggested this, but if we're going to make these memslots
immutable, then we should straight up disallow dirty logging, otherwise we'll
end up with a bizarre uAPI.

> +		if (mem->flags & KVM_MEM_PRIVATE)
> +			return -EINVAL;
>  		if ((mem->userspace_addr != old->userspace_addr) ||
>  		    (npages != old->npages) ||
>  		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  	new->npages = npages;
>  	new->flags = mem->flags;
>  	new->userspace_addr = mem->userspace_addr;
> +	if (mem->flags & KVM_MEM_PRIVATE) {
> +		new->restricted_file = fget(mem->restricted_fd);
> +		if (!new->restricted_file ||
> +		    !file_is_restrictedmem(new->restricted_file)) {
> +			r = -EINVAL;
> +			goto out;
> +		}
> +		new->restricted_offset = mem->restricted_offset;
> +	}
> +
> +	new->kvm = kvm;

Set this above, just so that the code flows better.

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Fri, Dec 02, 2022, Chao Peng wrote:
> This patch series implements KVM guest private memory for confidential
> computing scenarios like Intel TDX[1]. If a TDX host accesses
> TDX-protected guest memory, machine check can happen which can further
> crash the running host system, this is terrible for multi-tenant
> configurations. The host accesses include those from KVM userspace like
> QEMU. This series addresses KVM userspace induced crash by introducing
> new mm and KVM interfaces so KVM userspace can still manage guest memory
> via a fd-based approach, but it can never access the guest memory
> content.
> 
> The patch series touches both core mm and KVM code. I appreciate
> Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> reviews are always welcome.
>   - 01: mm change, target for mm tree
>   - 02-09: KVM change, target for KVM tree

A version with all of my feedback, plus reworked versions of Vishal's selftest,
is available here:

  git@github.com:sean-jc/linux.git x86/upm_base_support

It compiles and passes the selftest, but it's otherwise barely tested.  There are
a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
a WIP.

As for next steps, can you (handwaving all of the TDX folks) take a look at what
I pushed and see if there's anything horrifically broken, and that it still works
for TDX?

Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
(and I mean that).

On my side, the two things on my mind are (a) tests and (b) downstream dependencies
(SEV and TDX).  For tests, I want to build a lists of tests that are required for
merging so that the criteria for merging are clear, and so that if the list is large
(haven't thought much yet), the work of writing and running tests can be distributed.

Regarding downstream dependencies, before this lands, I want to pull in all the
TDX and SNP series and see how everything fits together.  Specifically, I want to
make sure that we don't end up with a uAPI that necessitates ugly code, and that we
don't miss an opportunity to make things simpler.  The patches in the SNP series to
add "legacy" SEV support for UPM in particular made me slightly rethink some minor
details.  Nothing remotely major, but something that needs attention since it'll
be uAPI.

I'm off Monday, so it'll be at least Tuesday before I make any more progress on
my side.

Thanks!

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Kirill A. Shutemov]

On Sat, Jan 14, 2023 at 12:37:59AM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
> > This patch series implements KVM guest private memory for confidential
> > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > TDX-protected guest memory, machine check can happen which can further
> > crash the running host system, this is terrible for multi-tenant
> > configurations. The host accesses include those from KVM userspace like
> > QEMU. This series addresses KVM userspace induced crash by introducing
> > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > via a fd-based approach, but it can never access the guest memory
> > content.
> > 
> > The patch series touches both core mm and KVM code. I appreciate
> > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > reviews are always welcome.
> >   - 01: mm change, target for mm tree
> >   - 02-09: KVM change, target for KVM tree
> 
> A version with all of my feedback, plus reworked versions of Vishal's selftest,
> is available here:
> 
>   git@github.com:sean-jc/linux.git x86/upm_base_support
> 
> It compiles and passes the selftest, but it's otherwise barely tested.  There are
> a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> a WIP.
> 
> As for next steps, can you (handwaving all of the TDX folks) take a look at what
> I pushed and see if there's anything horrifically broken, and that it still works
> for TDX?

Minor build fix:

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6eb5336ccc65..4a9e9fa2552a 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7211,8 +7211,8 @@ void kvm_arch_set_memory_attributes(struct kvm *kvm,
 	int level;
 	bool mixed;
 
-	lockdep_assert_held_write(kvm->mmu_lock);
-	lockdep_assert_held(kvm->slots_lock);
+	lockdep_assert_held_write(&kvm->mmu_lock);
+	lockdep_assert_held(&kvm->slots_lock);
 
 	/*
 	 * KVM x86 currently only supports KVM_MEMORY_ATTRIBUTE_PRIVATE, skip
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 467916943c73..4ef60ba7eb1d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2304,7 +2304,7 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
 static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)
 {
-	lockdep_assert_held(kvm->mmu_lock);
+	lockdep_assert_held(&kvm->mmu_lock);
 
 	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn));
 }
-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Binbin Wu]

On 12/2/2022 2:13 PM, Chao Peng wrote:
> In confidential computing usages, whether a page is private or shared is
> necessary information for KVM to perform operations like page fault
> handling, page zapping etc. There are other potential use cases for
> per-page memory attributes, e.g. to make memory read-only (or no-exec,
> or exec-only, etc.) without having to modify memslots.
>
> Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> userspace to operate on the per-page memory attributes.
>    - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
>      a guest memory range.
>    - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
>      memory attributes.
>
> KVM internally uses xarray to store the per-page memory attributes.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> ---
>   Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
>   arch/x86/kvm/Kconfig           |  1 +
>   include/linux/kvm_host.h       |  3 ++
>   include/uapi/linux/kvm.h       | 17 ++++++++

Should the changes introduced in this file also need to be added in 
tools/include/uapi/linux/kvm.h ?



>   virt/kvm/Kconfig               |  3 ++
>   virt/kvm/kvm_main.c            | 76 ++++++++++++++++++++++++++++++++++
>   6 files changed, 163 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 5617bc4f899f..bb2f709c0900 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct.
>   The "pad" and "reserved" fields may be used for future extensions and should be
>   set to 0s by userspace.
>   
> +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: u64 memory attributes bitmask(out)
> +:Returns: 0 on success, <0 on error
> +
> +Returns supported memory attributes bitmask. Supported memory attributes will
> +have the corresponding bits set in u64 memory attributes bitmask.
> +
> +The following memory attributes are defined::
> +
> +  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> +
> +4.139 KVM_SET_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: struct kvm_memory_attributes(in/out)
> +:Returns: 0 on success, <0 on error
> +
> +Sets memory attributes for pages in a guest memory range. Parameters are
> +specified via the following structure::
> +
> +  struct kvm_memory_attributes {
> +	__u64 address;
> +	__u64 size;
> +	__u64 attributes;
> +	__u64 flags;
> +  };
> +
> +The user sets the per-page memory attributes to a guest memory range indicated
> +by address/size, and in return KVM adjusts address and size to reflect the
> +actual pages of the memory range have been successfully set to the attributes.
> +If the call returns 0, "address" is updated to the last successful address + 1
> +and "size" is updated to the remaining address size that has not been set
> +successfully. The user should check the return value as well as the size to
> +decide if the operation succeeded for the whole range or not. The user may want
> +to retry the operation with the returned address/size if the previous range was
> +partially successful.
> +
> +Both address and size should be page aligned and the supported attributes can be
> +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> +
> +The "flags" field may be used for future extensions and should be set to 0s.
> +
>   5. The kvm_run structure
>   ========================
>   
> @@ -8270,6 +8323,16 @@ structure.
>   When getting the Modified Change Topology Report value, the attr->addr
>   must point to a byte where the value will be stored or retrieved from.
>   
> +8.40 KVM_CAP_MEMORY_ATTRIBUTES
> +------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm
> +
> +This capability indicates KVM supports per-page memory attributes and ioctls
> +KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available.
> +
>   9. Known KVM API problems
>   =========================
>   
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index fbeaa9ddef59..a8e379a3afee 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -49,6 +49,7 @@ config KVM
>   	select SRCU
>   	select INTERVAL_TREE
>   	select HAVE_KVM_PM_NOTIFIER if PM
> +	select HAVE_KVM_MEMORY_ATTRIBUTES
>   	help
>   	  Support hosting fully virtualized guest machines using hardware
>   	  virtualization extensions.  You will need a fairly recent
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8f874a964313..a784e2b06625 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -800,6 +800,9 @@ struct kvm {
>   
>   #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
>   	struct notifier_block pm_notifier;
> +#endif
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	struct xarray mem_attr_array;
>   #endif
>   	char stats_id[KVM_STATS_NAME_SIZE];
>   };
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 64dfe9c07c87..5d0941acb5bb 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1182,6 +1182,7 @@ struct kvm_ppc_resize_hpt {
>   #define KVM_CAP_S390_CPU_TOPOLOGY 222
>   #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
>   #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
> +#define KVM_CAP_MEMORY_ATTRIBUTES 225
>   
>   #ifdef KVM_CAP_IRQ_ROUTING
>   
> @@ -2238,4 +2239,20 @@ struct kvm_s390_zpci_op {
>   /* flags for kvm_s390_zpci_op->u.reg_aen.flags */
>   #define KVM_S390_ZPCIOP_REGAEN_HOST    (1 << 0)
>   
> +/* Available with KVM_CAP_MEMORY_ATTRIBUTES */
> +#define KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES    _IOR(KVMIO,  0xd2, __u64)
> +#define KVM_SET_MEMORY_ATTRIBUTES              _IOWR(KVMIO,  0xd3, struct kvm_memory_attributes)
> +
> +struct kvm_memory_attributes {
> +	__u64 address;
> +	__u64 size;
> +	__u64 attributes;
> +	__u64 flags;
> +};
> +
> +#define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +#define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +#define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +#define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> +
>   #endif /* __LINUX_KVM_H */
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 800f9470e36b..effdea5dd4f0 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -19,6 +19,9 @@ config HAVE_KVM_IRQ_ROUTING
>   config HAVE_KVM_DIRTY_RING
>          bool
>   
> +config HAVE_KVM_MEMORY_ATTRIBUTES
> +       bool
> +
>   # Only strongly ordered architectures can select this, as it doesn't
>   # put any explicit constraint on userspace ordering. They can also
>   # select the _ACQ_REL version.
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1782c4555d94..7f0f5e9f2406 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>   	spin_lock_init(&kvm->mn_invalidate_lock);
>   	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
>   	xa_init(&kvm->vcpu_array);
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	xa_init(&kvm->mem_attr_array);
> +#endif
>   
>   	INIT_LIST_HEAD(&kvm->gpc_list);
>   	spin_lock_init(&kvm->gpc_lock);
> @@ -1323,6 +1326,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
>   		kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
>   		kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
>   	}
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	xa_destroy(&kvm->mem_attr_array);
> +#endif
>   	cleanup_srcu_struct(&kvm->irq_srcu);
>   	cleanup_srcu_struct(&kvm->srcu);
>   	kvm_arch_free_vm(kvm);
> @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
>   }
>   #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
>   
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> +{
> +	return 0;
> +}
> +
> +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> +					   struct kvm_memory_attributes *attrs)
> +{
> +	gfn_t start, end;
> +	unsigned long i;
> +	void *entry;
> +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> +
> +	/* flags is currently not used. */
> +	if (attrs->flags)
> +		return -EINVAL;
> +	if (attrs->attributes & ~supported_attrs)
> +		return -EINVAL;
> +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> +		return -EINVAL;
> +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> +		return -EINVAL;
> +
> +	start = attrs->address >> PAGE_SHIFT;
> +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> +
> +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> +
> +	mutex_lock(&kvm->lock);
> +	for (i = start; i < end; i++)
> +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> +				    GFP_KERNEL_ACCOUNT)))
> +			break;
> +	mutex_unlock(&kvm->lock);
> +
> +	attrs->address = i << PAGE_SHIFT;
> +	attrs->size = (end - i) << PAGE_SHIFT;
> +
> +	return 0;
> +}
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +
>   struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
>   {
>   	return __gfn_to_memslot(kvm_memslots(kvm), gfn);
> @@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>   #ifdef CONFIG_HAVE_KVM_MSI
>   	case KVM_CAP_SIGNAL_MSI:
>   #endif
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	case KVM_CAP_MEMORY_ATTRIBUTES:
> +#endif
>   #ifdef CONFIG_HAVE_KVM_IRQFD
>   	case KVM_CAP_IRQFD:
>   	case KVM_CAP_IRQFD_RESAMPLE:
> @@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp,
>   		break;
>   	}
>   #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
> +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> +	case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: {
> +		u64 attrs = kvm_supported_mem_attributes(kvm);
> +
> +		r = -EFAULT;
> +		if (copy_to_user(argp, &attrs, sizeof(attrs)))
> +			goto out;
> +		r = 0;
> +		break;
> +	}
> +	case KVM_SET_MEMORY_ATTRIBUTES: {
> +		struct kvm_memory_attributes attrs;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&attrs, argp, sizeof(attrs)))
> +			goto out;
> +
> +		r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);
> +
> +		if (!r && copy_to_user(argp, &attrs, sizeof(attrs)))
> +			r = -EFAULT;
> +		break;
> +	}
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
>   	case KVM_CREATE_DEVICE: {
>   		struct kvm_create_device cd;
>   

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Fri, Jan 13, 2023 at 09:54:41PM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
> > The system call is currently wired up for x86 arch.
> 
> Building on other architectures (except for arm64 for some reason) yields:
> 
>   CALL    /.../scripts/checksyscalls.sh
>   <stdin>:1565:2: warning: #warning syscall memfd_restricted not implemented [-Wcpp]
> 
> Do we care?  It's the only such warning, which makes me think we either need to
> wire this up for all architectures, or explicitly document that it's unsupported.

I'm a bit conservative and prefer enabling only on x86 where we know the
exact usecase. For the warning we can get rid of by changing
scripts/checksyscalls.sh, just like __IGNORE_memfd_secret:

https://lkml.kernel.org/r/20210518072034.31572-7-rppt@kernel.org

> 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> 
> ...
> 
> > diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
> > new file mode 100644
> > index 000000000000..c2700c5daa43
> > --- /dev/null
> > +++ b/include/linux/restrictedmem.h
> > @@ -0,0 +1,71 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +#ifndef _LINUX_RESTRICTEDMEM_H
> 
> Missing
> 
>  #define _LINUX_RESTRICTEDMEM_H
> 
> which causes fireworks if restrictedmem.h is included more than once.
> 
> > +#include <linux/file.h>
> > +#include <linux/magic.h>
> > +#include <linux/pfn_t.h>
> 
> ...
> 
> > +static inline int restrictedmem_get_page(struct file *file, pgoff_t offset,
> > +					 struct page **pagep, int *order)
> > +{
> > +	return -1;
> 
> This should be a proper -errno, though in the current incarnation of things it's
> a moot point because no stub is needed.  KVM can (and should) easily provide its
> own stub for this one.
> 
> > +}
> > +
> > +static inline bool file_is_restrictedmem(struct file *file)
> > +{
> > +	return false;
> > +}
> > +
> > +static inline void restrictedmem_error_page(struct page *page,
> > +					    struct address_space *mapping)
> > +{
> > +}
> > +
> > +#endif /* CONFIG_RESTRICTEDMEM */
> > +
> > +#endif /* _LINUX_RESTRICTEDMEM_H */
> 
> ...
> 
> > diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> > new file mode 100644
> > index 000000000000..56953c204e5c
> > --- /dev/null
> > +++ b/mm/restrictedmem.c
> > @@ -0,0 +1,318 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "linux/sbitmap.h"
> > +#include <linux/pagemap.h>
> > +#include <linux/pseudo_fs.h>
> > +#include <linux/shmem_fs.h>
> > +#include <linux/syscalls.h>
> > +#include <uapi/linux/falloc.h>
> > +#include <uapi/linux/magic.h>
> > +#include <linux/restrictedmem.h>
> > +
> > +struct restrictedmem_data {
> 
> Any objection to simply calling this "restrictedmem"?  And then using either "rm"
> or "rmem" for local variable names?  I kept reading "data" as the underyling data
> being written to the page, as opposed to the metadata describing the restrictedmem
> instance.
> 
> > +	struct mutex lock;
> > +	struct file *memfd;
> > +	struct list_head notifiers;
> > +};
> > +
> > +static void restrictedmem_invalidate_start(struct restrictedmem_data *data,
> > +					   pgoff_t start, pgoff_t end)
> > +{
> > +	struct restrictedmem_notifier *notifier;
> > +
> > +	mutex_lock(&data->lock);
> 
> This can be a r/w semaphore instead of a mutex, that way punching holes at multiple
> points in the file can at least run the notifiers in parallel.  The actual allocation
> by shmem will still be serialized, but I think it's worth the simple optimization
> since zapping and flushing in KVM may be somewhat slow.
> 
> > +	list_for_each_entry(notifier, &data->notifiers, list) {
> > +		notifier->ops->invalidate_start(notifier, start, end);
> 
> Two major design issues that we overlooked long ago:
> 
>   1. Blindly invoking notifiers will not scale.  E.g. if userspace configures a
>      VM with a large number of convertible memslots that are all backed by a
>      single large restrictedmem instance, then converting a single page will
>      result in a linear walk through all memslots.  I don't expect anyone to
>      actually do something silly like that, but I also never expected there to be
>      a legitimate usecase for thousands of memslots.
> 
>   2. This approach fails to provide the ability for KVM to ensure a guest has
>      exclusive access to a page.  As discussed in the past, the kernel can rely
>      on hardware (and maybe ARM's pKVM implementation?) for those guarantees, but
>      only for SNP and TDX VMs.  For VMs where userspace is trusted to some extent,
>      e.g. SEV, there is value in ensuring a 1:1 association.
> 
>      And probably more importantly, relying on hardware for SNP and TDX yields a
>      poor ABI and complicates KVM's internals.  If the kernel doesn't guarantee a
>      page is exclusive to a guest, i.e. if userspace can hand out the same page
>      from a restrictedmem instance to multiple VMs, then failure will occur only
>      when KVM tries to assign the page to the second VM.  That will happen deep
>      in KVM, which means KVM needs to gracefully handle such errors, and it means
>      that KVM's ABI effectively allows plumbing garbage into its memslots.

It may not be a valid usage, but in my TDX environment I do meet below
issue.

kvm_set_user_memory AddrSpace#0 Slot#0 flags=0x4 gpa=0x0 size=0x80000000 ua=0x7fe1ebfff000 ret=0
kvm_set_user_memory AddrSpace#0 Slot#1 flags=0x4 gpa=0xffc00000 size=0x400000 ua=0x7fe271579000 ret=0
kvm_set_user_memory AddrSpace#0 Slot#2 flags=0x4 gpa=0xfeda0000 size=0x20000 ua=0x7fe1ec09f000 ret=-22

Slot#2('SMRAM') is actually an alias into system memory(Slot#0) in QEMU
and slot#2 fails due to below exclusive check.

Currently I changed QEMU code to mark these alias slots as shared
instead of private but I'm not 100% confident this is correct fix.

> 
> Rather than use a simple list of notifiers, this appears to be yet another
> opportunity to use an xarray.  Supporting sharing of restrictedmem will be
> non-trivial, but IMO we should punt that to the future since it's still unclear
> exactly how sharing will work.
> 
> An xarray will solve #1 by notifying only the consumers (memslots) that are bound
> to the affected range.
> 
> And for #2, it's relatively straightforward (knock wood) to detect existing
> entries, i.e. if the user wants exclusive access to memory, then the bind operation
> can be reject if there's an existing entry.
> 
> VERY lightly tested code snippet at the bottom (will provide link to fully worked
> code in cover letter).
> 
> 
> > +static long restrictedmem_punch_hole(struct restrictedmem_data *data, int mode,
> > +				     loff_t offset, loff_t len)
> > +{
> > +	int ret;
> > +	pgoff_t start, end;
> > +	struct file *memfd = data->memfd;
> > +
> > +	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> > +		return -EINVAL;
> > +
> > +	start = offset >> PAGE_SHIFT;
> > +	end = (offset + len) >> PAGE_SHIFT;
> > +
> > +	restrictedmem_invalidate_start(data, start, end);
> > +	ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> > +	restrictedmem_invalidate_end(data, start, end);
> 
> The lock needs to be end for the entire duration of the hole punch, i.e. needs to
> be taken before invalidate_start() and released after invalidate_end().  If a user
> (un)binds/(un)registers after invalidate_state(), it will see an unpaired notification,
> e.g. could leave KVM with incorrect notifier counts.
> 
> > +
> > +	return ret;
> > +}
> 
> What I ended up with for an xarray-based implementation.  I'm very flexible on
> names and whatnot, these are just what made sense to me.
> 
> static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
> 				     loff_t offset, loff_t len)
> {
> 	struct restrictedmem_notifier *notifier;
> 	struct file *memfd = rm->memfd;
> 	unsigned long index;
> 	pgoff_t start, end;
> 	int ret;
> 
> 	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> 		return -EINVAL;
> 
> 	start = offset >> PAGE_SHIFT;
> 	end = (offset + len) >> PAGE_SHIFT;
> 
> 	/*
> 	 * Bindings must stable across invalidation to ensure the start+end
> 	 * are balanced.
> 	 */
> 	down_read(&rm->lock);
> 
> 	xa_for_each_range(&rm->bindings, index, notifier, start, end)
> 		notifier->ops->invalidate_start(notifier, start, end);
> 
> 	ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> 
> 	xa_for_each_range(&rm->bindings, index, notifier, start, end)
> 		notifier->ops->invalidate_end(notifier, start, end);
> 
> 	up_read(&rm->lock);
> 
> 	return ret;
> }
> 
> int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
> 		       struct restrictedmem_notifier *notifier, bool exclusive)
> {
> 	struct restrictedmem *rm = file->f_mapping->private_data;
> 	int ret = -EINVAL;
> 
> 	down_write(&rm->lock);
> 
> 	/* Non-exclusive mappings are not yet implemented. */
> 	if (!exclusive)
> 		goto out_unlock;
> 
> 	if (!xa_empty(&rm->bindings)) {
> 		if (exclusive != rm->exclusive)
> 			goto out_unlock;
> 
> 		if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
> 			goto out_unlock;
> 	}
> 
> 	xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);
> 	rm->exclusive = exclusive;
> 	ret = 0;
> out_unlock:
> 	up_write(&rm->lock);
> 	return ret;
> }
> EXPORT_SYMBOL_GPL(restrictedmem_bind);
> 
> void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
> 			  struct restrictedmem_notifier *notifier)
> {
> 	struct restrictedmem *rm = file->f_mapping->private_data;
> 
> 	down_write(&rm->lock);
> 	xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
> 	synchronize_rcu();
> 	up_write(&rm->lock);
> }
> EXPORT_SYMBOL_GPL(restrictedmem_unbind);

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Chao Peng]

On Fri, Jan 13, 2023 at 10:37:39PM +0000, Sean Christopherson wrote:
> On Tue, Jan 10, 2023, Chao Peng wrote:
> > On Mon, Jan 09, 2023 at 07:32:05PM +0000, Sean Christopherson wrote:
> > > On Fri, Jan 06, 2023, Chao Peng wrote:
> > > > On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote:
> > > > > On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > > > > > To make future maintenance easy, internally use a binary compatible
> > > > > > alias struct kvm_user_mem_region to handle both the normal and the
> > > > > > '_ext' variants.
> > > > > 
> > > > > Feels bit hacky IMHO, and more like a completely new feature than
> > > > > an extension.
> > > > > 
> > > > > Why not just add a new ioctl? The commit message does not address
> > > > > the most essential design here.
> > > > 
> > > > Yes, people can always choose to add a new ioctl for this kind of change
> > > > and the balance point here is we want to also avoid 'too many ioctls' if
> > > > the functionalities are similar.  The '_ext' variant reuses all the
> > > > existing fields in the 'normal' variant and most importantly KVM
> > > > internally can reuse most of the code. I certainly can add some words in
> > > > the commit message to explain this design choice.
> > > 
> > > After seeing the userspace side of this, I agree with Jarkko; overloading
> > > KVM_SET_USER_MEMORY_REGION is a hack.  E.g. the size validation ends up being
> > > bogus, and userspace ends up abusing unions or implementing kvm_user_mem_region
> > > itself.
> > 
> > How is the size validation being bogus? I don't quite follow.
> 
> The ioctl() magic embeds the size of the payload (struct kvm_userspace_memory_region
> in this case) in the ioctl() number, and that information is visible to userspace
> via _IOCTL_SIZE().  Attempting to take a larger size can mess up sanity checks,
> e.g. KVM selftests get tripped up on this assert if KVM_SET_USER_MEMORY_REGION is
> passed an "extended" struct.
> 
> 	#define kvm_do_ioctl(fd, cmd, arg)						\
> 	({										\
> 		kvm_static_assert(!_IOC_SIZE(cmd) || sizeof(*arg) == _IOC_SIZE(cmd));	\
> 		ioctl(fd, cmd, arg);							\
> 	})

Got it. Thanks for the explanation.

Chao

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
> > @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> >  
> >  		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
> >  			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> > +
> > +		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> > +			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> 
> Synthesizing triple fault shutdown is not the right approach.  Even with TDX's
> MCE "architecture" (heavy sarcasm), it's possible that host userspace and the
> guest have a paravirt interface for handling memory errors without killing the
> host.

Agree shutdown is not the correct choice. I see you made below change:

send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva, PAGE_SHIFT, current)

The MCE may happen in any thread than KVM thread, sending siginal to
'current' thread may not be the expected behavior. Also how userspace
can tell is the MCE on the shared page or private page? Do we care?

> 
> > +			r = 0;
> > +			goto out;
> > +		}
> >  	}
> 
> 
> > @@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >  	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
> >  			mem->memory_size))
> >  		return -EINVAL;
> > +	if (mem->flags & KVM_MEM_PRIVATE &&
> > +		(mem->restricted_offset & (PAGE_SIZE - 1) ||
> 
> Align indentation.
> 
> > +		 mem->restricted_offset > U64_MAX - mem->memory_size))
> 
> Strongly prefer to use similar logic to existing code that detects wraps:
> 
> 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
> 
> This is also where I'd like to add the "gfn is aligned to offset" check, though
> my brain is too fried to figure that out right now.
> 
> > +		return -EINVAL;
> >  	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> >  		return -EINVAL;
> >  	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> > @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >  		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
> >  			return -EINVAL;
> >  	} else { /* Modify an existing slot. */
> > +		/* Private memslots are immutable, they can only be deleted. */
> 
> I'm 99% certain I suggested this, but if we're going to make these memslots
> immutable, then we should straight up disallow dirty logging, otherwise we'll
> end up with a bizarre uAPI.

But in my mind dirty logging will be needed in the very short time, when
live migration gets supported?

> 
> > +		if (mem->flags & KVM_MEM_PRIVATE)
> > +			return -EINVAL;
> >  		if ((mem->userspace_addr != old->userspace_addr) ||
> >  		    (npages != old->npages) ||
> >  		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> > @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >  	new->npages = npages;
> >  	new->flags = mem->flags;
> >  	new->userspace_addr = mem->userspace_addr;
> > +	if (mem->flags & KVM_MEM_PRIVATE) {
> > +		new->restricted_file = fget(mem->restricted_fd);
> > +		if (!new->restricted_file ||
> > +		    !file_is_restrictedmem(new->restricted_file)) {
> > +			r = -EINVAL;
> > +			goto out;
> > +		}
> > +		new->restricted_offset = mem->restricted_offset;

I see you changed slot->restricted_offset type from loff_t to gfn_t and
used pgoff_t when doing the restrictedmem_bind/unbind(). Using page
index is reasonable KVM internally and sounds simpler than loff_t. But
we also need initialize it to page index here as well as changes in
another two cases. This is needed when restricted_offset != 0.

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 547b92215002..49e375e78f30 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2364,8 +2364,7 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
                                             gfn_t gfn, kvm_pfn_t *pfn,
                                             int *order)
 {
-       pgoff_t index = gfn - slot->base_gfn +
-                       (slot->restricted_offset >> PAGE_SHIFT);
+       pgoff_t index = gfn - slot->base_gfn + slot->restricted_offset;
        struct page *page;
        int ret;
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 01db35ddd5b3..7439bdcb0d04 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -935,7 +935,7 @@ static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
                                         pgoff_t start, pgoff_t end,
                                         gfn_t *gfn_start, gfn_t *gfn_end)
 {
-       unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
+       unsigned long base_pgoff = slot->restricted_offset;
 
        if (start > base_pgoff)
                *gfn_start = slot->base_gfn + start - base_pgoff;
@@ -2275,7 +2275,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
                        r = -EINVAL;
                        goto out;
                }
-               new->restricted_offset = mem->restricted_offset;
+               new->restricted_offset = mem->restricted_offset >> PAGE_SHIFT;
        }
 
        r = kvm_set_memslot(kvm, old, new, change);

Chao
> > +	}
> > +
> > +	new->kvm = kvm;
> 
> Set this above, just so that the code flows better.

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Chao Peng]

On Sat, Jan 14, 2023 at 12:37:59AM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
> > This patch series implements KVM guest private memory for confidential
> > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > TDX-protected guest memory, machine check can happen which can further
> > crash the running host system, this is terrible for multi-tenant
> > configurations. The host accesses include those from KVM userspace like
> > QEMU. This series addresses KVM userspace induced crash by introducing
> > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > via a fd-based approach, but it can never access the guest memory
> > content.
> > 
> > The patch series touches both core mm and KVM code. I appreciate
> > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > reviews are always welcome.
> >   - 01: mm change, target for mm tree
> >   - 02-09: KVM change, target for KVM tree
> 
> A version with all of my feedback, plus reworked versions of Vishal's selftest,
> is available here:
> 
>   git@github.com:sean-jc/linux.git x86/upm_base_support
> 
> It compiles and passes the selftest, but it's otherwise barely tested.  There are
> a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> a WIP.

Thanks very much for doing this. Almost all of your comments are well
received, except for two cases that need more discussions which have
replied individually.

> 
> As for next steps, can you (handwaving all of the TDX folks) take a look at what
> I pushed and see if there's anything horrifically broken, and that it still works
> for TDX?

I have integrated this into my local TDX repo, with some changes (as I
replied individually), the new code basically still works with TDX.

I have also asked other TDX folks to take a look.

> 
> Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> (and I mean that).
> 
> On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> merging so that the criteria for merging are clear, and so that if the list is large
> (haven't thought much yet), the work of writing and running tests can be distributed.
> 
> Regarding downstream dependencies, before this lands, I want to pull in all the
> TDX and SNP series and see how everything fits together.  Specifically, I want to
> make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> don't miss an opportunity to make things simpler.  The patches in the SNP series to
> add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> details.  Nothing remotely major, but something that needs attention since it'll
> be uAPI.
> 
> I'm off Monday, so it'll be at least Tuesday before I make any more progress on
> my side.

Appreciate your effort. As for the next steps, if you see something we
can do parallel, feel free to let me know.

Thanks,
Chao

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Tue, Jan 17, 2023 at 11:21:10AM +0800, Binbin Wu wrote:
> 
> On 12/2/2022 2:13 PM, Chao Peng wrote:
> > In confidential computing usages, whether a page is private or shared is
> > necessary information for KVM to perform operations like page fault
> > handling, page zapping etc. There are other potential use cases for
> > per-page memory attributes, e.g. to make memory read-only (or no-exec,
> > or exec-only, etc.) without having to modify memslots.
> > 
> > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> > userspace to operate on the per-page memory attributes.
> >    - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
> >      a guest memory range.
> >    - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
> >      memory attributes.
> > 
> > KVM internally uses xarray to store the per-page memory attributes.
> > 
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> > ---
> >   Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
> >   arch/x86/kvm/Kconfig           |  1 +
> >   include/linux/kvm_host.h       |  3 ++
> >   include/uapi/linux/kvm.h       | 17 ++++++++
> 
> Should the changes introduced in this file also need to be added in
> tools/include/uapi/linux/kvm.h ?

Yes I think. But I'm hesitate to include in this patch or not. I see
many commits sync kernel kvm.h to tools's copy. Looks that is done
periodically and with a 'pull' model.

Chao

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Fuad Tabba]

Hi Sean,

On Sat, Jan 14, 2023 at 12:38 AM Sean Christopherson <seanjc@google.com> wrote:
>
> On Fri, Dec 02, 2022, Chao Peng wrote:
> > This patch series implements KVM guest private memory for confidential
> > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > TDX-protected guest memory, machine check can happen which can further
> > crash the running host system, this is terrible for multi-tenant
> > configurations. The host accesses include those from KVM userspace like
> > QEMU. This series addresses KVM userspace induced crash by introducing
> > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > via a fd-based approach, but it can never access the guest memory
> > content.
> >
> > The patch series touches both core mm and KVM code. I appreciate
> > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > reviews are always welcome.
> >   - 01: mm change, target for mm tree
> >   - 02-09: KVM change, target for KVM tree
>
> A version with all of my feedback, plus reworked versions of Vishal's selftest,
> is available here:
>
>   git@github.com:sean-jc/linux.git x86/upm_base_support
>
> It compiles and passes the selftest, but it's otherwise barely tested.  There are
> a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> a WIP.
>
> As for next steps, can you (handwaving all of the TDX folks) take a look at what
> I pushed and see if there's anything horrifically broken, and that it still works
> for TDX?
>
> Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> (and I mean that).

Thanks for sharing this. I've had a look at the patches, and have
ported them to work with pKVM. At a high level, the new interface
seems fine and it works with the arm64/pKVM port. I have a couple of
comments regarding some of the details, but they can wait until v11 is
posted.

Cheers,
/fuad



> On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> merging so that the criteria for merging are clear, and so that if the list is large
> (haven't thought much yet), the work of writing and running tests can be distributed.
>
> Regarding downstream dependencies, before this lands, I want to pull in all the
> TDX and SNP series and see how everything fits together.  Specifically, I want to
> make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> don't miss an opportunity to make things simpler.  The patches in the SNP series to
> add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> details.  Nothing remotely major, but something that needs attention since it'll
> be uAPI.
>
> I'm off Monday, so it'll be at least Tuesday before I make any more progress on
> my side.
>
> Thanks!

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Sean Christopherson]

On Tue, Jan 17, 2023, Chao Peng wrote:
> On Fri, Jan 13, 2023 at 09:54:41PM +0000, Sean Christopherson wrote:
> > > +	list_for_each_entry(notifier, &data->notifiers, list) {
> > > +		notifier->ops->invalidate_start(notifier, start, end);
> > 
> > Two major design issues that we overlooked long ago:
> > 
> >   1. Blindly invoking notifiers will not scale.  E.g. if userspace configures a
> >      VM with a large number of convertible memslots that are all backed by a
> >      single large restrictedmem instance, then converting a single page will
> >      result in a linear walk through all memslots.  I don't expect anyone to
> >      actually do something silly like that, but I also never expected there to be
> >      a legitimate usecase for thousands of memslots.
> > 
> >   2. This approach fails to provide the ability for KVM to ensure a guest has
> >      exclusive access to a page.  As discussed in the past, the kernel can rely
> >      on hardware (and maybe ARM's pKVM implementation?) for those guarantees, but
> >      only for SNP and TDX VMs.  For VMs where userspace is trusted to some extent,
> >      e.g. SEV, there is value in ensuring a 1:1 association.
> > 
> >      And probably more importantly, relying on hardware for SNP and TDX yields a
> >      poor ABI and complicates KVM's internals.  If the kernel doesn't guarantee a
> >      page is exclusive to a guest, i.e. if userspace can hand out the same page
> >      from a restrictedmem instance to multiple VMs, then failure will occur only
> >      when KVM tries to assign the page to the second VM.  That will happen deep
> >      in KVM, which means KVM needs to gracefully handle such errors, and it means
> >      that KVM's ABI effectively allows plumbing garbage into its memslots.
> 
> It may not be a valid usage, but in my TDX environment I do meet below
> issue.
> 
> kvm_set_user_memory AddrSpace#0 Slot#0 flags=0x4 gpa=0x0 size=0x80000000 ua=0x7fe1ebfff000 ret=0
> kvm_set_user_memory AddrSpace#0 Slot#1 flags=0x4 gpa=0xffc00000 size=0x400000 ua=0x7fe271579000 ret=0
> kvm_set_user_memory AddrSpace#0 Slot#2 flags=0x4 gpa=0xfeda0000 size=0x20000 ua=0x7fe1ec09f000 ret=-22
> 
> Slot#2('SMRAM') is actually an alias into system memory(Slot#0) in QEMU
> and slot#2 fails due to below exclusive check.
> 
> Currently I changed QEMU code to mark these alias slots as shared
> instead of private but I'm not 100% confident this is correct fix.

That's a QEMU bug of sorts.  SMM is mutually exclusive with TDX, QEMU shouldn't
be configuring SMRAM (or any SMM memslots for that matter) for TDX guests.

Actually, KVM should enforce that by disallowing SMM memslots for TDX guests.
Ditto for SNP guests and UPM-backed SEV and SEV-ES guests.  I think it probably
even makes sense to introduce that restriction in the base UPM support, e.g.
something like the below.  That would unnecessarily prevent emulating SMM for
KVM_X86_PROTECTED_VM types that aren't encrypted, but IMO that's an acceptable
limitation until there's an actual use case for KVM_X86_PROTECTED_VM guests beyond
SEV (my thought is that KVM_X86_PROTECTED_VM will mostly be a vehicle for selftests
and UPM-based SEV and SEV-ES guests).

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 48b7bdad1e0a..0a8aac821cb0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4357,6 +4357,14 @@ bool kvm_arch_has_private_mem(struct kvm *kvm)
        return kvm->arch.vm_type != KVM_X86_DEFAULT_VM;
 }
 
+bool kvm_arch_nr_address_spaces(struct kvm *kvm)
+{
+       if (kvm->arch.vm_type != KVM_X86_DEFAULT_VM)
+               return 1;
+
+       return KVM_ADDRESS_SPACE_NUM;
+}
+
 static bool kvm_is_vm_type_supported(unsigned long type)
 {
        return type == KVM_X86_DEFAULT_VM ||
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 97801d81ee42..e0a3fc819fe5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2126,7 +2126,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
             mem->restricted_offset + mem->memory_size < mem->restricted_offset ||
             0 /* TODO: require gfn be aligned with restricted offset */))
                return -EINVAL;
-       if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
+       if (as_id >= kvm_arch_nr_address_spaces(vm) || id >= KVM_MEM_SLOTS_NUM)
                return -EINVAL;
        if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
                return -EINVAL;

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Tue, Jan 17, 2023, Chao Peng wrote:
> On Tue, Jan 17, 2023 at 11:21:10AM +0800, Binbin Wu wrote:
> > 
> > On 12/2/2022 2:13 PM, Chao Peng wrote:
> > > In confidential computing usages, whether a page is private or shared is
> > > necessary information for KVM to perform operations like page fault
> > > handling, page zapping etc. There are other potential use cases for
> > > per-page memory attributes, e.g. to make memory read-only (or no-exec,
> > > or exec-only, etc.) without having to modify memslots.
> > > 
> > > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> > > userspace to operate on the per-page memory attributes.
> > >    - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
> > >      a guest memory range.
> > >    - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
> > >      memory attributes.
> > > 
> > > KVM internally uses xarray to store the per-page memory attributes.
> > > 
> > > Suggested-by: Sean Christopherson <seanjc@google.com>
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com/
> > > ---
> > >   Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++
> > >   arch/x86/kvm/Kconfig           |  1 +
> > >   include/linux/kvm_host.h       |  3 ++
> > >   include/uapi/linux/kvm.h       | 17 ++++++++
> > 
> > Should the changes introduced in this file also need to be added in
> > tools/include/uapi/linux/kvm.h ?
> 
> Yes I think.

I'm not sure how Paolo or others feel, but my preference is to never update KVM's
uapi headers in tools/ in KVM's tree.  Nothing KVM-related in tools/ actually
relies on the headers being copied into tools/, e.g. KVM selftests pulls KVM's
headers from the .../usr/include/ directory that's populated by `make headers_install`.

Perf's tooling is what actually "needs" the headers to be copied into tools/, so
my preference is to let the tools/perf maintainers deal with the headache of keeping
everything up-to-date.

> But I'm hesitate to include in this patch or not. I see many commits sync
> kernel kvm.h to tools's copy. Looks that is done periodically and with a
> 'pull' model.

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Sean Christopherson]

On Tue, Jan 17, 2023, Chao Peng wrote:
> On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> > >  
> > >  		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
> > >  			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> > > +
> > > +		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> > > +			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> > 
> > Synthesizing triple fault shutdown is not the right approach.  Even with TDX's
> > MCE "architecture" (heavy sarcasm), it's possible that host userspace and the
> > guest have a paravirt interface for handling memory errors without killing the
> > host.
> 
> Agree shutdown is not the correct choice. I see you made below change:
> 
> send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva, PAGE_SHIFT, current)
> 
> The MCE may happen in any thread than KVM thread, sending siginal to
> 'current' thread may not be the expected behavior.

This is already true today, e.g. a #MC in memory that is mapped into the guest can
be triggered by a host access.  Hrm, but in this case we actually have a KVM
instance, and we know that the #MC is relevant to the KVM instance, so I agree
that signaling 'current' is kludgy.

>  Also how userspace can tell is the MCE on the shared page or private page?
>  Do we care?

We care.  I was originally thinking we could require userspace to keep track of
things, but that's quite prescriptive and flawed, e.g. could race with conversions.

One option would be to KVM_EXIT_MEMORY_FAULT, and then wire up a generic (not x86
specific) KVM request to exit to userspace, e.g.

		/* KVM_EXIT_MEMORY_FAULT */
		struct {
#define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1ULL << 3)
#define KVM_MEMORY_EXIT_FLAG_HW_ERROR	(1ULL << 4)
			__u64 flags;
			__u64 gpa;
			__u64 size;
		} memory;

But I'm not sure that's the correct approach.  It kinda feels like we're reinventing
the wheel.  It seems like restrictedmem_get_page() _must_ be able to reject attempts
to get a poisoned page, i.e. restrictedmem_get_page() should yield KVM_PFN_ERR_HWPOISON.
Assuming that's the case, then I believe KVM simply needs to zap SPTEs in response
to an error notification in order to force vCPUs to fault on the poisoned page.

> > > +		return -EINVAL;
> > >  	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> > >  		return -EINVAL;
> > >  	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> > > @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > >  		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
> > >  			return -EINVAL;
> > >  	} else { /* Modify an existing slot. */
> > > +		/* Private memslots are immutable, they can only be deleted. */
> > 
> > I'm 99% certain I suggested this, but if we're going to make these memslots
> > immutable, then we should straight up disallow dirty logging, otherwise we'll
> > end up with a bizarre uAPI.
> 
> But in my mind dirty logging will be needed in the very short time, when
> live migration gets supported?

Ya, but if/when live migration support is added, private memslots will no longer
be immutable as userspace will want to enable dirty logging only when a VM is
being migrated, i.e. something will need to change.

Given that it looks like we have clear line of sight to SEV+UPM guests, my
preference would be to allow toggling dirty logging from the get-go.  It doesn't
necessarily have to be in the first patch, e.g. KVM could initially reject
KVM_MEM_LOG_DIRTY_PAGES + KVM_MEM_PRIVATE and then add support separately to make
the series easier to review, test, and bisect.

static int check_memory_region_flags(struct kvm *kvm,
				     const struct kvm_userspace_memory_region2 *mem)
{
	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;

	if (kvm_arch_has_private_mem(kvm) &&
	    ~(mem->flags & KVM_MEM_LOG_DIRTY_PAGES))
		valid_flags |= KVM_MEM_PRIVATE;


	...
}

> > > +		if (mem->flags & KVM_MEM_PRIVATE)
> > > +			return -EINVAL;
> > >  		if ((mem->userspace_addr != old->userspace_addr) ||
> > >  		    (npages != old->npages) ||
> > >  		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> > > @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > >  	new->npages = npages;
> > >  	new->flags = mem->flags;
> > >  	new->userspace_addr = mem->userspace_addr;
> > > +	if (mem->flags & KVM_MEM_PRIVATE) {
> > > +		new->restricted_file = fget(mem->restricted_fd);
> > > +		if (!new->restricted_file ||
> > > +		    !file_is_restrictedmem(new->restricted_file)) {
> > > +			r = -EINVAL;
> > > +			goto out;
> > > +		}
> > > +		new->restricted_offset = mem->restricted_offset;
> 
> I see you changed slot->restricted_offset type from loff_t to gfn_t and
> used pgoff_t when doing the restrictedmem_bind/unbind(). Using page
> index is reasonable KVM internally and sounds simpler than loff_t. But
> we also need initialize it to page index here as well as changes in
> another two cases. This is needed when restricted_offset != 0.

Oof.  I'm pretty sure I completely missed that loff_t is used for byte offsets,
whereas pgoff_t is a frame index. 

Given that the restrictmem APIs take pgoff_t, I definitely think it makes sense
to the index, but I'm very tempted to store pgoff_t instead of gfn_t, and name
the field "index" to help connect the dots to the rest of kernel, where "pgoff_t index"
is quite common.

And looking at those bits again, we should wrap all of the restrictedmem fields
with CONFIG_KVM_PRIVATE_MEM.  It'll require minor tweaks to __kvm_set_memory_region(),
but I think will yield cleaner code (and internal APIs) overall.

And wrap the three fields in an anonymous struct?  E.g. this is a little more
versbose (restrictedmem instead restricted), but at first glance it doesn't seem
to cause widespared line length issues.

#ifdef CONFIG_KVM_PRIVATE_MEM
	struct {
		struct file *file;
		pgoff_t index;
		struct restrictedmem_notifier notifier;
	} restrictedmem;
#endif

> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 547b92215002..49e375e78f30 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2364,8 +2364,7 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
>                                              gfn_t gfn, kvm_pfn_t *pfn,
>                                              int *order)
>  {
> -       pgoff_t index = gfn - slot->base_gfn +
> -                       (slot->restricted_offset >> PAGE_SHIFT);
> +       pgoff_t index = gfn - slot->base_gfn + slot->restricted_offset;
>         struct page *page;
>         int ret;
>  
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 01db35ddd5b3..7439bdcb0d04 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -935,7 +935,7 @@ static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
>                                          pgoff_t start, pgoff_t end,
>                                          gfn_t *gfn_start, gfn_t *gfn_end)
>  {
> -       unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> +       unsigned long base_pgoff = slot->restricted_offset;
>  
>         if (start > base_pgoff)
>                 *gfn_start = slot->base_gfn + start - base_pgoff;
> @@ -2275,7 +2275,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>                         r = -EINVAL;
>                         goto out;
>                 }
> -               new->restricted_offset = mem->restricted_offset;
> +               new->restricted_offset = mem->restricted_offset >> PAGE_SHIFT;
>         }
>  
>         r = kvm_set_memslot(kvm, old, new, change);
> 
> Chao
> > > +	}
> > > +
> > > +	new->kvm = kvm;
> > 
> > Set this above, just so that the code flows better.

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

On Tue, Jan 17, 2023 at 04:34:15PM +0000, Sean Christopherson wrote:
> On Tue, Jan 17, 2023, Chao Peng wrote:
> > On Fri, Jan 13, 2023 at 09:54:41PM +0000, Sean Christopherson wrote:
> > > > +	list_for_each_entry(notifier, &data->notifiers, list) {
> > > > +		notifier->ops->invalidate_start(notifier, start, end);
> > > 
> > > Two major design issues that we overlooked long ago:
> > > 
> > >   1. Blindly invoking notifiers will not scale.  E.g. if userspace configures a
> > >      VM with a large number of convertible memslots that are all backed by a
> > >      single large restrictedmem instance, then converting a single page will
> > >      result in a linear walk through all memslots.  I don't expect anyone to
> > >      actually do something silly like that, but I also never expected there to be
> > >      a legitimate usecase for thousands of memslots.
> > > 
> > >   2. This approach fails to provide the ability for KVM to ensure a guest has
> > >      exclusive access to a page.  As discussed in the past, the kernel can rely
> > >      on hardware (and maybe ARM's pKVM implementation?) for those guarantees, but
> > >      only for SNP and TDX VMs.  For VMs where userspace is trusted to some extent,
> > >      e.g. SEV, there is value in ensuring a 1:1 association.
> > > 
> > >      And probably more importantly, relying on hardware for SNP and TDX yields a
> > >      poor ABI and complicates KVM's internals.  If the kernel doesn't guarantee a
> > >      page is exclusive to a guest, i.e. if userspace can hand out the same page
> > >      from a restrictedmem instance to multiple VMs, then failure will occur only
> > >      when KVM tries to assign the page to the second VM.  That will happen deep
> > >      in KVM, which means KVM needs to gracefully handle such errors, and it means
> > >      that KVM's ABI effectively allows plumbing garbage into its memslots.
> > 
> > It may not be a valid usage, but in my TDX environment I do meet below
> > issue.
> > 
> > kvm_set_user_memory AddrSpace#0 Slot#0 flags=0x4 gpa=0x0 size=0x80000000 ua=0x7fe1ebfff000 ret=0
> > kvm_set_user_memory AddrSpace#0 Slot#1 flags=0x4 gpa=0xffc00000 size=0x400000 ua=0x7fe271579000 ret=0
> > kvm_set_user_memory AddrSpace#0 Slot#2 flags=0x4 gpa=0xfeda0000 size=0x20000 ua=0x7fe1ec09f000 ret=-22
> > 
> > Slot#2('SMRAM') is actually an alias into system memory(Slot#0) in QEMU
> > and slot#2 fails due to below exclusive check.
> > 
> > Currently I changed QEMU code to mark these alias slots as shared
> > instead of private but I'm not 100% confident this is correct fix.
> 
> That's a QEMU bug of sorts.  SMM is mutually exclusive with TDX, QEMU shouldn't
> be configuring SMRAM (or any SMM memslots for that matter) for TDX guests.

Thanks for the confirmation. As long as we only bind one notifier for
each address, using xarray does make things simple.

Chao

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Tue, Jan 17, 2023 at 07:35:58PM +0000, Sean Christopherson wrote:
> On Tue, Jan 17, 2023, Chao Peng wrote:
> > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> > > >  
> > > >  		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
> > > >  			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> > > > +
> > > > +		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> > > > +			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> > > 
> > > Synthesizing triple fault shutdown is not the right approach.  Even with TDX's
> > > MCE "architecture" (heavy sarcasm), it's possible that host userspace and the
> > > guest have a paravirt interface for handling memory errors without killing the
> > > host.
> > 
> > Agree shutdown is not the correct choice. I see you made below change:
> > 
> > send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva, PAGE_SHIFT, current)
> > 
> > The MCE may happen in any thread than KVM thread, sending siginal to
> > 'current' thread may not be the expected behavior.
> 
> This is already true today, e.g. a #MC in memory that is mapped into the guest can
> be triggered by a host access.  Hrm, but in this case we actually have a KVM
> instance, and we know that the #MC is relevant to the KVM instance, so I agree
> that signaling 'current' is kludgy.
> 
> >  Also how userspace can tell is the MCE on the shared page or private page?
> >  Do we care?
> 
> We care.  I was originally thinking we could require userspace to keep track of
> things, but that's quite prescriptive and flawed, e.g. could race with conversions.
> 
> One option would be to KVM_EXIT_MEMORY_FAULT, and then wire up a generic (not x86
> specific) KVM request to exit to userspace, e.g.
> 
> 		/* KVM_EXIT_MEMORY_FAULT */
> 		struct {
> #define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1ULL << 3)
> #define KVM_MEMORY_EXIT_FLAG_HW_ERROR	(1ULL << 4)
> 			__u64 flags;
> 			__u64 gpa;
> 			__u64 size;
> 		} memory;
> 
> But I'm not sure that's the correct approach.  It kinda feels like we're reinventing
> the wheel.  It seems like restrictedmem_get_page() _must_ be able to reject attempts
> to get a poisoned page, i.e. restrictedmem_get_page() should yield KVM_PFN_ERR_HWPOISON.

Yes, I see there is -EHWPOISON handling for hva_to_pfn() for shared
memory. It makes sense doing similar for private page.

> Assuming that's the case, then I believe KVM simply needs to zap SPTEs in response
> to an error notification in order to force vCPUs to fault on the poisoned page.

Agree, this is waht we should do anyway.

> 
> > > > +		return -EINVAL;
> > > >  	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> > > >  		return -EINVAL;
> > > >  	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> > > > @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > > >  		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
> > > >  			return -EINVAL;
> > > >  	} else { /* Modify an existing slot. */
> > > > +		/* Private memslots are immutable, they can only be deleted. */
> > > 
> > > I'm 99% certain I suggested this, but if we're going to make these memslots
> > > immutable, then we should straight up disallow dirty logging, otherwise we'll
> > > end up with a bizarre uAPI.
> > 
> > But in my mind dirty logging will be needed in the very short time, when
> > live migration gets supported?
> 
> Ya, but if/when live migration support is added, private memslots will no longer
> be immutable as userspace will want to enable dirty logging only when a VM is
> being migrated, i.e. something will need to change.
> 
> Given that it looks like we have clear line of sight to SEV+UPM guests, my
> preference would be to allow toggling dirty logging from the get-go.  It doesn't
> necessarily have to be in the first patch, e.g. KVM could initially reject
> KVM_MEM_LOG_DIRTY_PAGES + KVM_MEM_PRIVATE and then add support separately to make
> the series easier to review, test, and bisect.
> 
> static int check_memory_region_flags(struct kvm *kvm,
> 				     const struct kvm_userspace_memory_region2 *mem)
> {
> 	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> 
> 	if (kvm_arch_has_private_mem(kvm) &&
> 	    ~(mem->flags & KVM_MEM_LOG_DIRTY_PAGES))
> 		valid_flags |= KVM_MEM_PRIVATE;

Adding this limitation is OK to me. It's not too hard to remove it when
live migration gets added.

> 
> 
> 	...
> }
> 
> > > > +		if (mem->flags & KVM_MEM_PRIVATE)
> > > > +			return -EINVAL;
> > > >  		if ((mem->userspace_addr != old->userspace_addr) ||
> > > >  		    (npages != old->npages) ||
> > > >  		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> > > > @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > > >  	new->npages = npages;
> > > >  	new->flags = mem->flags;
> > > >  	new->userspace_addr = mem->userspace_addr;
> > > > +	if (mem->flags & KVM_MEM_PRIVATE) {
> > > > +		new->restricted_file = fget(mem->restricted_fd);
> > > > +		if (!new->restricted_file ||
> > > > +		    !file_is_restrictedmem(new->restricted_file)) {
> > > > +			r = -EINVAL;
> > > > +			goto out;
> > > > +		}
> > > > +		new->restricted_offset = mem->restricted_offset;
> > 
> > I see you changed slot->restricted_offset type from loff_t to gfn_t and
> > used pgoff_t when doing the restrictedmem_bind/unbind(). Using page
> > index is reasonable KVM internally and sounds simpler than loff_t. But
> > we also need initialize it to page index here as well as changes in
> > another two cases. This is needed when restricted_offset != 0.
> 
> Oof.  I'm pretty sure I completely missed that loff_t is used for byte offsets,
> whereas pgoff_t is a frame index. 
> 
> Given that the restrictmem APIs take pgoff_t, I definitely think it makes sense
> to the index, but I'm very tempted to store pgoff_t instead of gfn_t, and name
> the field "index" to help connect the dots to the rest of kernel, where "pgoff_t index"
> is quite common.
> 
> And looking at those bits again, we should wrap all of the restrictedmem fields
> with CONFIG_KVM_PRIVATE_MEM.  It'll require minor tweaks to __kvm_set_memory_region(),
> but I think will yield cleaner code (and internal APIs) overall.
> 
> And wrap the three fields in an anonymous struct?  E.g. this is a little more
> versbose (restrictedmem instead restricted), but at first glance it doesn't seem
> to cause widespared line length issues.
> 
> #ifdef CONFIG_KVM_PRIVATE_MEM
> 	struct {
> 		struct file *file;
> 		pgoff_t index;
> 		struct restrictedmem_notifier notifier;
> 	} restrictedmem;
> #endif

Looks better.

Thanks,
Chao
> 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 547b92215002..49e375e78f30 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -2364,8 +2364,7 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> >                                              gfn_t gfn, kvm_pfn_t *pfn,
> >                                              int *order)
> >  {
> > -       pgoff_t index = gfn - slot->base_gfn +
> > -                       (slot->restricted_offset >> PAGE_SHIFT);
> > +       pgoff_t index = gfn - slot->base_gfn + slot->restricted_offset;
> >         struct page *page;
> >         int ret;
> >  
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 01db35ddd5b3..7439bdcb0d04 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -935,7 +935,7 @@ static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
> >                                          pgoff_t start, pgoff_t end,
> >                                          gfn_t *gfn_start, gfn_t *gfn_end)
> >  {
> > -       unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> > +       unsigned long base_pgoff = slot->restricted_offset;
> >  
> >         if (start > base_pgoff)
> >                 *gfn_start = slot->base_gfn + start - base_pgoff;
> > @@ -2275,7 +2275,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >                         r = -EINVAL;
> >                         goto out;
> >                 }
> > -               new->restricted_offset = mem->restricted_offset;
> > +               new->restricted_offset = mem->restricted_offset >> PAGE_SHIFT;
> >         }
> >  
> >         r = kvm_set_memslot(kvm, old, new, change);
> > 
> > Chao
> > > > +	}
> > > > +
> > > > +	new->kvm = kvm;
> > > 
> > > Set this above, just so that the code flows better.

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Isaku Yamahata]

On Wed, Jan 18, 2023 at 04:16:41PM +0800,
Chao Peng <chao.p.peng@linux.intel.com> wrote:

> On Tue, Jan 17, 2023 at 04:34:15PM +0000, Sean Christopherson wrote:
> > On Tue, Jan 17, 2023, Chao Peng wrote:
> > > On Fri, Jan 13, 2023 at 09:54:41PM +0000, Sean Christopherson wrote:
> > > > > +	list_for_each_entry(notifier, &data->notifiers, list) {
> > > > > +		notifier->ops->invalidate_start(notifier, start, end);
> > > > 
> > > > Two major design issues that we overlooked long ago:
> > > > 
> > > >   1. Blindly invoking notifiers will not scale.  E.g. if userspace configures a
> > > >      VM with a large number of convertible memslots that are all backed by a
> > > >      single large restrictedmem instance, then converting a single page will
> > > >      result in a linear walk through all memslots.  I don't expect anyone to
> > > >      actually do something silly like that, but I also never expected there to be
> > > >      a legitimate usecase for thousands of memslots.
> > > > 
> > > >   2. This approach fails to provide the ability for KVM to ensure a guest has
> > > >      exclusive access to a page.  As discussed in the past, the kernel can rely
> > > >      on hardware (and maybe ARM's pKVM implementation?) for those guarantees, but
> > > >      only for SNP and TDX VMs.  For VMs where userspace is trusted to some extent,
> > > >      e.g. SEV, there is value in ensuring a 1:1 association.
> > > > 
> > > >      And probably more importantly, relying on hardware for SNP and TDX yields a
> > > >      poor ABI and complicates KVM's internals.  If the kernel doesn't guarantee a
> > > >      page is exclusive to a guest, i.e. if userspace can hand out the same page
> > > >      from a restrictedmem instance to multiple VMs, then failure will occur only
> > > >      when KVM tries to assign the page to the second VM.  That will happen deep
> > > >      in KVM, which means KVM needs to gracefully handle such errors, and it means
> > > >      that KVM's ABI effectively allows plumbing garbage into its memslots.
> > > 
> > > It may not be a valid usage, but in my TDX environment I do meet below
> > > issue.
> > > 
> > > kvm_set_user_memory AddrSpace#0 Slot#0 flags=0x4 gpa=0x0 size=0x80000000 ua=0x7fe1ebfff000 ret=0
> > > kvm_set_user_memory AddrSpace#0 Slot#1 flags=0x4 gpa=0xffc00000 size=0x400000 ua=0x7fe271579000 ret=0
> > > kvm_set_user_memory AddrSpace#0 Slot#2 flags=0x4 gpa=0xfeda0000 size=0x20000 ua=0x7fe1ec09f000 ret=-22
> > > 
> > > Slot#2('SMRAM') is actually an alias into system memory(Slot#0) in QEMU
> > > and slot#2 fails due to below exclusive check.
> > > 
> > > Currently I changed QEMU code to mark these alias slots as shared
> > > instead of private but I'm not 100% confident this is correct fix.
> > 
> > That's a QEMU bug of sorts.  SMM is mutually exclusive with TDX, QEMU shouldn't
> > be configuring SMRAM (or any SMM memslots for that matter) for TDX guests.
> 
> Thanks for the confirmation. As long as we only bind one notifier for
> each address, using xarray does make things simple.

In the past, I had patches for qemu to disable PAM and SMRAM, but they were
dropped for simplicity because SMRAM/PAM are disabled as reset state with unused
memslot registered. TDX guest bios(TDVF or EDK2) doesn't enable them.
Now we can revive them.
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Isaku Yamahata]

On Sat, Jan 14, 2023 at 12:37:59AM +0000,
Sean Christopherson <seanjc@google.com> wrote:

> On Fri, Dec 02, 2022, Chao Peng wrote:
> > This patch series implements KVM guest private memory for confidential
> > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > TDX-protected guest memory, machine check can happen which can further
> > crash the running host system, this is terrible for multi-tenant
> > configurations. The host accesses include those from KVM userspace like
> > QEMU. This series addresses KVM userspace induced crash by introducing
> > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > via a fd-based approach, but it can never access the guest memory
> > content.
> > 
> > The patch series touches both core mm and KVM code. I appreciate
> > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > reviews are always welcome.
> >   - 01: mm change, target for mm tree
> >   - 02-09: KVM change, target for KVM tree
> 
> A version with all of my feedback, plus reworked versions of Vishal's selftest,
> is available here:
> 
>   git@github.com:sean-jc/linux.git x86/upm_base_support
> 
> It compiles and passes the selftest, but it's otherwise barely tested.  There are
> a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> a WIP.
> 
> As for next steps, can you (handwaving all of the TDX folks) take a look at what
> I pushed and see if there's anything horrifically broken, and that it still works
> for TDX?
> 
> Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> (and I mean that).
> 
> On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> merging so that the criteria for merging are clear, and so that if the list is large
> (haven't thought much yet), the work of writing and running tests can be distributed.
> 
> Regarding downstream dependencies, before this lands, I want to pull in all the
> TDX and SNP series and see how everything fits together.  Specifically, I want to
> make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> don't miss an opportunity to make things simpler.  The patches in the SNP series to
> add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> details.  Nothing remotely major, but something that needs attention since it'll
> be uAPI.

Although I'm still debuging with TDX KVM, I needed the following.
kvm_faultin_pfn() is called without mmu_lock held.  the race to change
private/shared is handled by mmu_seq.  Maybe dedicated function only for
kvm_faultin_pfn().

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 02be5e1cba1e..38699ca75ab8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2322,7 +2322,7 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
 static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)
 {
-       lockdep_assert_held(&kvm->mmu_lock);
+       // lockdep_assert_held(&kvm->mmu_lock);
 
        return xa_to_value(xa_load(&kvm->mem_attr_array, gfn));
 }


-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> On Sat, Jan 14, 2023 at 12:37:59AM +0000,
> Sean Christopherson <seanjc@google.com> wrote:
> 
> > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > This patch series implements KVM guest private memory for confidential
> > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > TDX-protected guest memory, machine check can happen which can further
> > > crash the running host system, this is terrible for multi-tenant
> > > configurations. The host accesses include those from KVM userspace like
> > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > via a fd-based approach, but it can never access the guest memory
> > > content.
> > > 
> > > The patch series touches both core mm and KVM code. I appreciate
> > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > reviews are always welcome.
> > >   - 01: mm change, target for mm tree
> > >   - 02-09: KVM change, target for KVM tree
> > 
> > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > is available here:
> > 
> >   git@github.com:sean-jc/linux.git x86/upm_base_support
> > 
> > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > a WIP.
> > 
> > As for next steps, can you (handwaving all of the TDX folks) take a look at what
> > I pushed and see if there's anything horrifically broken, and that it still works
> > for TDX?
> > 
> > Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> > (and I mean that).
> > 
> > On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> > (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> > merging so that the criteria for merging are clear, and so that if the list is large
> > (haven't thought much yet), the work of writing and running tests can be distributed.
> > 
> > Regarding downstream dependencies, before this lands, I want to pull in all the
> > TDX and SNP series and see how everything fits together.  Specifically, I want to
> > make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> > don't miss an opportunity to make things simpler.  The patches in the SNP series to
> > add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> > details.  Nothing remotely major, but something that needs attention since it'll
> > be uAPI.
> 
> Although I'm still debuging with TDX KVM, I needed the following.
> kvm_faultin_pfn() is called without mmu_lock held.  the race to change
> private/shared is handled by mmu_seq.  Maybe dedicated function only for
> kvm_faultin_pfn().

Gah, you're not on the other thread where this was discussed[*].  Simply deleting
the lockdep assertion is safe, for guest types that rely on the attributes to
define shared vs. private, KVM rechecks the attributes under the protection of
mmu_seq.

I'll get a fixed version pushed out today.

[*] https://lore.kernel.org/all/Y8gpl+LwSuSgBFks@google.com

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Isaku Yamahata]

On Thu, Jan 19, 2023 at 03:25:08PM +0000,
Sean Christopherson <seanjc@google.com> wrote:

> On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > On Sat, Jan 14, 2023 at 12:37:59AM +0000,
> > Sean Christopherson <seanjc@google.com> wrote:
> > 
> > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > This patch series implements KVM guest private memory for confidential
> > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > TDX-protected guest memory, machine check can happen which can further
> > > > crash the running host system, this is terrible for multi-tenant
> > > > configurations. The host accesses include those from KVM userspace like
> > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > via a fd-based approach, but it can never access the guest memory
> > > > content.
> > > > 
> > > > The patch series touches both core mm and KVM code. I appreciate
> > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > reviews are always welcome.
> > > >   - 01: mm change, target for mm tree
> > > >   - 02-09: KVM change, target for KVM tree
> > > 
> > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > is available here:
> > > 
> > >   git@github.com:sean-jc/linux.git x86/upm_base_support
> > > 
> > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > a WIP.
> > > 
> > > As for next steps, can you (handwaving all of the TDX folks) take a look at what
> > > I pushed and see if there's anything horrifically broken, and that it still works
> > > for TDX?
> > > 
> > > Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> > > (and I mean that).
> > > 
> > > On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> > > (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> > > merging so that the criteria for merging are clear, and so that if the list is large
> > > (haven't thought much yet), the work of writing and running tests can be distributed.
> > > 
> > > Regarding downstream dependencies, before this lands, I want to pull in all the
> > > TDX and SNP series and see how everything fits together.  Specifically, I want to
> > > make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> > > don't miss an opportunity to make things simpler.  The patches in the SNP series to
> > > add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> > > details.  Nothing remotely major, but something that needs attention since it'll
> > > be uAPI.
> > 
> > Although I'm still debuging with TDX KVM, I needed the following.
> > kvm_faultin_pfn() is called without mmu_lock held.  the race to change
> > private/shared is handled by mmu_seq.  Maybe dedicated function only for
> > kvm_faultin_pfn().
> 
> Gah, you're not on the other thread where this was discussed[*].  Simply deleting
> the lockdep assertion is safe, for guest types that rely on the attributes to
> define shared vs. private, KVM rechecks the attributes under the protection of
> mmu_seq.
> 
> I'll get a fixed version pushed out today.
> 
> [*] https://lore.kernel.org/all/Y8gpl+LwSuSgBFks@google.com

Now I have tdx kvm working. I've uploaded at the followings.
It's rebased to v6.2-rc3.
        git@github.com:yamahata/linux.git tdx/upm
        git@github.com:yamahata/qemu.git tdx/upm

kvm_mmu_do_page_fault() needs the following change.
kvm_mem_is_private() queries mem_attr_array.  kvm_faultin_pfn() also uses
kvm_mem_is_private(). So the shared-private check in kvm_faultin_pfn() doesn't
make sense. This change would belong to TDX KVM patches, though.

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 72b0da8e27e0..f45ac438bbf4 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -430,7 +430,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
                .max_level = vcpu->kvm->arch.tdp_max_page_level,
                .req_level = PG_LEVEL_4K,
                .goal_level = PG_LEVEL_4K,
-               .is_private = kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
+               .is_private = kvm_is_private_gpa(vcpu->kvm, cr2_or_gpa),
        };
        int r;


-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Jarkko Sakkinen]

On Mon, Jan 09, 2023 at 07:32:05PM +0000, Sean Christopherson wrote:
> On Fri, Jan 06, 2023, Chao Peng wrote:
> > On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote:
> > > On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > > > To make future maintenance easy, internally use a binary compatible
> > > > alias struct kvm_user_mem_region to handle both the normal and the
> > > > '_ext' variants.
> > > 
> > > Feels bit hacky IMHO, and more like a completely new feature than
> > > an extension.
> > > 
> > > Why not just add a new ioctl? The commit message does not address
> > > the most essential design here.
> > 
> > Yes, people can always choose to add a new ioctl for this kind of change
> > and the balance point here is we want to also avoid 'too many ioctls' if
> > the functionalities are similar.  The '_ext' variant reuses all the
> > existing fields in the 'normal' variant and most importantly KVM
> > internally can reuse most of the code. I certainly can add some words in
> > the commit message to explain this design choice.
> 
> After seeing the userspace side of this, I agree with Jarkko; overloading
> KVM_SET_USER_MEMORY_REGION is a hack.  E.g. the size validation ends up being
> bogus, and userspace ends up abusing unions or implementing kvm_user_mem_region
> itself.
> 
> It feels absolutely ridiculous, but I think the best option is to do:
> 
> #define KVM_SET_USER_MEMORY_REGION2 _IOW(KVMIO, 0x49, \
> 					 struct kvm_userspace_memory_region2)
> 
> /* for KVM_SET_USER_MEMORY_REGION2 */
> struct kvm_user_mem_region2 {
> 	__u32 slot;
> 	__u32 flags;
> 	__u64 guest_phys_addr;
> 	__u64 memory_size;
> 	__u64 userspace_addr;
> 	__u64 restricted_offset;
> 	__u32 restricted_fd;
> 	__u32 pad1;
> 	__u64 pad2[14];
> }
> 
> And it's consistent with other KVM ioctls(), e.g. KVM_SET_CPUID2.
> 
> Regarding the userspace side of things, please include Vishal's selftests in v11,
> it's impossible to properly review the uAPI changes without seeing the userspace
> side of things.  I'm in the process of reviewing Vishal's v2[*], I'll try to
> massage it into a set of patches that you can incorporate into your series.
> 
> [*] https://lore.kernel.org/all/20221205232341.4131240-1-vannapurve@google.com

+1

BR, Jarkko

Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

[Jarkko Sakkinen]

On Tue, Jan 10, 2023 at 05:14:32PM +0800, Chao Peng wrote:
> On Mon, Jan 09, 2023 at 07:32:05PM +0000, Sean Christopherson wrote:
> > On Fri, Jan 06, 2023, Chao Peng wrote:
> > > On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote:
> > > > On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> > > > > To make future maintenance easy, internally use a binary compatible
> > > > > alias struct kvm_user_mem_region to handle both the normal and the
> > > > > '_ext' variants.
> > > > 
> > > > Feels bit hacky IMHO, and more like a completely new feature than
> > > > an extension.
> > > > 
> > > > Why not just add a new ioctl? The commit message does not address
> > > > the most essential design here.
> > > 
> > > Yes, people can always choose to add a new ioctl for this kind of change
> > > and the balance point here is we want to also avoid 'too many ioctls' if
> > > the functionalities are similar.  The '_ext' variant reuses all the
> > > existing fields in the 'normal' variant and most importantly KVM
> > > internally can reuse most of the code. I certainly can add some words in
> > > the commit message to explain this design choice.
> > 
> > After seeing the userspace side of this, I agree with Jarkko; overloading
> > KVM_SET_USER_MEMORY_REGION is a hack.  E.g. the size validation ends up being
> > bogus, and userspace ends up abusing unions or implementing kvm_user_mem_region
> > itself.
> 
> How is the size validation being bogus? I don't quite follow. Then we
> will use kvm_userspace_memory_region2 as the KVM internal alias, right?
> I see similar examples use different functions to handle different
> versions but it does look easier if we use alias for this function.
> 
> > 
> > It feels absolutely ridiculous, but I think the best option is to do:
> > 
> > #define KVM_SET_USER_MEMORY_REGION2 _IOW(KVMIO, 0x49, \
> > 					 struct kvm_userspace_memory_region2)
> 
> Just interesting, is 0x49 a safe number we can use? 
> 
> > 
> > /* for KVM_SET_USER_MEMORY_REGION2 */
> > struct kvm_user_mem_region2 {
> > 	__u32 slot;
> > 	__u32 flags;
> > 	__u64 guest_phys_addr;
> > 	__u64 memory_size;
> > 	__u64 userspace_addr;
> > 	__u64 restricted_offset;
> > 	__u32 restricted_fd;
> > 	__u32 pad1;
> > 	__u64 pad2[14];
> > }
> > 
> > And it's consistent with other KVM ioctls(), e.g. KVM_SET_CPUID2.
> 
> Okay, agree from KVM userspace API perspective this is more consistent
> with similar existing examples. I see several of them.
> 
> I think we will also need a CAP_KVM_SET_USER_MEMORY_REGION2 for this new
> ioctl.

The current API in the patch set is trivial for C user space but for
any other more "constrained" language such as Rust a new ioctl would be
easier to adapt.

> > 
> > Regarding the userspace side of things, please include Vishal's selftests in v11,
> > it's impossible to properly review the uAPI changes without seeing the userspace
> > side of things.  I'm in the process of reviewing Vishal's v2[*], I'll try to
> > massage it into a set of patches that you can incorporate into your series.
> 
> Previously I included Vishal's selftests in the github repo, but not
> include them in this patch series. It's OK for me to incorporate them
> directly into this series and review together if Vishal is fine.
> 
> Chao
> > 
> > [*] https://lore.kernel.org/all/20221205232341.4131240-1-vannapurve@google.com

BR, Jarkko

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Vlastimil Babka]

On 12/22/22 01:37, Huang, Kai wrote:
>>> I argue that this page pinning (or page migration prevention) is not
>>> tied to where the page comes from, instead related to how the page will
>>> be used. Whether the page is restrictedmem backed or GUP() backed, once
>>> it's used by current version of TDX then the page pinning is needed. So
>>> such page migration prevention is really TDX thing, even not KVM generic
>>> thing (that's why I think we don't need change the existing logic of
>>> kvm_release_pfn_clean()). 
>>>
> This essentially boils down to who "owns" page migration handling, and sadly,
> page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
> migration by itself -- it's just a passive receiver.
> 
> For normal pages, page migration is totally done by the core-kernel (i.e. it
> unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
>> migrate_page() to actually migrate the page).
> In the sense of TDX, conceptually it should be done in the same way. The more
> important thing is: yes KVM can use get_page() to prevent page migration, but
> when KVM wants to support it, KVM cannot just remove get_page(), as the core-
> kernel will still just do migrate_page() which won't work for TDX (given
> restricted_memfd doesn't have a_ops->migrate_page() implemented).
> 
> So I think the restricted_memfd filesystem should own page migration handling,
> (i.e. by implementing a_ops->migrate_page() to either just reject page migration
> or somehow support it).

While this thread seems to be settled on refcounts already, just wanted
to point out that it wouldn't be ideal to prevent migrations by
a_ops->migrate_page() rejecting them. It would mean cputime wasted (i.e.
by memory compaction) by isolating the pages for migration and then
releasing them after the callback rejects it (at least we wouldn't waste
time creating and undoing migration entries in the userspace page tables
as there's no mmap). Elevated refcount on the other hand is detected
very early in compaction so no isolation is attempted, so from that
aspect it's optimal.

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Kirill A. Shutemov]

On Mon, Jan 23, 2023 at 03:03:45PM +0100, Vlastimil Babka wrote:
> On 12/22/22 01:37, Huang, Kai wrote:
> >>> I argue that this page pinning (or page migration prevention) is not
> >>> tied to where the page comes from, instead related to how the page will
> >>> be used. Whether the page is restrictedmem backed or GUP() backed, once
> >>> it's used by current version of TDX then the page pinning is needed. So
> >>> such page migration prevention is really TDX thing, even not KVM generic
> >>> thing (that's why I think we don't need change the existing logic of
> >>> kvm_release_pfn_clean()). 
> >>>
> > This essentially boils down to who "owns" page migration handling, and sadly,
> > page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
> > migration by itself -- it's just a passive receiver.
> > 
> > For normal pages, page migration is totally done by the core-kernel (i.e. it
> > unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
> >> migrate_page() to actually migrate the page).
> > In the sense of TDX, conceptually it should be done in the same way. The more
> > important thing is: yes KVM can use get_page() to prevent page migration, but
> > when KVM wants to support it, KVM cannot just remove get_page(), as the core-
> > kernel will still just do migrate_page() which won't work for TDX (given
> > restricted_memfd doesn't have a_ops->migrate_page() implemented).
> > 
> > So I think the restricted_memfd filesystem should own page migration handling,
> > (i.e. by implementing a_ops->migrate_page() to either just reject page migration
> > or somehow support it).
> 
> While this thread seems to be settled on refcounts already, just wanted
> to point out that it wouldn't be ideal to prevent migrations by
> a_ops->migrate_page() rejecting them. It would mean cputime wasted (i.e.
> by memory compaction) by isolating the pages for migration and then
> releasing them after the callback rejects it (at least we wouldn't waste
> time creating and undoing migration entries in the userspace page tables
> as there's no mmap). Elevated refcount on the other hand is detected
> very early in compaction so no isolation is attempted, so from that
> aspect it's optimal.

Hm. Do we need a new hook in a_ops to check if the page is migratable
before going with longer path to migrate_page().

Or maybe add AS_UNMOVABLE?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Kirill A. Shutemov]

On Thu, Dec 22, 2022 at 06:15:24PM +0000, Sean Christopherson wrote:
> On Wed, Dec 21, 2022, Chao Peng wrote:
> > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > > refcount after setting up mapping in the secondary mmu, otherwise the page will
> > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> > 
> > That's true. Actually even true for restrictedmem case, most likely we
> > will still need the kvm_release_pfn_clean() for KVM generic code. On one
> > side, other restrictedmem users like pKVM may not require page pinning
> > at all. On the other side, see below.
> > 
> > > 
> > > So what we are expecting is: for KVM if the page comes from restricted mem, then
> > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.
> 
> No, requiring the user (KVM) to guard against lack of support for page migration
> in restricted mem is a terrible API.  It's totally fine for restricted mem to not
> support page migration until there's a use case, but punting the problem to KVM
> is not acceptable.  Restricted mem itself doesn't yet support page migration,
> e.g. explosions would occur even if KVM wanted to allow migration since there is
> no notification to invalidate existing mappings.

I tried to find a way to hook into migration path from restrictedmem. It
is not easy because from code-mm PoV the restrictedmem page just yet
another shmem page.

It is somewhat dubious, but I think it should be safe to override
mapping->a_ops for the shmem mapping.

It also eliminates need in special treatment for the restrictedmem pages
from memory-failure code.

shmem_mapping() uses ->a_ops to detect shmem mapping. Modify the
implementation to still be true for restrictedmem pages.

Build tested only.

Any comments?

diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
index 6fddb08f03cc..73ded3c3bad1 100644
--- a/include/linux/restrictedmem.h
+++ b/include/linux/restrictedmem.h
@@ -36,8 +36,6 @@ static inline bool file_is_restrictedmem(struct file *file)
 	return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC;
 }
 
-void restrictedmem_error_page(struct page *page, struct address_space *mapping);
-
 #else
 
 static inline bool file_is_restrictedmem(struct file *file)
@@ -45,11 +43,6 @@ static inline bool file_is_restrictedmem(struct file *file)
 	return false;
 }
 
-static inline void restrictedmem_error_page(struct page *page,
-					    struct address_space *mapping)
-{
-}
-
 #endif /* CONFIG_RESTRICTEDMEM */
 
 #endif /* _LINUX_RESTRICTEDMEM_H */
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index d500ea967dc7..a4af160f37e4 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -9,6 +9,7 @@
 #include <linux/percpu_counter.h>
 #include <linux/xattr.h>
 #include <linux/fs_parser.h>
+#include <linux/magic.h>
 
 /* inode in-kernel data */
 
@@ -75,10 +76,9 @@ extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
 		unsigned long len, unsigned long pgoff, unsigned long flags);
 extern int shmem_lock(struct file *file, int lock, struct ucounts *ucounts);
 #ifdef CONFIG_SHMEM
-extern const struct address_space_operations shmem_aops;
 static inline bool shmem_mapping(struct address_space *mapping)
 {
-	return mapping->a_ops == &shmem_aops;
+	return mapping->host->i_sb->s_magic == TMPFS_MAGIC;
 }
 #else
 static inline bool shmem_mapping(struct address_space *mapping)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index f91b444e471e..145bb561ddb3 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -62,7 +62,6 @@
 #include <linux/page-isolation.h>
 #include <linux/pagewalk.h>
 #include <linux/shmem_fs.h>
-#include <linux/restrictedmem.h>
 #include "swap.h"
 #include "internal.h"
 #include "ras/ras_event.h"
@@ -941,8 +940,6 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
 		goto out;
 	}
 
-	restrictedmem_error_page(p, mapping);
-
 	/*
 	 * The shmem page is kept in page cache instead of truncating
 	 * so is expected to have an extra refcount after error-handling.
diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
index 15c52301eeb9..d0ca609b82cb 100644
--- a/mm/restrictedmem.c
+++ b/mm/restrictedmem.c
@@ -189,6 +189,51 @@ static struct file *restrictedmem_file_create(struct file *memfd)
 	return file;
 }
 
+static int restricted_error_remove_page(struct address_space *mapping,
+					struct page *page)
+{
+	struct super_block *sb = restrictedmem_mnt->mnt_sb;
+	struct inode *inode, *next;
+	pgoff_t start, end;
+
+	start = page->index;
+	end = start + thp_nr_pages(page);
+
+	spin_lock(&sb->s_inode_list_lock);
+	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
+		struct restrictedmem *rm = inode->i_mapping->private_data;
+		struct restrictedmem_notifier *notifier;
+		struct file *memfd = rm->memfd;
+		unsigned long index;
+
+		if (memfd->f_mapping != mapping)
+			continue;
+
+		xa_for_each_range(&rm->bindings, index, notifier, start, end)
+			notifier->ops->error(notifier, start, end);
+		break;
+	}
+	spin_unlock(&sb->s_inode_list_lock);
+
+	return 0;
+}
+
+#ifdef CONFIG_MIGRATION
+static int restricted_folio(struct address_space *mapping, struct folio *dst,
+			    struct folio *src, enum migrate_mode mode)
+{
+	return -EBUSY;
+}
+#endif
+
+static struct address_space_operations restricted_aops = {
+	.dirty_folio	= noop_dirty_folio,
+	.error_remove_page = restricted_error_remove_page,
+#ifdef CONFIG_MIGRATION
+	.migrate_folio	= restricted_folio,
+#endif
+};
+
 SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
 {
 	struct file *file, *restricted_file;
@@ -209,6 +254,8 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
 	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
 	file->f_flags |= O_LARGEFILE;
 
+	file->f_mapping->a_ops = &restricted_aops;
+
 	restricted_file = restrictedmem_file_create(file);
 	if (IS_ERR(restricted_file)) {
 		err = PTR_ERR(restricted_file);
@@ -293,31 +340,3 @@ int restrictedmem_get_page(struct file *file, pgoff_t offset,
 }
 EXPORT_SYMBOL_GPL(restrictedmem_get_page);
 
-void restrictedmem_error_page(struct page *page, struct address_space *mapping)
-{
-	struct super_block *sb = restrictedmem_mnt->mnt_sb;
-	struct inode *inode, *next;
-	pgoff_t start, end;
-
-	if (!shmem_mapping(mapping))
-		return;
-
-	start = page->index;
-	end = start + thp_nr_pages(page);
-
-	spin_lock(&sb->s_inode_list_lock);
-	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
-		struct restrictedmem *rm = inode->i_mapping->private_data;
-		struct restrictedmem_notifier *notifier;
-		struct file *memfd = rm->memfd;
-		unsigned long index;
-
-		if (memfd->f_mapping != mapping)
-			continue;
-
-		xa_for_each_range(&rm->bindings, index, notifier, start, end)
-			notifier->ops->error(notifier, start, end);
-		break;
-	}
-	spin_unlock(&sb->s_inode_list_lock);
-}
diff --git a/mm/shmem.c b/mm/shmem.c
index c1d8b8a1aa3b..3df4d95784b9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -231,7 +231,7 @@ static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
 }
 
 static const struct super_operations shmem_ops;
-const struct address_space_operations shmem_aops;
+static const struct address_space_operations shmem_aops;
 static const struct file_operations shmem_file_operations;
 static const struct inode_operations shmem_inode_operations;
 static const struct inode_operations shmem_dir_inode_operations;
@@ -3894,7 +3894,7 @@ static int shmem_error_remove_page(struct address_space *mapping,
 	return 0;
 }
 
-const struct address_space_operations shmem_aops = {
+static const struct address_space_operations shmem_aops = {
 	.writepage	= shmem_writepage,
 	.dirty_folio	= noop_dirty_folio,
 #ifdef CONFIG_TMPFS
@@ -3906,7 +3906,6 @@ const struct address_space_operations shmem_aops = {
 #endif
 	.error_remove_page = shmem_error_remove_page,
 };
-EXPORT_SYMBOL(shmem_aops);
 
 static const struct file_operations shmem_file_operations = {
 	.mmap		= shmem_mmap,
-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Huang, Kai]

On Mon, 2023-01-23 at 15:03 +0100, Vlastimil Babka wrote:
> On 12/22/22 01:37, Huang, Kai wrote:
> > > > I argue that this page pinning (or page migration prevention) is not
> > > > tied to where the page comes from, instead related to how the page will
> > > > be used. Whether the page is restrictedmem backed or GUP() backed, once
> > > > it's used by current version of TDX then the page pinning is needed. So
> > > > such page migration prevention is really TDX thing, even not KVM generic
> > > > thing (that's why I think we don't need change the existing logic of
> > > > kvm_release_pfn_clean()). 
> > > > 
> > This essentially boils down to who "owns" page migration handling, and sadly,
> > page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
> > migration by itself -- it's just a passive receiver.
> > 
> > For normal pages, page migration is totally done by the core-kernel (i.e. it
> > unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
> > > migrate_page() to actually migrate the page).
> > In the sense of TDX, conceptually it should be done in the same way. The more
> > important thing is: yes KVM can use get_page() to prevent page migration, but
> > when KVM wants to support it, KVM cannot just remove get_page(), as the core-
> > kernel will still just do migrate_page() which won't work for TDX (given
> > restricted_memfd doesn't have a_ops->migrate_page() implemented).
> > 
> > So I think the restricted_memfd filesystem should own page migration handling,
> > (i.e. by implementing a_ops->migrate_page() to either just reject page migration
> > or somehow support it).
> 
> While this thread seems to be settled on refcounts already, 
> 

I am not sure but will let Sean/Paolo to decide.

> just wanted
> to point out that it wouldn't be ideal to prevent migrations by
> a_ops->migrate_page() rejecting them. It would mean cputime wasted (i.e.
> by memory compaction) by isolating the pages for migration and then
> releasing them after the callback rejects it (at least we wouldn't waste
> time creating and undoing migration entries in the userspace page tables
> as there's no mmap). Elevated refcount on the other hand is detected
> very early in compaction so no isolation is attempted, so from that
> aspect it's optimal.

I am probably missing something, but IIUC the checking of refcount happens at
very last stage of page migration too, for instance:

	migrate_folio(...) ->
		migrate_folio_extra(..., 0 /* extra_count */) ->
			folio_migrate_mapping(...).

And it is folio_migrate_mapping() who does the actual compare with the refcount,
which is at very late stage too:

int folio_migrate_mapping(struct address_space *mapping,
                struct folio *newfolio, struct folio *folio, int extra_count)
{
	...
        int expected_count = folio_expected_refs(mapping, folio) + extra_count;

        if (!mapping) {
                /* Anonymous page without mapping */
                if (folio_ref_count(folio) != expected_count)
                        return -EAGAIN;

		....
                return MIGRATEPAGE_SUCCESS;
        }

	....
        if (!folio_ref_freeze(folio, expected_count)) {
                xas_unlock_irq(&xas);
                return -EAGAIN;
        }
	...
}

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Sean Christopherson]

On Mon, Jan 23, 2023, Huang, Kai wrote:
> On Mon, 2023-01-23 at 15:03 +0100, Vlastimil Babka wrote:
> > On 12/22/22 01:37, Huang, Kai wrote:
> > > > > I argue that this page pinning (or page migration prevention) is not
> > > > > tied to where the page comes from, instead related to how the page will
> > > > > be used. Whether the page is restrictedmem backed or GUP() backed, once
> > > > > it's used by current version of TDX then the page pinning is needed. So
> > > > > such page migration prevention is really TDX thing, even not KVM generic
> > > > > thing (that's why I think we don't need change the existing logic of
> > > > > kvm_release_pfn_clean()). 
> > > > > 
> > > This essentially boils down to who "owns" page migration handling, and sadly,
> > > page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
> > > migration by itself -- it's just a passive receiver.
> > > 
> > > For normal pages, page migration is totally done by the core-kernel (i.e. it
> > > unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
> > > > migrate_page() to actually migrate the page).
> > > In the sense of TDX, conceptually it should be done in the same way. The more
> > > important thing is: yes KVM can use get_page() to prevent page migration, but
> > > when KVM wants to support it, KVM cannot just remove get_page(), as the core-
> > > kernel will still just do migrate_page() which won't work for TDX (given
> > > restricted_memfd doesn't have a_ops->migrate_page() implemented).
> > > 
> > > So I think the restricted_memfd filesystem should own page migration handling,
> > > (i.e. by implementing a_ops->migrate_page() to either just reject page migration
> > > or somehow support it).
> > 
> > While this thread seems to be settled on refcounts already, 
> > 
> 
> I am not sure but will let Sean/Paolo to decide.

My preference is whatever is most performant without being hideous :-)

> > just wanted
> > to point out that it wouldn't be ideal to prevent migrations by
> > a_ops->migrate_page() rejecting them. It would mean cputime wasted (i.e.
> > by memory compaction) by isolating the pages for migration and then
> > releasing them after the callback rejects it (at least we wouldn't waste
> > time creating and undoing migration entries in the userspace page tables
> > as there's no mmap). Elevated refcount on the other hand is detected
> > very early in compaction so no isolation is attempted, so from that
> > aspect it's optimal.
> 
> I am probably missing something,

Heh, me too, I could have sworn that using refcounts was the least efficient way
to block migration.

> but IIUC the checking of refcount happens at very last stage of page migration too 

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> On Thu, Jan 19, 2023 at 03:25:08PM +0000,
> Sean Christopherson <seanjc@google.com> wrote:
> 
> > On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > > On Sat, Jan 14, 2023 at 12:37:59AM +0000,
> > > Sean Christopherson <seanjc@google.com> wrote:
> > > 
> > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > This patch series implements KVM guest private memory for confidential
> > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > > TDX-protected guest memory, machine check can happen which can further
> > > > > crash the running host system, this is terrible for multi-tenant
> > > > > configurations. The host accesses include those from KVM userspace like
> > > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > > via a fd-based approach, but it can never access the guest memory
> > > > > content.
> > > > > 
> > > > > The patch series touches both core mm and KVM code. I appreciate
> > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > > reviews are always welcome.
> > > > >   - 01: mm change, target for mm tree
> > > > >   - 02-09: KVM change, target for KVM tree
> > > > 
> > > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > > is available here:
> > > > 
> > > >   git@github.com:sean-jc/linux.git x86/upm_base_support
> > > > 
> > > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > > a WIP.
> > > > 
> > > > As for next steps, can you (handwaving all of the TDX folks) take a look at what
> > > > I pushed and see if there's anything horrifically broken, and that it still works
> > > > for TDX?
> > > > 
> > > > Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> > > > (and I mean that).
> > > > 
> > > > On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> > > > (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> > > > merging so that the criteria for merging are clear, and so that if the list is large
> > > > (haven't thought much yet), the work of writing and running tests can be distributed.
> > > > 
> > > > Regarding downstream dependencies, before this lands, I want to pull in all the
> > > > TDX and SNP series and see how everything fits together.  Specifically, I want to
> > > > make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> > > > don't miss an opportunity to make things simpler.  The patches in the SNP series to
> > > > add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> > > > details.  Nothing remotely major, but something that needs attention since it'll
> > > > be uAPI.
> > > 
> > > Although I'm still debuging with TDX KVM, I needed the following.
> > > kvm_faultin_pfn() is called without mmu_lock held.  the race to change
> > > private/shared is handled by mmu_seq.  Maybe dedicated function only for
> > > kvm_faultin_pfn().
> > 
> > Gah, you're not on the other thread where this was discussed[*].  Simply deleting
> > the lockdep assertion is safe, for guest types that rely on the attributes to
> > define shared vs. private, KVM rechecks the attributes under the protection of
> > mmu_seq.
> > 
> > I'll get a fixed version pushed out today.
> > 
> > [*] https://lore.kernel.org/all/Y8gpl+LwSuSgBFks@google.com
> 
> Now I have tdx kvm working. I've uploaded at the followings.
> It's rebased to v6.2-rc3.
>         git@github.com:yamahata/linux.git tdx/upm
>         git@github.com:yamahata/qemu.git tdx/upm

And I finally got a working, building version updated and pushed out (again to):

  git@github.com:sean-jc/linux.git x86/upm_base_support

Took longer than expected to get the memslot restrictions sussed out.  I'm done
working on the code for now, my plan is to come back to it+TDX+SNP in 2-3 weeks
to resolves any remaining todos (that no one else tackles) and to do the whole
"merge the world" excersise.

> kvm_mmu_do_page_fault() needs the following change.
> kvm_mem_is_private() queries mem_attr_array.  kvm_faultin_pfn() also uses
> kvm_mem_is_private(). So the shared-private check in kvm_faultin_pfn() doesn't
> make sense. This change would belong to TDX KVM patches, though.

Yeah, SNP needs similar treatment.  Sorting that out is high up on the todo list.

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Vlastimil Babka]

On 1/24/23 00:38, Sean Christopherson wrote:
> On Mon, Jan 23, 2023, Huang, Kai wrote:
>> On Mon, 2023-01-23 at 15:03 +0100, Vlastimil Babka wrote:
>>> On 12/22/22 01:37, Huang, Kai wrote:
>>>>>> I argue that this page pinning (or page migration prevention) is not
>>>>>> tied to where the page comes from, instead related to how the page will
>>>>>> be used. Whether the page is restrictedmem backed or GUP() backed, once
>>>>>> it's used by current version of TDX then the page pinning is needed. So
>>>>>> such page migration prevention is really TDX thing, even not KVM generic
>>>>>> thing (that's why I think we don't need change the existing logic of
>>>>>> kvm_release_pfn_clean()). 
>>>>>>
>>>> This essentially boils down to who "owns" page migration handling, and sadly,
>>>> page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
>>>> migration by itself -- it's just a passive receiver.
>>>>
>>>> For normal pages, page migration is totally done by the core-kernel (i.e. it
>>>> unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
>>>>> migrate_page() to actually migrate the page).
>>>> In the sense of TDX, conceptually it should be done in the same way. The more
>>>> important thing is: yes KVM can use get_page() to prevent page migration, but
>>>> when KVM wants to support it, KVM cannot just remove get_page(), as the core-
>>>> kernel will still just do migrate_page() which won't work for TDX (given
>>>> restricted_memfd doesn't have a_ops->migrate_page() implemented).
>>>>
>>>> So I think the restricted_memfd filesystem should own page migration handling,
>>>> (i.e. by implementing a_ops->migrate_page() to either just reject page migration
>>>> or somehow support it).
>>>
>>> While this thread seems to be settled on refcounts already, 
>>>
>>
>> I am not sure but will let Sean/Paolo to decide.
> 
> My preference is whatever is most performant without being hideous :-)
> 
>>> just wanted
>>> to point out that it wouldn't be ideal to prevent migrations by
>>> a_ops->migrate_page() rejecting them. It would mean cputime wasted (i.e.
>>> by memory compaction) by isolating the pages for migration and then
>>> releasing them after the callback rejects it (at least we wouldn't waste
>>> time creating and undoing migration entries in the userspace page tables
>>> as there's no mmap). Elevated refcount on the other hand is detected
>>> very early in compaction so no isolation is attempted, so from that
>>> aspect it's optimal.
>>
>> I am probably missing something,
> 
> Heh, me too, I could have sworn that using refcounts was the least efficient way
> to block migration.

Well I admit that due to my experience with it, I do mostly consider
migration through memory compaction POV, which is a significant user of
migration on random pages that's not requested by userspace actions on
specific ranges.

And compaction has in isolate_migratepages_block():

/*
 * Migration will fail if an anonymous page is pinned in memory,
 * so avoid taking lru_lock and isolating it unnecessarily in an
 * admittedly racy check.
 */
mapping = page_mapping(page);
if (!mapping && page_count(page) > page_mapcount(page))
        goto isolate_fail;

so that prevents migration of pages with elevated refcount very early,
before they are even isolated, so before migrate_pages() is called.

But it's true there are other sources of "random pages migration" - numa
balancing, demotion in lieu of reclaim... and I'm not sure if all have
such early check too.

Anyway, whatever is decided to be a better way than elevated refcounts,
would ideally be checked before isolation as well, as that's the most
efficient way.

>> but IIUC the checking of refcount happens at very last stage of page migration too 

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Liam Merwick]

On 14/01/2023 00:37, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
>> This patch series implements KVM guest private memory for confidential
>> computing scenarios like Intel TDX[1]. If a TDX host accesses
>> TDX-protected guest memory, machine check can happen which can further
>> crash the running host system, this is terrible for multi-tenant
>> configurations. The host accesses include those from KVM userspace like
>> QEMU. This series addresses KVM userspace induced crash by introducing
>> new mm and KVM interfaces so KVM userspace can still manage guest memory
>> via a fd-based approach, but it can never access the guest memory
>> content.
>>
>> The patch series touches both core mm and KVM code. I appreciate
>> Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
>> reviews are always welcome.
>>    - 01: mm change, target for mm tree
>>    - 02-09: KVM change, target for KVM tree
> 
> A version with all of my feedback, plus reworked versions of Vishal's selftest,
> is available here:
> 
>    git@github.com:sean-jc/linux.git x86/upm_base_support
> 
> It compiles and passes the selftest, but it's otherwise barely tested.  There are
> a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> a WIP.
> 

When running LTP (https://github.com/linux-test-project/ltp) on the v10
bits (and also with Sean's branch above) I encounter the following NULL
pointer dereference with testcases/kernel/syscalls/madvise/madvise01
(100% reproducible).

It appears that in restrictedmem_error_page() 
inode->i_mapping->private_data is NULL
in the list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list)
but I don't know why.


[ 5365.177168] BUG: kernel NULL pointer dereference, address: 
0000000000000028
[ 5365.178881] #PF: supervisor read access in kernel mode
[ 5365.180006] #PF: error_code(0x0000) - not-present page
[ 5365.181322] PGD 8000000109dad067 P4D 8000000109dad067 PUD 107707067 PMD 0
[ 5365.183474] Oops: 0000 [#1] PREEMPT SMP PTI
[ 5365.184792] CPU: 0 PID: 22086 Comm: madvise01 Not tainted 
6.1.0-1.el8.seanjcupm.x86_64 #1
[ 5365.186572] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
BIOS 1.5.1 06/16/2021
[ 5365.188816] RIP: 0010:restrictedmem_error_page+0xc7/0x1b0
[ 5365.190081] Code: 99 00 48 8b 55 00 48 8b 02 48 8d 8a e8 fe ff ff 48 
2d 18 01 00 00 48 39 d5 0f 84 8a 00 00 00 48 8b 51 30 48 8b 92 b8 00 00 
00 <48> 8b 4a 28 4c 39 b1 d8 00 00 00 74 22 48 8b 88 18 01 00 00 48 8d
[ 5365.193984] RSP: 0018:ffff9b7343c07d80 EFLAGS: 00010206
[ 5365.195142] RAX: ffff8e5b410cfc70 RBX: 0000000000000001 RCX: 
ffff8e5b4048e580
[ 5365.196888] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 
0000000000000000
[ 5365.198399] RBP: ffff8e5b410cfd88 R08: 0000000000000000 R09: 
0000000000000000
[ 5365.200200] R10: 0000000000000000 R11: 0000000000000000 R12: 
0000000000000000
[ 5365.201843] R13: ffff8e5b410cfd80 R14: ffff8e5b47cc7618 R15: 
ffffd49d44c05080
[ 5365.203472] FS:  00007fc96de9b5c0(0000) GS:ffff8e5deda00000(0000) 
knlGS:0000000000000000
[ 5365.205485] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 5365.206791] CR2: 0000000000000028 CR3: 000000012047e002 CR4: 
0000000000170ef0
[ 5365.208131] Call Trace:
[ 5365.208752]  <TASK>
[ 5365.209229]  me_pagecache_clean+0x58/0x100
[ 5365.210196]  identify_page_state+0x84/0xd0
[ 5365.211180]  memory_failure+0x231/0x8b0
[ 5365.212148]  madvise_inject_error.cold+0x8d/0xa4
[ 5365.213317]  do_madvise+0x363/0x3a0
[ 5365.214177]  __x64_sys_madvise+0x2c/0x40
[ 5365.215159]  do_syscall_64+0x3f/0xa0
[ 5365.216016]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 5365.217130] RIP: 0033:0x7fc96d8399ab
[ 5365.217953] Code: 73 01 c3 48 8b 0d dd 54 38 00 f7 d8 64 89 01 48 83 
c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 1c 00 00 00 0f 
05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d ad 54 38 00 f7 d8 64 89 01 48
[ 5365.222323] RSP: 002b:00007fff62a99b18 EFLAGS: 00000206 ORIG_RAX: 
000000000000001c
[ 5365.224026] RAX: ffffffffffffffda RBX: 000000000041ce00 RCX: 
00007fc96d8399ab
[ 5365.225375] RDX: 0000000000000064 RSI: 000000000000a000 RDI: 
00007fc96de8e000
[ 5365.226999] RBP: 00007fc96de9b540 R08: 0000000000000001 R09: 
0000000000415c80
[ 5365.228641] R10: 0000000000000001 R11: 0000000000000206 R12: 
0000000000000008
[ 5365.230074] R13: 0000000000000000 R14: 0000000000000000 R15: 
0000000000000000

Regards,
Liam

> As for next steps, can you (handwaving all of the TDX folks) take a look at what
> I pushed and see if there's anything horrifically broken, and that it still works
> for TDX?
> 
> Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> (and I mean that).
> 
> On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> merging so that the criteria for merging are clear, and so that if the list is large
> (haven't thought much yet), the work of writing and running tests can be distributed.
> 
> Regarding downstream dependencies, before this lands, I want to pull in all the
> TDX and SNP series and see how everything fits together.  Specifically, I want to
> make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> don't miss an opportunity to make things simpler.  The patches in the SNP series to
> add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> details.  Nothing remotely major, but something that needs attention since it'll
> be uAPI.
> 
> I'm off Monday, so it'll be at least Tuesday before I make any more progress on
> my side.
> 
> Thanks!
> 

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Tue, Jan 24, 2023, Liam Merwick wrote:
> On 14/01/2023 00:37, Sean Christopherson wrote:
> > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > This patch series implements KVM guest private memory for confidential
> > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > TDX-protected guest memory, machine check can happen which can further
> > > crash the running host system, this is terrible for multi-tenant
> > > configurations. The host accesses include those from KVM userspace like
> > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > via a fd-based approach, but it can never access the guest memory
> > > content.
> > > 
> > > The patch series touches both core mm and KVM code. I appreciate
> > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > reviews are always welcome.
> > >    - 01: mm change, target for mm tree
> > >    - 02-09: KVM change, target for KVM tree
> > 
> > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > is available here:
> > 
> >    git@github.com:sean-jc/linux.git x86/upm_base_support
> > 
> > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > a WIP.
> > 
> 
> When running LTP (https://github.com/linux-test-project/ltp) on the v10
> bits (and also with Sean's branch above) I encounter the following NULL
> pointer dereference with testcases/kernel/syscalls/madvise/madvise01
> (100% reproducible).
> 
> It appears that in restrictedmem_error_page() inode->i_mapping->private_data
> is NULL
> in the list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list)
> but I don't know why.

Kirill, can you take a look?  Or pass the buck to someone who can? :-)

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Kirill A. Shutemov]

On Wed, Jan 25, 2023 at 12:20:26AM +0000, Sean Christopherson wrote:
> On Tue, Jan 24, 2023, Liam Merwick wrote:
> > On 14/01/2023 00:37, Sean Christopherson wrote:
> > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > This patch series implements KVM guest private memory for confidential
> > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > TDX-protected guest memory, machine check can happen which can further
> > > > crash the running host system, this is terrible for multi-tenant
> > > > configurations. The host accesses include those from KVM userspace like
> > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > via a fd-based approach, but it can never access the guest memory
> > > > content.
> > > > 
> > > > The patch series touches both core mm and KVM code. I appreciate
> > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > reviews are always welcome.
> > > >    - 01: mm change, target for mm tree
> > > >    - 02-09: KVM change, target for KVM tree
> > > 
> > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > is available here:
> > > 
> > >    git@github.com:sean-jc/linux.git x86/upm_base_support
> > > 
> > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > a WIP.
> > > 
> > 
> > When running LTP (https://github.com/linux-test-project/ltp) on the v10
> > bits (and also with Sean's branch above) I encounter the following NULL
> > pointer dereference with testcases/kernel/syscalls/madvise/madvise01
> > (100% reproducible).
> > 
> > It appears that in restrictedmem_error_page() inode->i_mapping->private_data
> > is NULL
> > in the list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list)
> > but I don't know why.
> 
> Kirill, can you take a look?  Or pass the buck to someone who can? :-)

The patch below should help.

diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
index 15c52301eeb9..39ada985c7c0 100644
--- a/mm/restrictedmem.c
+++ b/mm/restrictedmem.c
@@ -307,14 +307,29 @@ void restrictedmem_error_page(struct page *page, struct address_space *mapping)
 
 	spin_lock(&sb->s_inode_list_lock);
 	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
-		struct restrictedmem *rm = inode->i_mapping->private_data;
 		struct restrictedmem_notifier *notifier;
-		struct file *memfd = rm->memfd;
+		struct restrictedmem *rm;
 		unsigned long index;
+		struct file *memfd;
 
-		if (memfd->f_mapping != mapping)
+		if (atomic_read(&inode->i_count))
 			continue;
 
+		spin_lock(&inode->i_lock);
+		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+
+		rm = inode->i_mapping->private_data;
+		memfd = rm->memfd;
+
+		if (memfd->f_mapping != mapping) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+		spin_unlock(&inode->i_lock);
+
 		xa_for_each_range(&rm->bindings, index, notifier, start, end)
 			notifier->ops->error(notifier, start, end);
 		break;
-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Liam Merwick]

On 25/01/2023 12:53, Kirill A. Shutemov wrote:
> On Wed, Jan 25, 2023 at 12:20:26AM +0000, Sean Christopherson wrote:
>> On Tue, Jan 24, 2023, Liam Merwick wrote:
>>> On 14/01/2023 00:37, Sean Christopherson wrote:
>>>> On Fri, Dec 02, 2022, Chao Peng wrote:
...
>>>
>>> When running LTP (https://github.com/linux-test-project/ltp) on the v10
>>> bits (and also with Sean's branch above) I encounter the following NULL
>>> pointer dereference with testcases/kernel/syscalls/madvise/madvise01
>>> (100% reproducible).
>>>
>>> It appears that in restrictedmem_error_page() inode->i_mapping->private_data
>>> is NULL
>>> in the list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list)
>>> but I don't know why.
>>
>> Kirill, can you take a look?  Or pass the buck to someone who can? :-)
> 
> The patch below should help.

Thanks, this works for me.

Regards,
Liam

> 
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index 15c52301eeb9..39ada985c7c0 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -307,14 +307,29 @@ void restrictedmem_error_page(struct page *page, struct address_space *mapping)
>   
>   	spin_lock(&sb->s_inode_list_lock);
>   	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> -		struct restrictedmem *rm = inode->i_mapping->private_data;
>   		struct restrictedmem_notifier *notifier;
> -		struct file *memfd = rm->memfd;
> +		struct restrictedmem *rm;
>   		unsigned long index;
> +		struct file *memfd;
>   
> -		if (memfd->f_mapping != mapping)
> +		if (atomic_read(&inode->i_count))
>   			continue;
>   
> +		spin_lock(&inode->i_lock);
> +		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
> +			spin_unlock(&inode->i_lock);
> +			continue;
> +		}
> +
> +		rm = inode->i_mapping->private_data;
> +		memfd = rm->memfd;
> +
> +		if (memfd->f_mapping != mapping) {
> +			spin_unlock(&inode->i_lock);
> +			continue;
> +		}
> +		spin_unlock(&inode->i_lock);
> +
>   		xa_for_each_range(&rm->bindings, index, notifier, start, end)
>   			notifier->ops->error(notifier, start, end);
>   		break;

Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

[Chao Peng]

On Fri, Jan 13, 2023 at 11:16:27PM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 9a07380f8d3c..5aefcff614d2 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
> >  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
> >  			linfo[lpages - 1].disallow_lpage = 1;
> >  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> > +		if (kvm_slot_can_be_private(slot))
> > +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
> >  		/*
> >  		 * If the gfn and userspace address are not aligned wrt each
> >  		 * other, disable large page support for this slot.
> 
> Forgot to talk about the bug.  This code needs to handle the scenario where a
> memslot is created with existing, non-uniform attributes.  It might be a bit ugly
> (I didn't even try to write the code), but it's definitely possible, and since
> memslot updates are already slow I think it's best to handle things here.
> 
> In the meantime, I added this so we don't forget to fix it before merging.
> 
> #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> 	pr_crit_once("FIXME: Walk the memory attributes of the slot and set the mixed status appropriately");
> #endif

Here is the code to fix (based on your latest github repo).

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e552374f2357..609ff1cba9c5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2195,4 +2195,9 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
 	 KVM_X86_QUIRK_FIX_HYPERCALL_INSN |	\
 	 KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS)
 
+#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
+void kvm_memory_attributes_create_memslot(struct kvm *kvm,
+					  struct kvm_memory_slot *slot);
+#endif
+
 #endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index eda615f3951c..8833d7201e41 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7201,10 +7201,11 @@ static bool has_mixed_attrs(struct kvm *kvm, struct kvm_memory_slot *slot,
 	return false;
 }
 
-void kvm_arch_set_memory_attributes(struct kvm *kvm,
-				    struct kvm_memory_slot *slot,
-				    unsigned long attrs,
-				    gfn_t start, gfn_t end)
+static void kvm_update_lpage_mixed_flag(struct kvm *kvm,
+					struct kvm_memory_slot *slot,
+					bool set_attrs,
+					unsigned long attrs,
+					gfn_t start, gfn_t end)
 {
 	unsigned long pages, mask;
 	gfn_t gfn, gfn_end, first, last;
@@ -7231,25 +7232,53 @@ void kvm_arch_set_memory_attributes(struct kvm *kvm,
 		first = start & mask;
 		last = (end - 1) & mask;
 
-		/*
-		 * We only need to scan the head and tail page, for middle pages
-		 * we know they will not be mixed.
-		 */
+		/* head page */
 		gfn = max(first, slot->base_gfn);
 		gfn_end = min(first + pages, slot->base_gfn + slot->npages);
+		if(!set_attrs)
+			attrs = kvm_get_memory_attributes(kvm, gfn);
 		mixed = has_mixed_attrs(kvm, slot, level, attrs, gfn, gfn_end);
 		linfo_update_mixed(gfn, slot, level, mixed);
 
 		if (first == last)
 			return;
 
-		for (gfn = first + pages; gfn < last; gfn += pages)
-			linfo_update_mixed(gfn, slot, level, false);
+		/* middle pages */
+		for (gfn = first + pages; gfn < last; gfn += pages) {
+			if (set_attrs) {
+				mixed = false;
+			} else {
+				gfn_end = gfn + pages;
+				attrs = kvm_get_memory_attributes(kvm, gfn);
+				mixed = has_mixed_attrs(kvm, slot, level, attrs,
+							gfn, gfn_end);
+			}
+			linfo_update_mixed(gfn, slot, level, mixed);
+		}
 
+		/* tail page */
 		gfn = last;
 		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
+		if(!set_attrs)
+			attrs = kvm_get_memory_attributes(kvm, gfn);
 		mixed = has_mixed_attrs(kvm, slot, level, attrs, gfn, gfn_end);
 		linfo_update_mixed(gfn, slot, level, mixed);
 	}
 }
+
+void kvm_arch_set_memory_attributes(struct kvm *kvm,
+				    struct kvm_memory_slot *slot,
+				    unsigned long attrs,
+				    gfn_t start, gfn_t end)
+{
+	kvm_update_lpage_mixed_flag(kvm, slot, true, attrs, start, end);
+}
+
+void kvm_memory_attributes_create_memslot(struct kvm *kvm,
+					  struct kvm_memory_slot *slot)
+{
+
+	kvm_update_lpage_mixed_flag(kvm, slot, false, 0, slot->base_gfn,
+				    slot->base_gfn + slot->npages);
+}
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 268c3d16894d..c1074aecf2d0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12443,7 +12443,7 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
 	}
 
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
-	pr_crit_once("FIXME: Walk the memory attributes of the slot and set the mixed status appropriately");
+	kvm_memory_attributes_create_memslot(kvm, slot);
 #endif
 
 	if (kvm_page_track_create_memslot(kvm, slot, npages))

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
... 
> Strongly prefer to use similar logic to existing code that detects wraps:
> 
> 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
> 
> This is also where I'd like to add the "gfn is aligned to offset" check, though
> my brain is too fried to figure that out right now.

Used count_trailing_zeros() for this TODO, unsure we have other better
approach.

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index afc8c26fa652..fd34c5f7cd2f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -56,6 +56,7 @@
 #include <asm/processor.h>
 #include <asm/ioctl.h>
 #include <linux/uaccess.h>
+#include <linux/count_zeros.h>
 
 #include "coalesced_mmio.h"
 #include "async_pf.h"
@@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
 	return false;
 }
 
+/*
+ * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
+ */
+static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
+{
+	if (!offset)
+		return true;
+	if (!gpa)
+		return false;
+
+	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -2128,7 +2142,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (mem->flags & KVM_MEM_PRIVATE &&
 	    (mem->restrictedmem_offset & (PAGE_SIZE - 1) ||
 	     mem->restrictedmem_offset + mem->memory_size < mem->restrictedmem_offset ||
-	     0 /* TODO: require gfn be aligned with restricted offset */))
+	     !kvm_check_rmem_offset_alignment(mem->restrictedmem_offset,
+					      mem->guest_phys_addr)))
 		return -EINVAL;
 	if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_MEM_SLOTS_NUM)
 		return -EINVAL;

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Ackerley Tng]

> +static int restrictedmem_getattr(struct user_namespace *mnt_userns,
> +				 const struct path *path, struct kstat *stat,
> +				 u32 request_mask, unsigned int query_flags)
> +{
> +	struct inode *inode = d_inode(path->dentry);
> +	struct restrictedmem_data *data = inode->i_mapping->private_data;
> +	struct file *memfd = data->memfd;
> +
> +	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> +					     request_mask, query_flags);

Instead of calling shmem's getattr() with path, we should be using the
the memfd's path.

Otherwise, shmem's getattr() will use restrictedmem's inode instead of
shmem's inode. The private fields will be of the wrong type, and the
host will crash when shmem_is_huge() does SHMEM_SB(inode->i_sb)->huge),
since inode->i_sb->s_fs_info is NULL for the restrictedmem's superblock.

Here's the patch:

diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
index 37191cd9eed1..06b72d593bd8 100644
--- a/mm/restrictedmem.c
+++ b/mm/restrictedmem.c
@@ -84,7 +84,7 @@ static int restrictedmem_getattr(struct user_namespace  
*mnt_userns,
  	struct restrictedmem *rm = inode->i_mapping->private_data;
  	struct file *memfd = rm->memfd;

-	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
+	return memfd->f_inode->i_op->getattr(mnt_userns, &memfd->f_path, stat,
  					     request_mask, query_flags);
  }

> +}
> +
> +static int restrictedmem_setattr(struct user_namespace *mnt_userns,
> +				 struct dentry *dentry, struct iattr *attr)
> +{
> +	struct inode *inode = d_inode(dentry);
> +	struct restrictedmem_data *data = inode->i_mapping->private_data;
> +	struct file *memfd = data->memfd;
> +	int ret;
> +
> +	if (attr->ia_valid & ATTR_SIZE) {
> +		if (memfd->f_inode->i_size)
> +			return -EPERM;
> +
> +		if (!PAGE_ALIGNED(attr->ia_size))
> +			return -EINVAL;
> +	}
> +
> +	ret = memfd->f_inode->i_op->setattr(mnt_userns,
> +					    file_dentry(memfd), attr);
> +	return ret;
> +}
> +
> +static const struct inode_operations restrictedmem_iops = {
> +	.getattr = restrictedmem_getattr,
> +	.setattr = restrictedmem_setattr,
> +};

RE: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Wang, Wei W]

On Monday, January 30, 2023 1:26 PM, Ackerley Tng wrote:
> 
> > +static int restrictedmem_getattr(struct user_namespace *mnt_userns,
> > +				 const struct path *path, struct kstat *stat,
> > +				 u32 request_mask, unsigned int query_flags)
> {
> > +	struct inode *inode = d_inode(path->dentry);
> > +	struct restrictedmem_data *data = inode->i_mapping-
> >private_data;
> > +	struct file *memfd = data->memfd;
> > +
> > +	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> > +					     request_mask, query_flags);
> 
> Instead of calling shmem's getattr() with path, we should be using the the
> memfd's path.
> 
> Otherwise, shmem's getattr() will use restrictedmem's inode instead of
> shmem's inode. The private fields will be of the wrong type, and the host will
> crash when shmem_is_huge() does SHMEM_SB(inode->i_sb)->huge), since
> inode->i_sb->s_fs_info is NULL for the restrictedmem's superblock.
> 
> Here's the patch:
> 
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c index
> 37191cd9eed1..06b72d593bd8 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -84,7 +84,7 @@ static int restrictedmem_getattr(struct user_namespace
> *mnt_userns,
>   	struct restrictedmem *rm = inode->i_mapping->private_data;
>   	struct file *memfd = rm->memfd;
> 
> -	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> +	return memfd->f_inode->i_op->getattr(mnt_userns, &memfd-
> >f_path, stat,
>   					     request_mask, query_flags);
>   }
> 

Nice catch. I also encountered this issue during my work.
The fix can further be enforced by shmem:

index c301487be5fb..d850c0190359 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -472,8 +472,9 @@ bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
                   pgoff_t index, bool shmem_huge_force)
 {
        loff_t i_size;
+       struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

-       if (!S_ISREG(inode->i_mode))
+       if (!sbinfo || !S_ISREG(inode->i_mode))
                return false;
        if (vma && ((vma->vm_flags & VM_NOHUGEPAGE) ||
            test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)))
@@ -485,7 +486,7 @@ bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
        if (shmem_huge == SHMEM_HUGE_DENY)
                return false;

-       switch (SHMEM_SB(inode->i_sb)->huge) {
+       switch (sbinfo->huge) {
        case SHMEM_HUGE_ALWAYS:
                return true;
        case SHMEM_HUGE_WITHIN_SIZE:

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Isaku Yamahata]

On Tue, Jan 24, 2023 at 01:27:50AM +0000,
Sean Christopherson <seanjc@google.com> wrote:

> On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > On Thu, Jan 19, 2023 at 03:25:08PM +0000,
> > Sean Christopherson <seanjc@google.com> wrote:
> > 
> > > On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > > > On Sat, Jan 14, 2023 at 12:37:59AM +0000,
> > > > Sean Christopherson <seanjc@google.com> wrote:
> > > > 
> > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > > This patch series implements KVM guest private memory for confidential
> > > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > > > TDX-protected guest memory, machine check can happen which can further
> > > > > > crash the running host system, this is terrible for multi-tenant
> > > > > > configurations. The host accesses include those from KVM userspace like
> > > > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > > > via a fd-based approach, but it can never access the guest memory
> > > > > > content.
> > > > > > 
> > > > > > The patch series touches both core mm and KVM code. I appreciate
> > > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > > > reviews are always welcome.
> > > > > >   - 01: mm change, target for mm tree
> > > > > >   - 02-09: KVM change, target for KVM tree
> > > > > 
> > > > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > > > is available here:
> > > > > 
> > > > >   git@github.com:sean-jc/linux.git x86/upm_base_support
> > > > > 
> > > > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > > > a WIP.
> > > > > 
> > > > > As for next steps, can you (handwaving all of the TDX folks) take a look at what
> > > > > I pushed and see if there's anything horrifically broken, and that it still works
> > > > > for TDX?
> > > > > 
> > > > > Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> > > > > (and I mean that).
> > > > > 
> > > > > On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> > > > > (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> > > > > merging so that the criteria for merging are clear, and so that if the list is large
> > > > > (haven't thought much yet), the work of writing and running tests can be distributed.
> > > > > 
> > > > > Regarding downstream dependencies, before this lands, I want to pull in all the
> > > > > TDX and SNP series and see how everything fits together.  Specifically, I want to
> > > > > make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> > > > > don't miss an opportunity to make things simpler.  The patches in the SNP series to
> > > > > add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> > > > > details.  Nothing remotely major, but something that needs attention since it'll
> > > > > be uAPI.
> > > > 
> > > > Although I'm still debuging with TDX KVM, I needed the following.
> > > > kvm_faultin_pfn() is called without mmu_lock held.  the race to change
> > > > private/shared is handled by mmu_seq.  Maybe dedicated function only for
> > > > kvm_faultin_pfn().
> > > 
> > > Gah, you're not on the other thread where this was discussed[*].  Simply deleting
> > > the lockdep assertion is safe, for guest types that rely on the attributes to
> > > define shared vs. private, KVM rechecks the attributes under the protection of
> > > mmu_seq.
> > > 
> > > I'll get a fixed version pushed out today.
> > > 
> > > [*] https://lore.kernel.org/all/Y8gpl+LwSuSgBFks@google.com
> > 
> > Now I have tdx kvm working. I've uploaded at the followings.
> > It's rebased to v6.2-rc3.
> >         git@github.com:yamahata/linux.git tdx/upm
> >         git@github.com:yamahata/qemu.git tdx/upm
> 
> And I finally got a working, building version updated and pushed out (again to):
> 
>   git@github.com:sean-jc/linux.git x86/upm_base_support
> 

Ok, I rebased TDX part to the updated branch.
        git@github.com:yamahata/linux.git tdx/upm
        git@github.com:yamahata/qemu.git tdx/upm

Now it's v6.2-rc7 based.
qemu needs more patches to avoid registering memory slot for SMM. 
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Isaku Yamahata]

On Fri, Dec 02, 2022 at 02:13:40PM +0800,
Chao Peng <chao.p.peng@linux.intel.com> wrote:

> +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> +					   struct kvm_memory_attributes *attrs)
> +{
> +	gfn_t start, end;
> +	unsigned long i;
> +	void *entry;
> +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> +
> +	/* flags is currently not used. */
> +	if (attrs->flags)
> +		return -EINVAL;
> +	if (attrs->attributes & ~supported_attrs)
> +		return -EINVAL;
> +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> +		return -EINVAL;
> +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> +		return -EINVAL;
> +
> +	start = attrs->address >> PAGE_SHIFT;
> +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> +
> +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> +
> +	mutex_lock(&kvm->lock);
> +	for (i = start; i < end; i++)
> +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> +				    GFP_KERNEL_ACCOUNT)))
> +			break;
> +	mutex_unlock(&kvm->lock);
> +
> +	attrs->address = i << PAGE_SHIFT;
> +	attrs->size = (end - i) << PAGE_SHIFT;
> +
> +	return 0;
> +}
> +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> +

If memslot isn't private, it should return error if private attribute is set.
Something like following check is needed.

+       if (attrs->flags & KVM_MEM_PRIVATE) {
+               /* non-private memory slot doesn't allow KVM_MEM_PRIVATE */
+               for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {
+                       struct kvm_memslot_iter iter;
+                       struct kvm_memslots *slots;
+
+                       slots = __kvm_memslots(kvm, i);
+                       kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
+                               if (!kvm_slot_can_be_private(iter.slot)) {
+                                       mutex_unlock(&kvm->slots_lock);
+                                       return -EINVAL;
+                               }
+                       }
+               }
+       }
+


-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Wed, Feb 08, 2023, Isaku Yamahata wrote:
> On Fri, Dec 02, 2022 at 02:13:40PM +0800,
> Chao Peng <chao.p.peng@linux.intel.com> wrote:
> 
> > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > +					   struct kvm_memory_attributes *attrs)
> > +{
> > +	gfn_t start, end;
> > +	unsigned long i;
> > +	void *entry;
> > +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +	/* flags is currently not used. */
> > +	if (attrs->flags)
> > +		return -EINVAL;
> > +	if (attrs->attributes & ~supported_attrs)
> > +		return -EINVAL;
> > +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > +		return -EINVAL;
> > +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > +		return -EINVAL;
> > +
> > +	start = attrs->address >> PAGE_SHIFT;
> > +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> > +
> > +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > +
> > +	mutex_lock(&kvm->lock);
> > +	for (i = start; i < end; i++)
> > +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > +				    GFP_KERNEL_ACCOUNT)))
> > +			break;
> > +	mutex_unlock(&kvm->lock);
> > +
> > +	attrs->address = i << PAGE_SHIFT;
> > +	attrs->size = (end - i) << PAGE_SHIFT;
> > +
> > +	return 0;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > +
> 
> If memslot isn't private, it should return error if private attribute is set.

Why?  I'd rather keep the two things separate.  If we enforce this sort of thing
at KVM_SET_MEMORY_ATTRIBUTES, then we also have to enforce it at
KVM_SET_USER_MEMORY_REGION.

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Vlastimil Babka]

On 1/23/23 16:43, Kirill A. Shutemov wrote:
> On Thu, Dec 22, 2022 at 06:15:24PM +0000, Sean Christopherson wrote:
>> On Wed, Dec 21, 2022, Chao Peng wrote:
>> > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
>> > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
>> > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
>> > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
>> > > But for non-restricted-mem case, it is correct for KVM to decrease page's
>> > > refcount after setting up mapping in the secondary mmu, otherwise the page will
>> > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
>> > 
>> > That's true. Actually even true for restrictedmem case, most likely we
>> > will still need the kvm_release_pfn_clean() for KVM generic code. On one
>> > side, other restrictedmem users like pKVM may not require page pinning
>> > at all. On the other side, see below.
>> > 
>> > > 
>> > > So what we are expecting is: for KVM if the page comes from restricted mem, then
>> > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.
>> 
>> No, requiring the user (KVM) to guard against lack of support for page migration
>> in restricted mem is a terrible API.  It's totally fine for restricted mem to not
>> support page migration until there's a use case, but punting the problem to KVM
>> is not acceptable.  Restricted mem itself doesn't yet support page migration,
>> e.g. explosions would occur even if KVM wanted to allow migration since there is
>> no notification to invalidate existing mappings.
> 
> I tried to find a way to hook into migration path from restrictedmem. It
> is not easy because from code-mm PoV the restrictedmem page just yet
> another shmem page.
> 
> It is somewhat dubious, but I think it should be safe to override
> mapping->a_ops for the shmem mapping.
> 
> It also eliminates need in special treatment for the restrictedmem pages
> from memory-failure code.
> 
> shmem_mapping() uses ->a_ops to detect shmem mapping. Modify the
> implementation to still be true for restrictedmem pages.
> 
> Build tested only.
> 
> Any comments?
> 
> diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
> index 6fddb08f03cc..73ded3c3bad1 100644
> --- a/include/linux/restrictedmem.h
> +++ b/include/linux/restrictedmem.h
> @@ -36,8 +36,6 @@ static inline bool file_is_restrictedmem(struct file *file)
>  	return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC;
>  }
>  
> -void restrictedmem_error_page(struct page *page, struct address_space *mapping);
> -
>  #else
>  
>  static inline bool file_is_restrictedmem(struct file *file)
> @@ -45,11 +43,6 @@ static inline bool file_is_restrictedmem(struct file *file)
>  	return false;
>  }
>  
> -static inline void restrictedmem_error_page(struct page *page,
> -					    struct address_space *mapping)
> -{
> -}
> -
>  #endif /* CONFIG_RESTRICTEDMEM */
>  
>  #endif /* _LINUX_RESTRICTEDMEM_H */
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index d500ea967dc7..a4af160f37e4 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -9,6 +9,7 @@
>  #include <linux/percpu_counter.h>
>  #include <linux/xattr.h>
>  #include <linux/fs_parser.h>
> +#include <linux/magic.h>
>  
>  /* inode in-kernel data */
>  
> @@ -75,10 +76,9 @@ extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
>  		unsigned long len, unsigned long pgoff, unsigned long flags);
>  extern int shmem_lock(struct file *file, int lock, struct ucounts *ucounts);
>  #ifdef CONFIG_SHMEM
> -extern const struct address_space_operations shmem_aops;
>  static inline bool shmem_mapping(struct address_space *mapping)
>  {
> -	return mapping->a_ops == &shmem_aops;
> +	return mapping->host->i_sb->s_magic == TMPFS_MAGIC;

Alternatively just check a_ops against two possible values? Fewer chained
dereferences, no-op with !CONFIG_RESTRICTEDMEM, maybe Hugh would be less
unhappy with that.

Besides that, IIRC Michael Roth mentioned that this approach for preventing
migration would be simpler for SNP than the refcount elevation? Do I recall
right and should this be pursued then?

>  }
>  #else
>  static inline bool shmem_mapping(struct address_space *mapping)
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index f91b444e471e..145bb561ddb3 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -62,7 +62,6 @@
>  #include <linux/page-isolation.h>
>  #include <linux/pagewalk.h>
>  #include <linux/shmem_fs.h>
> -#include <linux/restrictedmem.h>
>  #include "swap.h"
>  #include "internal.h"
>  #include "ras/ras_event.h"
> @@ -941,8 +940,6 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
>  		goto out;
>  	}
>  
> -	restrictedmem_error_page(p, mapping);
> -
>  	/*
>  	 * The shmem page is kept in page cache instead of truncating
>  	 * so is expected to have an extra refcount after error-handling.
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index 15c52301eeb9..d0ca609b82cb 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -189,6 +189,51 @@ static struct file *restrictedmem_file_create(struct file *memfd)
>  	return file;
>  }
>  
> +static int restricted_error_remove_page(struct address_space *mapping,
> +					struct page *page)
> +{
> +	struct super_block *sb = restrictedmem_mnt->mnt_sb;
> +	struct inode *inode, *next;
> +	pgoff_t start, end;
> +
> +	start = page->index;
> +	end = start + thp_nr_pages(page);
> +
> +	spin_lock(&sb->s_inode_list_lock);
> +	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> +		struct restrictedmem *rm = inode->i_mapping->private_data;
> +		struct restrictedmem_notifier *notifier;
> +		struct file *memfd = rm->memfd;
> +		unsigned long index;
> +
> +		if (memfd->f_mapping != mapping)
> +			continue;
> +
> +		xa_for_each_range(&rm->bindings, index, notifier, start, end)
> +			notifier->ops->error(notifier, start, end);
> +		break;
> +	}
> +	spin_unlock(&sb->s_inode_list_lock);
> +
> +	return 0;
> +}
> +
> +#ifdef CONFIG_MIGRATION
> +static int restricted_folio(struct address_space *mapping, struct folio *dst,
> +			    struct folio *src, enum migrate_mode mode)
> +{
> +	return -EBUSY;
> +}
> +#endif
> +
> +static struct address_space_operations restricted_aops = {
> +	.dirty_folio	= noop_dirty_folio,
> +	.error_remove_page = restricted_error_remove_page,
> +#ifdef CONFIG_MIGRATION
> +	.migrate_folio	= restricted_folio,
> +#endif
> +};
> +
>  SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>  {
>  	struct file *file, *restricted_file;
> @@ -209,6 +254,8 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>  	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
>  	file->f_flags |= O_LARGEFILE;
>  
> +	file->f_mapping->a_ops = &restricted_aops;
> +
>  	restricted_file = restrictedmem_file_create(file);
>  	if (IS_ERR(restricted_file)) {
>  		err = PTR_ERR(restricted_file);
> @@ -293,31 +340,3 @@ int restrictedmem_get_page(struct file *file, pgoff_t offset,
>  }
>  EXPORT_SYMBOL_GPL(restrictedmem_get_page);
>  
> -void restrictedmem_error_page(struct page *page, struct address_space *mapping)
> -{
> -	struct super_block *sb = restrictedmem_mnt->mnt_sb;
> -	struct inode *inode, *next;
> -	pgoff_t start, end;
> -
> -	if (!shmem_mapping(mapping))
> -		return;
> -
> -	start = page->index;
> -	end = start + thp_nr_pages(page);
> -
> -	spin_lock(&sb->s_inode_list_lock);
> -	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> -		struct restrictedmem *rm = inode->i_mapping->private_data;
> -		struct restrictedmem_notifier *notifier;
> -		struct file *memfd = rm->memfd;
> -		unsigned long index;
> -
> -		if (memfd->f_mapping != mapping)
> -			continue;
> -
> -		xa_for_each_range(&rm->bindings, index, notifier, start, end)
> -			notifier->ops->error(notifier, start, end);
> -		break;
> -	}
> -	spin_unlock(&sb->s_inode_list_lock);
> -}
> diff --git a/mm/shmem.c b/mm/shmem.c
> index c1d8b8a1aa3b..3df4d95784b9 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -231,7 +231,7 @@ static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
>  }
>  
>  static const struct super_operations shmem_ops;
> -const struct address_space_operations shmem_aops;
> +static const struct address_space_operations shmem_aops;
>  static const struct file_operations shmem_file_operations;
>  static const struct inode_operations shmem_inode_operations;
>  static const struct inode_operations shmem_dir_inode_operations;
> @@ -3894,7 +3894,7 @@ static int shmem_error_remove_page(struct address_space *mapping,
>  	return 0;
>  }
>  
> -const struct address_space_operations shmem_aops = {
> +static const struct address_space_operations shmem_aops = {
>  	.writepage	= shmem_writepage,
>  	.dirty_folio	= noop_dirty_folio,
>  #ifdef CONFIG_TMPFS
> @@ -3906,7 +3906,6 @@ const struct address_space_operations shmem_aops = {
>  #endif
>  	.error_remove_page = shmem_error_remove_page,
>  };
> -EXPORT_SYMBOL(shmem_aops);
>  
>  static const struct file_operations shmem_file_operations = {
>  	.mmap		= shmem_mmap,

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Michael Roth]

On Tue, Jan 24, 2023 at 01:27:50AM +0000, Sean Christopherson wrote:
> On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > On Thu, Jan 19, 2023 at 03:25:08PM +0000,
> > Sean Christopherson <seanjc@google.com> wrote:
> > 
> > > On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > > > On Sat, Jan 14, 2023 at 12:37:59AM +0000,
> > > > Sean Christopherson <seanjc@google.com> wrote:
> > > > 
> > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > > This patch series implements KVM guest private memory for confidential
> > > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > > > TDX-protected guest memory, machine check can happen which can further
> > > > > > crash the running host system, this is terrible for multi-tenant
> > > > > > configurations. The host accesses include those from KVM userspace like
> > > > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > > > via a fd-based approach, but it can never access the guest memory
> > > > > > content.
> > > > > > 
> > > > > > The patch series touches both core mm and KVM code. I appreciate
> > > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > > > reviews are always welcome.
> > > > > >   - 01: mm change, target for mm tree
> > > > > >   - 02-09: KVM change, target for KVM tree
> > > > > 
> > > > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > > > is available here:
> > > > > 
> > > > >   git@github.com:sean-jc/linux.git x86/upm_base_support
> > > > > 
> > > > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > > > a WIP.
> > > > > 
> > > > > As for next steps, can you (handwaving all of the TDX folks) take a look at what
> > > > > I pushed and see if there's anything horrifically broken, and that it still works
> > > > > for TDX?
> > > > > 
> > > > > Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> > > > > (and I mean that).
> > > > > 
> > > > > On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> > > > > (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> > > > > merging so that the criteria for merging are clear, and so that if the list is large
> > > > > (haven't thought much yet), the work of writing and running tests can be distributed.
> > > > > 
> > > > > Regarding downstream dependencies, before this lands, I want to pull in all the
> > > > > TDX and SNP series and see how everything fits together.  Specifically, I want to
> > > > > make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> > > > > don't miss an opportunity to make things simpler.  The patches in the SNP series to
> > > > > add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> > > > > details.  Nothing remotely major, but something that needs attention since it'll
> > > > > be uAPI.
> > > > 
> > > > Although I'm still debuging with TDX KVM, I needed the following.
> > > > kvm_faultin_pfn() is called without mmu_lock held.  the race to change
> > > > private/shared is handled by mmu_seq.  Maybe dedicated function only for
> > > > kvm_faultin_pfn().
> > > 
> > > Gah, you're not on the other thread where this was discussed[*].  Simply deleting
> > > the lockdep assertion is safe, for guest types that rely on the attributes to
> > > define shared vs. private, KVM rechecks the attributes under the protection of
> > > mmu_seq.
> > > 
> > > I'll get a fixed version pushed out today.
> > > 
> > > [*] https://lore.kernel.org/all/Y8gpl+LwSuSgBFks@google.com
> > 
> > Now I have tdx kvm working. I've uploaded at the followings.
> > It's rebased to v6.2-rc3.
> >         git@github.com:yamahata/linux.git tdx/upm
> >         git@github.com:yamahata/qemu.git tdx/upm
> 
> And I finally got a working, building version updated and pushed out (again to):
> 
>   git@github.com:sean-jc/linux.git x86/upm_base_support
> 
> Took longer than expected to get the memslot restrictions sussed out.  I'm done
> working on the code for now, my plan is to come back to it+TDX+SNP in 2-3 weeks
> to resolves any remaining todos (that no one else tackles) and to do the whole
> "merge the world" excersise.
> 
> > kvm_mmu_do_page_fault() needs the following change.
> > kvm_mem_is_private() queries mem_attr_array.  kvm_faultin_pfn() also uses
> > kvm_mem_is_private(). So the shared-private check in kvm_faultin_pfn() doesn't
> > make sense. This change would belong to TDX KVM patches, though.
> 
> Yeah, SNP needs similar treatment.  Sorting that out is high up on the todo list.

Hi Sean,

We've rebased the SEV+SNP support onto your updated UPM base support
tree and things seem to be working okay, but we needed some fixups on
top of the base support get things working, along with 1 workaround
for an issue that hasn't been root-caused yet:

  https://github.com/mdroth/linux/commits/upmv10b-host-snp-v8-wip

  *stash (upm_base_support): mm: restrictedmem: Kirill's pinning implementation
  *workaround (use_base_support): mm: restrictedmem: loosen exclusivity check
  *fixup (upm_base_support): KVM: use inclusive ranges for restrictedmem binding/unbinding
  *fixup (upm_base_support): mm: restrictedmem: use inclusive ranges for issuing invalidations
  *fixup (upm_base_support): KVM: fix restrictedmem GFN range calculations
  *fixup (upm_base_support): KVM: selftests: CoCo compilation fixes

We plan to post an updated RFC for v8 soon, but also wanted to share
the staging tree in case you end up looking at the UPM integration aspects
before then.

-Mike

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Michael Roth]

On Mon, Jan 23, 2023 at 06:43:34PM +0300, Kirill A. Shutemov wrote:
> On Thu, Dec 22, 2022 at 06:15:24PM +0000, Sean Christopherson wrote:
> > On Wed, Dec 21, 2022, Chao Peng wrote:
> > > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > > > refcount after setting up mapping in the secondary mmu, otherwise the page will
> > > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> > > 
> > > That's true. Actually even true for restrictedmem case, most likely we
> > > will still need the kvm_release_pfn_clean() for KVM generic code. On one
> > > side, other restrictedmem users like pKVM may not require page pinning
> > > at all. On the other side, see below.
> > > 
> > > > 
> > > > So what we are expecting is: for KVM if the page comes from restricted mem, then
> > > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should.
> > 
> > No, requiring the user (KVM) to guard against lack of support for page migration
> > in restricted mem is a terrible API.  It's totally fine for restricted mem to not
> > support page migration until there's a use case, but punting the problem to KVM
> > is not acceptable.  Restricted mem itself doesn't yet support page migration,
> > e.g. explosions would occur even if KVM wanted to allow migration since there is
> > no notification to invalidate existing mappings.
> 
> I tried to find a way to hook into migration path from restrictedmem. It
> is not easy because from code-mm PoV the restrictedmem page just yet
> another shmem page.
> 
> It is somewhat dubious, but I think it should be safe to override
> mapping->a_ops for the shmem mapping.
> 
> It also eliminates need in special treatment for the restrictedmem pages
> from memory-failure code.
> 
> shmem_mapping() uses ->a_ops to detect shmem mapping. Modify the
> implementation to still be true for restrictedmem pages.
> 
> Build tested only.
> 
> Any comments?

Hi Kirill,

We've been testing your approach to handle pinning for the SNP+UPM
implementation and haven't noticed any problems so far:

  (based on top of Sean's updated UPM v10 tree)
  https://github.com/mdroth/linux/commit/f780033e6812a01f8732060605d941474fee2bd6

Prior to your patch we also tried elevating refcount via
restrictedmem_get_page() for cases where shmem_get_folio(..., SGP_NOALLOC)
indicates the page hasn't been allocated yet, and that approach also
seems to work, but there are potential races and other ugliness that
make your approach seem a lot cleaner.

-Mike

> 
> diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
> index 6fddb08f03cc..73ded3c3bad1 100644
> --- a/include/linux/restrictedmem.h
> +++ b/include/linux/restrictedmem.h
> @@ -36,8 +36,6 @@ static inline bool file_is_restrictedmem(struct file *file)
>  	return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC;
>  }
>  
> -void restrictedmem_error_page(struct page *page, struct address_space *mapping);
> -
>  #else
>  
>  static inline bool file_is_restrictedmem(struct file *file)
> @@ -45,11 +43,6 @@ static inline bool file_is_restrictedmem(struct file *file)
>  	return false;
>  }
>  
> -static inline void restrictedmem_error_page(struct page *page,
> -					    struct address_space *mapping)
> -{
> -}
> -
>  #endif /* CONFIG_RESTRICTEDMEM */
>  
>  #endif /* _LINUX_RESTRICTEDMEM_H */
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index d500ea967dc7..a4af160f37e4 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -9,6 +9,7 @@
>  #include <linux/percpu_counter.h>
>  #include <linux/xattr.h>
>  #include <linux/fs_parser.h>
> +#include <linux/magic.h>
>  
>  /* inode in-kernel data */
>  
> @@ -75,10 +76,9 @@ extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
>  		unsigned long len, unsigned long pgoff, unsigned long flags);
>  extern int shmem_lock(struct file *file, int lock, struct ucounts *ucounts);
>  #ifdef CONFIG_SHMEM
> -extern const struct address_space_operations shmem_aops;
>  static inline bool shmem_mapping(struct address_space *mapping)
>  {
> -	return mapping->a_ops == &shmem_aops;
> +	return mapping->host->i_sb->s_magic == TMPFS_MAGIC;
>  }
>  #else
>  static inline bool shmem_mapping(struct address_space *mapping)
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index f91b444e471e..145bb561ddb3 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -62,7 +62,6 @@
>  #include <linux/page-isolation.h>
>  #include <linux/pagewalk.h>
>  #include <linux/shmem_fs.h>
> -#include <linux/restrictedmem.h>
>  #include "swap.h"
>  #include "internal.h"
>  #include "ras/ras_event.h"
> @@ -941,8 +940,6 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
>  		goto out;
>  	}
>  
> -	restrictedmem_error_page(p, mapping);
> -
>  	/*
>  	 * The shmem page is kept in page cache instead of truncating
>  	 * so is expected to have an extra refcount after error-handling.
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index 15c52301eeb9..d0ca609b82cb 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -189,6 +189,51 @@ static struct file *restrictedmem_file_create(struct file *memfd)
>  	return file;
>  }
>  
> +static int restricted_error_remove_page(struct address_space *mapping,
> +					struct page *page)
> +{
> +	struct super_block *sb = restrictedmem_mnt->mnt_sb;
> +	struct inode *inode, *next;
> +	pgoff_t start, end;
> +
> +	start = page->index;
> +	end = start + thp_nr_pages(page);
> +
> +	spin_lock(&sb->s_inode_list_lock);
> +	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> +		struct restrictedmem *rm = inode->i_mapping->private_data;
> +		struct restrictedmem_notifier *notifier;
> +		struct file *memfd = rm->memfd;
> +		unsigned long index;
> +
> +		if (memfd->f_mapping != mapping)
> +			continue;
> +
> +		xa_for_each_range(&rm->bindings, index, notifier, start, end)
> +			notifier->ops->error(notifier, start, end);
> +		break;
> +	}
> +	spin_unlock(&sb->s_inode_list_lock);
> +
> +	return 0;
> +}
> +
> +#ifdef CONFIG_MIGRATION
> +static int restricted_folio(struct address_space *mapping, struct folio *dst,
> +			    struct folio *src, enum migrate_mode mode)
> +{
> +	return -EBUSY;
> +}
> +#endif
> +
> +static struct address_space_operations restricted_aops = {
> +	.dirty_folio	= noop_dirty_folio,
> +	.error_remove_page = restricted_error_remove_page,
> +#ifdef CONFIG_MIGRATION
> +	.migrate_folio	= restricted_folio,
> +#endif
> +};
> +
>  SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>  {
>  	struct file *file, *restricted_file;
> @@ -209,6 +254,8 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>  	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
>  	file->f_flags |= O_LARGEFILE;
>  
> +	file->f_mapping->a_ops = &restricted_aops;
> +
>  	restricted_file = restrictedmem_file_create(file);
>  	if (IS_ERR(restricted_file)) {
>  		err = PTR_ERR(restricted_file);
> @@ -293,31 +340,3 @@ int restrictedmem_get_page(struct file *file, pgoff_t offset,
>  }
>  EXPORT_SYMBOL_GPL(restrictedmem_get_page);
>  
> -void restrictedmem_error_page(struct page *page, struct address_space *mapping)
> -{
> -	struct super_block *sb = restrictedmem_mnt->mnt_sb;
> -	struct inode *inode, *next;
> -	pgoff_t start, end;
> -
> -	if (!shmem_mapping(mapping))
> -		return;
> -
> -	start = page->index;
> -	end = start + thp_nr_pages(page);
> -
> -	spin_lock(&sb->s_inode_list_lock);
> -	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> -		struct restrictedmem *rm = inode->i_mapping->private_data;
> -		struct restrictedmem_notifier *notifier;
> -		struct file *memfd = rm->memfd;
> -		unsigned long index;
> -
> -		if (memfd->f_mapping != mapping)
> -			continue;
> -
> -		xa_for_each_range(&rm->bindings, index, notifier, start, end)
> -			notifier->ops->error(notifier, start, end);
> -		break;
> -	}
> -	spin_unlock(&sb->s_inode_list_lock);
> -}
> diff --git a/mm/shmem.c b/mm/shmem.c
> index c1d8b8a1aa3b..3df4d95784b9 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -231,7 +231,7 @@ static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
>  }
>  
>  static const struct super_operations shmem_ops;
> -const struct address_space_operations shmem_aops;
> +static const struct address_space_operations shmem_aops;
>  static const struct file_operations shmem_file_operations;
>  static const struct inode_operations shmem_inode_operations;
>  static const struct inode_operations shmem_dir_inode_operations;
> @@ -3894,7 +3894,7 @@ static int shmem_error_remove_page(struct address_space *mapping,
>  	return 0;
>  }
>  
> -const struct address_space_operations shmem_aops = {
> +static const struct address_space_operations shmem_aops = {
>  	.writepage	= shmem_writepage,
>  	.dirty_folio	= noop_dirty_folio,
>  #ifdef CONFIG_TMPFS
> @@ -3906,7 +3906,6 @@ const struct address_space_operations shmem_aops = {
>  #endif
>  	.error_remove_page = shmem_error_remove_page,
>  };
> -EXPORT_SYMBOL(shmem_aops);
>  
>  static const struct file_operations shmem_file_operations = {
>  	.mmap		= shmem_mmap,
> -- 
>   Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Vlastimil Babka]

On 1/23/23 16:18, Kirill A. Shutemov wrote:
> On Mon, Jan 23, 2023 at 03:03:45PM +0100, Vlastimil Babka wrote:
>> On 12/22/22 01:37, Huang, Kai wrote:
>> >>> I argue that this page pinning (or page migration prevention) is not
>> >>> tied to where the page comes from, instead related to how the page will
>> >>> be used. Whether the page is restrictedmem backed or GUP() backed, once
>> >>> it's used by current version of TDX then the page pinning is needed. So
>> >>> such page migration prevention is really TDX thing, even not KVM generic
>> >>> thing (that's why I think we don't need change the existing logic of
>> >>> kvm_release_pfn_clean()). 
>> >>>
>> > This essentially boils down to who "owns" page migration handling, and sadly,
>> > page migration is kinda "owned" by the core-kernel, i.e. KVM cannot handle page
>> > migration by itself -- it's just a passive receiver.
>> > 
>> > For normal pages, page migration is totally done by the core-kernel (i.e. it
>> > unmaps page from VMA, allocates a new page, and uses migrate_pape() or a_ops-
>> >> migrate_page() to actually migrate the page).
>> > In the sense of TDX, conceptually it should be done in the same way. The more
>> > important thing is: yes KVM can use get_page() to prevent page migration, but
>> > when KVM wants to support it, KVM cannot just remove get_page(), as the core-
>> > kernel will still just do migrate_page() which won't work for TDX (given
>> > restricted_memfd doesn't have a_ops->migrate_page() implemented).
>> > 
>> > So I think the restricted_memfd filesystem should own page migration handling,
>> > (i.e. by implementing a_ops->migrate_page() to either just reject page migration
>> > or somehow support it).
>> 
>> While this thread seems to be settled on refcounts already, just wanted
>> to point out that it wouldn't be ideal to prevent migrations by
>> a_ops->migrate_page() rejecting them. It would mean cputime wasted (i.e.
>> by memory compaction) by isolating the pages for migration and then
>> releasing them after the callback rejects it (at least we wouldn't waste
>> time creating and undoing migration entries in the userspace page tables
>> as there's no mmap). Elevated refcount on the other hand is detected
>> very early in compaction so no isolation is attempted, so from that
>> aspect it's optimal.
> 
> Hm. Do we need a new hook in a_ops to check if the page is migratable
> before going with longer path to migrate_page().
> 
> Or maybe add AS_UNMOVABLE?

AS_UNMOVABLE should indeed allow a test in e.g. compaction to descide that
the page is not worth isolating in the first place.

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Isaku Yamahata]

On Fri, Feb 10, 2023 at 12:35:30AM +0000,
Sean Christopherson <seanjc@google.com> wrote:

> On Wed, Feb 08, 2023, Isaku Yamahata wrote:
> > On Fri, Dec 02, 2022 at 02:13:40PM +0800,
> > Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > 
> > > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > > +					   struct kvm_memory_attributes *attrs)
> > > +{
> > > +	gfn_t start, end;
> > > +	unsigned long i;
> > > +	void *entry;
> > > +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > > +
> > > +	/* flags is currently not used. */
> > > +	if (attrs->flags)
> > > +		return -EINVAL;
> > > +	if (attrs->attributes & ~supported_attrs)
> > > +		return -EINVAL;
> > > +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > > +		return -EINVAL;
> > > +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > > +		return -EINVAL;
> > > +
> > > +	start = attrs->address >> PAGE_SHIFT;
> > > +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> > > +
> > > +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > > +
> > > +	mutex_lock(&kvm->lock);
> > > +	for (i = start; i < end; i++)
> > > +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > > +				    GFP_KERNEL_ACCOUNT)))
> > > +			break;
> > > +	mutex_unlock(&kvm->lock);
> > > +
> > > +	attrs->address = i << PAGE_SHIFT;
> > > +	attrs->size = (end - i) << PAGE_SHIFT;
> > > +
> > > +	return 0;
> > > +}
> > > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > > +
> > 
> > If memslot isn't private, it should return error if private attribute is set.
> 
> Why?  I'd rather keep the two things separate.  If we enforce this sort of thing
> at KVM_SET_MEMORY_ATTRIBUTES, then we also have to enforce it at
> KVM_SET_USER_MEMORY_REGION.

For device assignment via shared GPA, non-private memory slot needs to be
allowed.
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Mon, Feb 13, 2023, Isaku Yamahata wrote:
> On Fri, Feb 10, 2023 at 12:35:30AM +0000,
> Sean Christopherson <seanjc@google.com> wrote:
> 
> > On Wed, Feb 08, 2023, Isaku Yamahata wrote:
> > > On Fri, Dec 02, 2022 at 02:13:40PM +0800,
> > > Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > > 
> > > > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > > > +					   struct kvm_memory_attributes *attrs)
> > > > +{
> > > > +	gfn_t start, end;
> > > > +	unsigned long i;
> > > > +	void *entry;
> > > > +	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > > > +
> > > > +	/* flags is currently not used. */
> > > > +	if (attrs->flags)
> > > > +		return -EINVAL;
> > > > +	if (attrs->attributes & ~supported_attrs)
> > > > +		return -EINVAL;
> > > > +	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > > > +		return -EINVAL;
> > > > +	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > > > +		return -EINVAL;
> > > > +
> > > > +	start = attrs->address >> PAGE_SHIFT;
> > > > +	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> > > > +
> > > > +	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > > > +
> > > > +	mutex_lock(&kvm->lock);
> > > > +	for (i = start; i < end; i++)
> > > > +		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > > > +				    GFP_KERNEL_ACCOUNT)))
> > > > +			break;
> > > > +	mutex_unlock(&kvm->lock);
> > > > +
> > > > +	attrs->address = i << PAGE_SHIFT;
> > > > +	attrs->size = (end - i) << PAGE_SHIFT;
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > > > +
> > > 
> > > If memslot isn't private, it should return error if private attribute is set.
> > 
> > Why?  I'd rather keep the two things separate.  If we enforce this sort of thing
> > at KVM_SET_MEMORY_ATTRIBUTES, then we also have to enforce it at
> > KVM_SET_USER_MEMORY_REGION.
> 
> For device assignment via shared GPA, non-private memory slot needs to be
> allowed.

That doesn't say anything about why setting attributes needs to poke into the
memslot.  The page fault path already kicks out to userspace if there's a
discrepancy between the attributes and the memslot, why is that insufficient?

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Mike Rapoport]

Hi,

On Fri, Dec 02, 2022 at 02:13:38PM +0800, Chao Peng wrote:
> This patch series implements KVM guest private memory for confidential
> computing scenarios like Intel TDX[1]. If a TDX host accesses
> TDX-protected guest memory, machine check can happen which can further
> crash the running host system, this is terrible for multi-tenant
> configurations. The host accesses include those from KVM userspace like
> QEMU. This series addresses KVM userspace induced crash by introducing
> new mm and KVM interfaces so KVM userspace can still manage guest memory
> via a fd-based approach, but it can never access the guest memory
> content.

Sorry for jumping late.

Unless I'm missing something, hibernation will also cause an machine check
when there is TDX-protected memory in the system. When the hibernation
creates memory snapshot it essentially walks all physical pages and saves
their contents, so for TDX memory this will trigger machine check, right?
 
>  Documentation/virt/kvm/api.rst         | 125 ++++++-
>  arch/x86/entry/syscalls/syscall_32.tbl |   1 +
>  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
>  arch/x86/include/asm/kvm_host.h        |   9 +
>  arch/x86/kvm/Kconfig                   |   3 +
>  arch/x86/kvm/mmu/mmu.c                 | 205 ++++++++++-
>  arch/x86/kvm/mmu/mmu_internal.h        |  14 +-
>  arch/x86/kvm/mmu/mmutrace.h            |   1 +
>  arch/x86/kvm/mmu/tdp_mmu.c             |   2 +-
>  arch/x86/kvm/x86.c                     |  17 +-
>  include/linux/kvm_host.h               | 103 +++++-
>  include/linux/restrictedmem.h          |  71 ++++
>  include/linux/syscalls.h               |   1 +
>  include/uapi/asm-generic/unistd.h      |   5 +-
>  include/uapi/linux/kvm.h               |  53 +++
>  include/uapi/linux/magic.h             |   1 +
>  kernel/sys_ni.c                        |   3 +
>  mm/Kconfig                             |   4 +
>  mm/Makefile                            |   1 +
>  mm/memory-failure.c                    |   3 +
>  mm/restrictedmem.c                     | 318 +++++++++++++++++
>  virt/kvm/Kconfig                       |   6 +
>  virt/kvm/kvm_main.c                    | 469 +++++++++++++++++++++----
>  23 files changed, 1323 insertions(+), 93 deletions(-)
>  create mode 100644 include/linux/restrictedmem.h
>  create mode 100644 mm/restrictedmem.c

-- 
Sincerely yours,
Mike.

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[David Hildenbrand]

On 16.02.23 06:13, Mike Rapoport wrote:
> Hi,
> 
> On Fri, Dec 02, 2022 at 02:13:38PM +0800, Chao Peng wrote:
>> This patch series implements KVM guest private memory for confidential
>> computing scenarios like Intel TDX[1]. If a TDX host accesses
>> TDX-protected guest memory, machine check can happen which can further
>> crash the running host system, this is terrible for multi-tenant
>> configurations. The host accesses include those from KVM userspace like
>> QEMU. This series addresses KVM userspace induced crash by introducing
>> new mm and KVM interfaces so KVM userspace can still manage guest memory
>> via a fd-based approach, but it can never access the guest memory
>> content.
> 
> Sorry for jumping late.
> 
> Unless I'm missing something, hibernation will also cause an machine check
> when there is TDX-protected memory in the system. When the hibernation
> creates memory snapshot it essentially walks all physical pages and saves
> their contents, so for TDX memory this will trigger machine check, right?

I recall bringing that up in the past (also memory access due to kdump, 
/prov/kcore) and was told that the main focus for now is preventing 
unprivileged users from crashing the system, that is, not mapping such 
memory into user space (e.g., QEMU). In the long run, we'll want to 
handle such pages also properly in the other events where the kernel 
might access them.

-- 
Thanks,

David / dhildenb

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Nikunj A. Dadhania]

> +static struct file *restrictedmem_file_create(struct file *memfd)
> +{
> +	struct restrictedmem_data *data;
> +	struct address_space *mapping;
> +	struct inode *inode;
> +	struct file *file;
> +
> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return ERR_PTR(-ENOMEM);
> +
> +	data->memfd = memfd;
> +	mutex_init(&data->lock);
> +	INIT_LIST_HEAD(&data->notifiers);
> +
> +	inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
> +	if (IS_ERR(inode)) {
> +		kfree(data);
> +		return ERR_CAST(inode);
> +	}

alloc_anon_inode() uses new_pseudo_inode() to get the inode. As per the comment, new inode 
is not added to the superblock s_inodes list.

/**
 *	new_inode_pseudo 	- obtain an inode
 *	@sb: superblock
 *
 *	Allocates a new inode for given superblock.
 *	Inode wont be chained in superblock s_inodes list
 *	This means :
 *	- fs can't be unmount
 *	- quotas, fsnotify, writeback can't work
 */

So the restrictedmem_error_page will not find the inode as it was never added to the s_inodes list.

We might need to add the inode after allocating.

	inode_sb_list_add(inode);

> +void restrictedmem_error_page(struct page *page, struct address_space *mapping)
> +{
> +	struct super_block *sb = restrictedmem_mnt->mnt_sb;
> +	struct inode *inode, *next;
> +
> +	if (!shmem_mapping(mapping))
> +		return;
> +
> +	spin_lock(&sb->s_inode_list_lock);
> +	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> +		struct restrictedmem_data *data = inode->i_mapping->private_data;
> +		struct file *memfd = data->memfd;
> +
> +		if (memfd->f_mapping == mapping) {
> +			pgoff_t start, end;
> +
> +			spin_unlock(&sb->s_inode_list_lock);
> +
> +			start = page->index;
> +			end = start + thp_nr_pages(page);
> +			restrictedmem_notifier_error(data, start, end);
> +			return;
> +		}
> +	}
> +	spin_unlock(&sb->s_inode_list_lock);
> +}

Regards
Nikunj

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Chao Peng]

> Hi Sean,
> 
> We've rebased the SEV+SNP support onto your updated UPM base support
> tree and things seem to be working okay, but we needed some fixups on
> top of the base support get things working, along with 1 workaround
> for an issue that hasn't been root-caused yet:
> 
>   https://github.com/mdroth/linux/commits/upmv10b-host-snp-v8-wip
> 
>   *stash (upm_base_support): mm: restrictedmem: Kirill's pinning implementation
>   *workaround (use_base_support): mm: restrictedmem: loosen exclusivity check

What I'm seeing is Slot#3 gets added first and then deleted. When it's
gets added, Slot#0 already has the same range bound to restrictedmem so
trigger the exclusive check. This check is exactly the current code for.

>   *fixup (upm_base_support): KVM: use inclusive ranges for restrictedmem binding/unbinding
>   *fixup (upm_base_support): mm: restrictedmem: use inclusive ranges for issuing invalidations

As many kernel APIs treat 'end' as exclusive, I would rather keep using
exclusive 'end' for these APIs(restrictedmem_bind/restrictedmem_unbind
and notifier callbacks) but fix it internally in the restrictedmem. E.g.
all the places where xarray API needs a 'last'/'max' we use 'end - 1'.
See below for the change.

>   *fixup (upm_base_support): KVM: fix restrictedmem GFN range calculations

Subtracting slot->restrictedmem.index for start/end in
restrictedmem_get_gfn_range() is the correct fix.

>   *fixup (upm_base_support): KVM: selftests: CoCo compilation fixes
> 
> We plan to post an updated RFC for v8 soon, but also wanted to share
> the staging tree in case you end up looking at the UPM integration aspects
> before then.
> 
> -Mike

This is the restrictedmem fix to solve 'end' being stored and checked in xarray:

--- a/mm/restrictedmem.c
+++ b/mm/restrictedmem.c
@@ -46,12 +46,12 @@ static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
         */
        down_read(&rm->lock);
 
-       xa_for_each_range(&rm->bindings, index, notifier, start, end)
+       xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
                notifier->ops->invalidate_start(notifier, start, end);
 
        ret = memfd->f_op->fallocate(memfd, mode, offset, len);
 
-       xa_for_each_range(&rm->bindings, index, notifier, start, end)
+       xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
                notifier->ops->invalidate_end(notifier, start, end);
 
        up_read(&rm->lock);
@@ -224,7 +224,7 @@ static int restricted_error_remove_page(struct address_space *mapping,
                }
                spin_unlock(&inode->i_lock);
 
-               xa_for_each_range(&rm->bindings, index, notifier, start, end)
+               xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
                        notifier->ops->error(notifier, start, end);
                break;
        }
@@ -301,11 +301,12 @@ int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
                if (exclusive != rm->exclusive)
                        goto out_unlock;
 
-               if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
+               if (exclusive &&
+                   xa_find(&rm->bindings, &start, end - 1, XA_PRESENT))
                        goto out_unlock;
        }
 
-       xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);
+       xa_store_range(&rm->bindings, start, end - 1, notifier, GFP_KERNEL);
        rm->exclusive = exclusive;
        ret = 0;
 out_unlock:
@@ -320,7 +321,7 @@ void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
        struct restrictedmem *rm = file->f_mapping->private_data;
 
        down_write(&rm->lock);
-       xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
+       xa_store_range(&rm->bindings, start, end - 1, NULL, GFP_KERNEL);
        synchronize_rcu();
        up_write(&rm->lock);
 }

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Alexey Kardashevskiy]

On 14/1/23 08:54, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
>> The system call is currently wired up for x86 arch.
> 
> Building on other architectures (except for arm64 for some reason) yields:
> 
>    CALL    /.../scripts/checksyscalls.sh
>    <stdin>:1565:2: warning: #warning syscall memfd_restricted not implemented [-Wcpp]
> 
> Do we care?  It's the only such warning, which makes me think we either need to
> wire this up for all architectures, or explicitly document that it's unsupported.
> 
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
>> ---
> 
> ...
> 
>> diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
>> new file mode 100644
>> index 000000000000..c2700c5daa43
>> --- /dev/null
>> +++ b/include/linux/restrictedmem.h
>> @@ -0,0 +1,71 @@
>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>> +#ifndef _LINUX_RESTRICTEDMEM_H
> 
> Missing
> 
>   #define _LINUX_RESTRICTEDMEM_H
> 
> which causes fireworks if restrictedmem.h is included more than once.
> 
>> +#include <linux/file.h>
>> +#include <linux/magic.h>
>> +#include <linux/pfn_t.h>
> 
> ...
> 
>> +static inline int restrictedmem_get_page(struct file *file, pgoff_t offset,
>> +					 struct page **pagep, int *order)
>> +{
>> +	return -1;
> 
> This should be a proper -errno, though in the current incarnation of things it's
> a moot point because no stub is needed.  KVM can (and should) easily provide its
> own stub for this one.
> 
>> +}
>> +
>> +static inline bool file_is_restrictedmem(struct file *file)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline void restrictedmem_error_page(struct page *page,
>> +					    struct address_space *mapping)
>> +{
>> +}
>> +
>> +#endif /* CONFIG_RESTRICTEDMEM */
>> +
>> +#endif /* _LINUX_RESTRICTEDMEM_H */
> 
> ...
> 
>> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
>> new file mode 100644
>> index 000000000000..56953c204e5c
>> --- /dev/null
>> +++ b/mm/restrictedmem.c
>> @@ -0,0 +1,318 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +#include "linux/sbitmap.h"
>> +#include <linux/pagemap.h>
>> +#include <linux/pseudo_fs.h>
>> +#include <linux/shmem_fs.h>
>> +#include <linux/syscalls.h>
>> +#include <uapi/linux/falloc.h>
>> +#include <uapi/linux/magic.h>
>> +#include <linux/restrictedmem.h>
>> +
>> +struct restrictedmem_data {
> 
> Any objection to simply calling this "restrictedmem"?  And then using either "rm"
> or "rmem" for local variable names?  I kept reading "data" as the underyling data
> being written to the page, as opposed to the metadata describing the restrictedmem
> instance.
> 
>> +	struct mutex lock;
>> +	struct file *memfd;
>> +	struct list_head notifiers;
>> +};
>> +
>> +static void restrictedmem_invalidate_start(struct restrictedmem_data *data,
>> +					   pgoff_t start, pgoff_t end)
>> +{
>> +	struct restrictedmem_notifier *notifier;
>> +
>> +	mutex_lock(&data->lock);
> 
> This can be a r/w semaphore instead of a mutex, that way punching holes at multiple
> points in the file can at least run the notifiers in parallel.  The actual allocation
> by shmem will still be serialized, but I think it's worth the simple optimization
> since zapping and flushing in KVM may be somewhat slow.
> 
>> +	list_for_each_entry(notifier, &data->notifiers, list) {
>> +		notifier->ops->invalidate_start(notifier, start, end);
> 
> Two major design issues that we overlooked long ago:
> 
>    1. Blindly invoking notifiers will not scale.  E.g. if userspace configures a
>       VM with a large number of convertible memslots that are all backed by a
>       single large restrictedmem instance, then converting a single page will
>       result in a linear walk through all memslots.  I don't expect anyone to
>       actually do something silly like that, but I also never expected there to be
>       a legitimate usecase for thousands of memslots.
> 
>    2. This approach fails to provide the ability for KVM to ensure a guest has
>       exclusive access to a page.  As discussed in the past, the kernel can rely
>       on hardware (and maybe ARM's pKVM implementation?) for those guarantees, but
>       only for SNP and TDX VMs.  For VMs where userspace is trusted to some extent,
>       e.g. SEV, there is value in ensuring a 1:1 association.
> 
>       And probably more importantly, relying on hardware for SNP and TDX yields a
>       poor ABI and complicates KVM's internals.  If the kernel doesn't guarantee a
>       page is exclusive to a guest, i.e. if userspace can hand out the same page
>       from a restrictedmem instance to multiple VMs, then failure will occur only
>       when KVM tries to assign the page to the second VM.  That will happen deep
>       in KVM, which means KVM needs to gracefully handle such errors, and it means
>       that KVM's ABI effectively allows plumbing garbage into its memslots.
> 
> Rather than use a simple list of notifiers, this appears to be yet another
> opportunity to use an xarray.  Supporting sharing of restrictedmem will be
> non-trivial, but IMO we should punt that to the future since it's still unclear
> exactly how sharing will work.
> 
> An xarray will solve #1 by notifying only the consumers (memslots) that are bound
> to the affected range.
> 
> And for #2, it's relatively straightforward (knock wood) to detect existing
> entries, i.e. if the user wants exclusive access to memory, then the bind operation
> can be reject if there's an existing entry.
> 
> VERY lightly tested code snippet at the bottom (will provide link to fully worked
> code in cover letter).
> 
> 
>> +static long restrictedmem_punch_hole(struct restrictedmem_data *data, int mode,
>> +				     loff_t offset, loff_t len)
>> +{
>> +	int ret;
>> +	pgoff_t start, end;
>> +	struct file *memfd = data->memfd;
>> +
>> +	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
>> +		return -EINVAL;
>> +
>> +	start = offset >> PAGE_SHIFT;
>> +	end = (offset + len) >> PAGE_SHIFT;
>> +
>> +	restrictedmem_invalidate_start(data, start, end);
>> +	ret = memfd->f_op->fallocate(memfd, mode, offset, len);
>> +	restrictedmem_invalidate_end(data, start, end);
> 
> The lock needs to be end for the entire duration of the hole punch, i.e. needs to
> be taken before invalidate_start() and released after invalidate_end().  If a user
> (un)binds/(un)registers after invalidate_state(), it will see an unpaired notification,
> e.g. could leave KVM with incorrect notifier counts.
> 
>> +
>> +	return ret;
>> +}
> 
> What I ended up with for an xarray-based implementation.  I'm very flexible on
> names and whatnot, these are just what made sense to me.
> 
> static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
> 				     loff_t offset, loff_t len)
> {
> 	struct restrictedmem_notifier *notifier;
> 	struct file *memfd = rm->memfd;
> 	unsigned long index;
> 	pgoff_t start, end;
> 	int ret;
> 
> 	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> 		return -EINVAL;
> 
> 	start = offset >> PAGE_SHIFT;
> 	end = (offset + len) >> PAGE_SHIFT;
> 
> 	/*
> 	 * Bindings must stable across invalidation to ensure the start+end
> 	 * are balanced.
> 	 */
> 	down_read(&rm->lock);
> 
> 	xa_for_each_range(&rm->bindings, index, notifier, start, end)
> 		notifier->ops->invalidate_start(notifier, start, end);
> 
> 	ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> 
> 	xa_for_each_range(&rm->bindings, index, notifier, start, end)
> 		notifier->ops->invalidate_end(notifier, start, end);
> 
> 	up_read(&rm->lock);
> 
> 	return ret;
> }
> 
> int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
> 		       struct restrictedmem_notifier *notifier, bool exclusive)
> {
> 	struct restrictedmem *rm = file->f_mapping->private_data;
> 	int ret = -EINVAL;
> 
> 	down_write(&rm->lock);
> 
> 	/* Non-exclusive mappings are not yet implemented. */
> 	if (!exclusive)
> 		goto out_unlock;
> 
> 	if (!xa_empty(&rm->bindings)) {
> 		if (exclusive != rm->exclusive)
> 			goto out_unlock;
> 
> 		if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
> 			goto out_unlock;
> 	}
> 
> 	xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);


|| ld: mm/restrictedmem.o: in function `restrictedmem_bind':
mm/restrictedmem.c|295| undefined reference to `xa_store_range'


This is missing:
===
diff --git a/mm/Kconfig b/mm/Kconfig
index f952d0172080..03aca542c0da 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1087,6 +1087,7 @@ config SECRETMEM
  config RESTRICTEDMEM
         bool
         depends on TMPFS
+       select XARRAY_MULTI
===

Thanks,



> 	rm->exclusive = exclusive;
> 	ret = 0;
> out_unlock:
> 	up_write(&rm->lock);
> 	return ret;
> }
> EXPORT_SYMBOL_GPL(restrictedmem_bind);
> 
> void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
> 			  struct restrictedmem_notifier *notifier)
> {
> 	struct restrictedmem *rm = file->f_mapping->private_data;
> 
> 	down_write(&rm->lock);
> 	xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
> 	synchronize_rcu();
> 	up_write(&rm->lock);
> }
> EXPORT_SYMBOL_GPL(restrictedmem_unbind);

-- 
Alexey

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Thu, Feb 16, 2023, David Hildenbrand wrote:
> On 16.02.23 06:13, Mike Rapoport wrote:
> > Hi,
> > 
> > On Fri, Dec 02, 2022 at 02:13:38PM +0800, Chao Peng wrote:
> > > This patch series implements KVM guest private memory for confidential
> > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > TDX-protected guest memory, machine check can happen which can further
> > > crash the running host system, this is terrible for multi-tenant
> > > configurations. The host accesses include those from KVM userspace like
> > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > via a fd-based approach, but it can never access the guest memory
> > > content.
> > 
> > Sorry for jumping late.
> > 
> > Unless I'm missing something, hibernation will also cause an machine check
> > when there is TDX-protected memory in the system. When the hibernation
> > creates memory snapshot it essentially walks all physical pages and saves
> > their contents, so for TDX memory this will trigger machine check, right?

For hibernation specifically, I think that should be handled elsewhere as hibernation
is simply incompatible with TDX, SNP, pKVM, etc. without paravirtualizing the
guest, as none of those technologies support auto-export a la s390.  I suspect
the right approach is to disallow hibernation if KVM is running any protected guests.

> I recall bringing that up in the past (also memory access due to kdump,
> /prov/kcore) and was told that the main focus for now is preventing
> unprivileged users from crashing the system, that is, not mapping such
> memory into user space (e.g., QEMU). In the long run, we'll want to handle
> such pages also properly in the other events where the kernel might access
> them.

Ya, unless someone strongly objects, the plan is to essentially treat "attacks"
from privileged users as out of to scope for initial support, and then iterate
as needed to fix/enable more features.

FWIW, read accesses, e.g. kdump, should be ok for TDX and SNP as they both play
nice with "bad" reads.  pKVM is a different beast though as I believe any access
to guest private memory will fault.  But my understanding is that this series
would be a big step forward for pKVM, which currently doesn't have any safeguards.

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Chao Peng]

> > int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
> > 		       struct restrictedmem_notifier *notifier, bool exclusive)
> > {
> > 	struct restrictedmem *rm = file->f_mapping->private_data;
> > 	int ret = -EINVAL;
> > 
> > 	down_write(&rm->lock);
> > 
> > 	/* Non-exclusive mappings are not yet implemented. */
> > 	if (!exclusive)
> > 		goto out_unlock;
> > 
> > 	if (!xa_empty(&rm->bindings)) {
> > 		if (exclusive != rm->exclusive)
> > 			goto out_unlock;
> > 
> > 		if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
> > 			goto out_unlock;
> > 	}
> > 
> > 	xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);
> 
> 
> || ld: mm/restrictedmem.o: in function `restrictedmem_bind':
> mm/restrictedmem.c|295| undefined reference to `xa_store_range'

Right, xa_store_range() is only available for XARRAY_MULTI.

> 
> 
> This is missing:
> ===
> diff --git a/mm/Kconfig b/mm/Kconfig
> index f952d0172080..03aca542c0da 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1087,6 +1087,7 @@ config SECRETMEM
>  config RESTRICTEDMEM
>         bool
>         depends on TMPFS
> +       select XARRAY_MULTI
> ===
> 
> Thanks,
> 
> 
> 
> > 	rm->exclusive = exclusive;
> > 	ret = 0;
> > out_unlock:
> > 	up_write(&rm->lock);
> > 	return ret;
> > }
> > EXPORT_SYMBOL_GPL(restrictedmem_bind);
> > 
> > void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
> > 			  struct restrictedmem_notifier *notifier)
> > {
> > 	struct restrictedmem *rm = file->f_mapping->private_data;
> > 
> > 	down_write(&rm->lock);
> > 	xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
> > 	synchronize_rcu();
> > 	up_write(&rm->lock);
> > }
> > EXPORT_SYMBOL_GPL(restrictedmem_unbind);
> 
> -- 
> Alexey

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Ackerley Tng]

Chao Peng <chao.p.peng@linux.intel.com> writes:

> Register/unregister private memslot to fd-based memory backing store
> restrictedmem and implement the callbacks for restrictedmem_notifier:
>    - invalidate_start()/invalidate_end() to zap the existing memory
>      mappings in the KVM page table.
>    - error() to request KVM_REQ_MEMORY_MCE and later exit to userspace
>      with KVM_EXIT_SHUTDOWN.

> Expose KVM_MEM_PRIVATE for memslot and KVM_MEMORY_ATTRIBUTE_PRIVATE for
> KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to userspace but either are
> controlled by kvm_arch_has_private_mem() which should be rewritten by
> architecture code.

Could we perhaps rename KVM_MEM_PRIVATE to KVM_MEM_PROTECTED, to be in
line with KVM_X86_PROTECTED_VM?

I feel that a memslot that has the KVM_MEM_PRIVATE flag need not always
be private; It can sometimes be providing memory that is shared and
also accessible from the host.

KVM_MEMORY_ATTRIBUTE_PRIVATE is fine as-is because this flag is set when
the guest memory is meant to be backed by private memory.

KVM_MEMORY_EXIT_FLAG_PRIVATE is also okay because the flag is used to
indicate when the memory error is caused by a private access (as opposed
to a shared access).

kvm_slot_can_be_private() could perhaps be renamed kvm_is_protected_slot()?


> Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> ---
>   arch/x86/include/asm/kvm_host.h |   1 +
>   arch/x86/kvm/x86.c              |  13 +++
>   include/linux/kvm_host.h        |   3 +
>   virt/kvm/kvm_main.c             | 179 +++++++++++++++++++++++++++++++-
>   4 files changed, 191 insertions(+), 5 deletions(-)

> diff --git a/arch/x86/include/asm/kvm_host.h  
> b/arch/x86/include/asm/kvm_host.h
> index 7772ab37ac89..27ef31133352 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -114,6 +114,7 @@
>   	KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
>   #define KVM_REQ_HV_TLB_FLUSH \
>   	KVM_ARCH_REQ_FLAGS(32, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> +#define KVM_REQ_MEMORY_MCE		KVM_ARCH_REQ(33)

>   #define CR0_RESERVED_BITS                                               \
>   	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5aefcff614d2..c67e22f3e2ee 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6587,6 +6587,13 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned  
> long state)
>   }
>   #endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */

> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +void kvm_arch_memory_mce(struct kvm *kvm)
> +{
> +	kvm_make_all_cpus_request(kvm, KVM_REQ_MEMORY_MCE);
> +}
> +#endif
> +
>   static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp)
>   {
>   	struct kvm_clock_data data = { 0 };
> @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu  
> *vcpu)

>   		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
>   			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> +
> +		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> +			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> +			r = 0;
> +			goto out;
> +		}
>   	}

>   	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 153842bb33df..f032d878e034 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -590,6 +590,7 @@ struct kvm_memory_slot {
>   	struct file *restricted_file;
>   	loff_t restricted_offset;
>   	struct restrictedmem_notifier notifier;
> +	struct kvm *kvm;
>   };

>   static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot  
> *slot)
> @@ -2363,6 +2364,8 @@ static inline int kvm_restricted_mem_get_pfn(struct  
> kvm_memory_slot *slot,
>   	*pfn = page_to_pfn(page);
>   	return ret;
>   }
> +
> +void kvm_arch_memory_mce(struct kvm *kvm);
>   #endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */

>   #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e107afea32f0..ac835fc77273 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -936,6 +936,121 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)

>   #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */

> +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
> +					 pgoff_t start, pgoff_t end,
> +					 gfn_t *gfn_start, gfn_t *gfn_end)
> +{
> +	unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
> +
> +	if (start > base_pgoff)
> +		*gfn_start = slot->base_gfn + start - base_pgoff;
> +	else
> +		*gfn_start = slot->base_gfn;
> +
> +	if (end < base_pgoff + slot->npages)
> +		*gfn_end = slot->base_gfn + end - base_pgoff;
> +	else
> +		*gfn_end = slot->base_gfn + slot->npages;
> +
> +	if (*gfn_start >= *gfn_end)
> +		return false;
> +
> +	return true;
> +}
> +
> +static void kvm_restrictedmem_invalidate_begin(struct  
> restrictedmem_notifier *notifier,
> +					       pgoff_t start, pgoff_t end)
> +{
> +	struct kvm_memory_slot *slot = container_of(notifier,
> +						    struct kvm_memory_slot,
> +						    notifier);
> +	struct kvm *kvm = slot->kvm;
> +	gfn_t gfn_start, gfn_end;
> +	struct kvm_gfn_range gfn_range;
> +	int idx;
> +
> +	if (!restrictedmem_range_is_valid(slot, start, end,
> +					  &gfn_start, &gfn_end))
> +		return;
> +
> +	gfn_range.start = gfn_start;
> +	gfn_range.end = gfn_end;
> +	gfn_range.slot = slot;
> +	gfn_range.pte = __pte(0);
> +	gfn_range.may_block = true;
> +
> +	idx = srcu_read_lock(&kvm->srcu);
> +	KVM_MMU_LOCK(kvm);
> +
> +	kvm_mmu_invalidate_begin(kvm);
> +	kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
> +	if (kvm_unmap_gfn_range(kvm, &gfn_range))
> +		kvm_flush_remote_tlbs(kvm);
> +
> +	KVM_MMU_UNLOCK(kvm);
> +	srcu_read_unlock(&kvm->srcu, idx);
> +}
> +
> +static void kvm_restrictedmem_invalidate_end(struct  
> restrictedmem_notifier *notifier,
> +					     pgoff_t start, pgoff_t end)
> +{
> +	struct kvm_memory_slot *slot = container_of(notifier,
> +						    struct kvm_memory_slot,
> +						    notifier);
> +	struct kvm *kvm = slot->kvm;
> +	gfn_t gfn_start, gfn_end;
> +
> +	if (!restrictedmem_range_is_valid(slot, start, end,
> +					  &gfn_start, &gfn_end))
> +		return;
> +
> +	KVM_MMU_LOCK(kvm);
> +	kvm_mmu_invalidate_end(kvm);
> +	KVM_MMU_UNLOCK(kvm);
> +}
> +
> +static void kvm_restrictedmem_error(struct restrictedmem_notifier  
> *notifier,
> +				    pgoff_t start, pgoff_t end)
> +{
> +	struct kvm_memory_slot *slot = container_of(notifier,
> +						    struct kvm_memory_slot,
> +						    notifier);
> +	kvm_arch_memory_mce(slot->kvm);
> +}
> +
> +static struct restrictedmem_notifier_ops kvm_restrictedmem_notifier_ops  
> = {
> +	.invalidate_start = kvm_restrictedmem_invalidate_begin,
> +	.invalidate_end = kvm_restrictedmem_invalidate_end,
> +	.error = kvm_restrictedmem_error,
> +};
> +
> +static inline void kvm_restrictedmem_register(struct kvm_memory_slot  
> *slot)
> +{
> +	slot->notifier.ops = &kvm_restrictedmem_notifier_ops;
> +	restrictedmem_register_notifier(slot->restricted_file, &slot->notifier);
> +}
> +
> +static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot  
> *slot)
> +{
> +	restrictedmem_unregister_notifier(slot->restricted_file,
> +					  &slot->notifier);
> +}
> +
> +#else /* !CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
> +static inline void kvm_restrictedmem_register(struct kvm_memory_slot  
> *slot)
> +{
> +	WARN_ON_ONCE(1);
> +}
> +
> +static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot  
> *slot)
> +{
> +	WARN_ON_ONCE(1);
> +}
> +
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
>   #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
>   static int kvm_pm_notifier_call(struct notifier_block *bl,
>   				unsigned long state,
> @@ -980,6 +1095,11 @@ static void kvm_destroy_dirty_bitmap(struct  
> kvm_memory_slot *memslot)
>   /* This does not remove the slot from struct kvm_memslots data  
> structures */
>   static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot  
> *slot)
>   {
> +	if (slot->flags & KVM_MEM_PRIVATE) {
> +		kvm_restrictedmem_unregister(slot);
> +		fput(slot->restricted_file);
> +	}
> +
>   	kvm_destroy_dirty_bitmap(slot);

>   	kvm_arch_free_memslot(kvm, slot);
> @@ -1551,10 +1671,14 @@ static void kvm_replace_memslot(struct kvm *kvm,
>   	}
>   }

> -static int check_memory_region_flags(const struct kvm_user_mem_region  
> *mem)
> +static int check_memory_region_flags(struct kvm *kvm,
> +				     const struct kvm_user_mem_region *mem)
>   {
>   	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;

> +	if (kvm_arch_has_private_mem(kvm))
> +		valid_flags |= KVM_MEM_PRIVATE;
> +
>   #ifdef __KVM_HAVE_READONLY_MEM
>   	valid_flags |= KVM_MEM_READONLY;
>   #endif
> @@ -1630,6 +1754,9 @@ static int kvm_prepare_memory_region(struct kvm  
> *kvm,
>   {
>   	int r;

> +	if (change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
> +		kvm_restrictedmem_register(new);
> +
>   	/*
>   	 * If dirty logging is disabled, nullify the bitmap; the old bitmap
>   	 * will be freed on "commit".  If logging is enabled in both old and
> @@ -1658,6 +1785,9 @@ static int kvm_prepare_memory_region(struct kvm  
> *kvm,
>   	if (r && new && new->dirty_bitmap && (!old || !old->dirty_bitmap))
>   		kvm_destroy_dirty_bitmap(new);

> +	if (r && change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
> +		kvm_restrictedmem_unregister(new);
> +
>   	return r;
>   }

> @@ -1963,7 +2093,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>   	int as_id, id;
>   	int r;

> -	r = check_memory_region_flags(mem);
> +	r = check_memory_region_flags(kvm, mem);
>   	if (r)
>   		return r;

> @@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
>   	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
>   			mem->memory_size))
>   		return -EINVAL;
> +	if (mem->flags & KVM_MEM_PRIVATE &&
> +		(mem->restricted_offset & (PAGE_SIZE - 1) ||
> +		 mem->restricted_offset > U64_MAX - mem->memory_size))
> +		return -EINVAL;
>   	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
>   		return -EINVAL;
>   	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
>   		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
>   			return -EINVAL;
>   	} else { /* Modify an existing slot. */
> +		/* Private memslots are immutable, they can only be deleted. */
> +		if (mem->flags & KVM_MEM_PRIVATE)
> +			return -EINVAL;
>   		if ((mem->userspace_addr != old->userspace_addr) ||
>   		    (npages != old->npages) ||
>   		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
>   	new->npages = npages;
>   	new->flags = mem->flags;
>   	new->userspace_addr = mem->userspace_addr;
> +	if (mem->flags & KVM_MEM_PRIVATE) {
> +		new->restricted_file = fget(mem->restricted_fd);
> +		if (!new->restricted_file ||
> +		    !file_is_restrictedmem(new->restricted_file)) {
> +			r = -EINVAL;
> +			goto out;
> +		}
> +		new->restricted_offset = mem->restricted_offset;
> +	}
> +
> +	new->kvm = kvm;

>   	r = kvm_set_memslot(kvm, old, new, change);
>   	if (r)
> -		kfree(new);
> +		goto out;
> +
> +	return 0;
> +
> +out:
> +	if (new->restricted_file)
> +		fput(new->restricted_file);
> +	kfree(new);
>   	return r;
>   }
>   EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> @@ -2351,6 +2506,8 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm  
> *kvm,
>   #ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
>   static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>   {
> +	if (kvm_arch_has_private_mem(kvm))
> +		return KVM_MEMORY_ATTRIBUTE_PRIVATE;
>   	return 0;
>   }

> @@ -4822,16 +4979,28 @@ static long kvm_vm_ioctl(struct file *filp,
>   	}
>   	case KVM_SET_USER_MEMORY_REGION: {
>   		struct kvm_user_mem_region mem;
> -		unsigned long size = sizeof(struct kvm_userspace_memory_region);
> +		unsigned int flags_offset = offsetof(typeof(mem), flags);
> +		unsigned long size;
> +		u32 flags;

>   		kvm_sanity_check_user_mem_region_alias();

> +		memset(&mem, 0, sizeof(mem));
> +
>   		r = -EFAULT;
> +		if (get_user(flags, (u32 __user *)(argp + flags_offset)))
> +			goto out;
> +
> +		if (flags & KVM_MEM_PRIVATE)
> +			size = sizeof(struct kvm_userspace_memory_region_ext);
> +		else
> +			size = sizeof(struct kvm_userspace_memory_region);
> +
>   		if (copy_from_user(&mem, argp, size))
>   			goto out;

>   		r = -EINVAL;
> -		if (mem.flags & KVM_MEM_PRIVATE)
> +		if ((flags ^ mem.flags) & KVM_MEM_PRIVATE)
>   			goto out;

>   		r = kvm_vm_ioctl_set_memory_region(kvm, &mem);

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Sean Christopherson]

Please trim your replies so that readers don't need to scan through a hundred or
so lines of quotes just to confirm there's nothing there.

On Tue, Mar 07, 2023, Ackerley Tng wrote:
> Chao Peng <chao.p.peng@linux.intel.com> writes:
> 
> > Register/unregister private memslot to fd-based memory backing store
> > restrictedmem and implement the callbacks for restrictedmem_notifier:
> >    - invalidate_start()/invalidate_end() to zap the existing memory
> >      mappings in the KVM page table.
> >    - error() to request KVM_REQ_MEMORY_MCE and later exit to userspace
> >      with KVM_EXIT_SHUTDOWN.
> 
> > Expose KVM_MEM_PRIVATE for memslot and KVM_MEMORY_ATTRIBUTE_PRIVATE for
> > KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to userspace but either are
> > controlled by kvm_arch_has_private_mem() which should be rewritten by
> > architecture code.
> 
> Could we perhaps rename KVM_MEM_PRIVATE to KVM_MEM_PROTECTED, to be in
> line with KVM_X86_PROTECTED_VM?
> 
> I feel that a memslot that has the KVM_MEM_PRIVATE flag need not always
> be private; It can sometimes be providing memory that is shared and
> also accessible from the host.
> 
> KVM_MEMORY_ATTRIBUTE_PRIVATE is fine as-is because this flag is set when
> the guest memory is meant to be backed by private memory.
> 
> KVM_MEMORY_EXIT_FLAG_PRIVATE is also okay because the flag is used to
> indicate when the memory error is caused by a private access (as opposed
> to a shared access).
> 
> kvm_slot_can_be_private() could perhaps be renamed kvm_is_protected_slot()?

No to this suggestion.  I agree that KVM_MEM_PRIVATE is a bad name, but
kvm_is_protected_slot() is just as wrong.  The _only_ thing that the flag controls
is whether whether or not the memslot has an fd that is bound to restricted memory.
The memslot itself is not protected in any way, and if the entire memslot is mapped
shared, then the data backed by the memslot isn't protected either.

What about KVM_MEM_CAN_BE_PRIVATE?  KVM_MEM_PRIVATIZABLE is more succinct, but
AFAICT that's a made up word, and IMO is unnecessarily fancy.

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Ackerley Tng]

Chao Peng <chao.p.peng@linux.intel.com> writes:

> On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
>> On Fri, Dec 02, 2022, Chao Peng wrote:
> ...
>> Strongly prefer to use similar logic to existing code that detects wraps:

>> 		mem->restricted_offset + mem->memory_size < mem->restricted_offset

>> This is also where I'd like to add the "gfn is aligned to offset" check,  
>> though
>> my brain is too fried to figure that out right now.

> Used count_trailing_zeros() for this TODO, unsure we have other better
> approach.

> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index afc8c26fa652..fd34c5f7cd2f 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -56,6 +56,7 @@
>   #include <asm/processor.h>
>   #include <asm/ioctl.h>
>   #include <linux/uaccess.h>
> +#include <linux/count_zeros.h>

>   #include "coalesced_mmio.h"
>   #include "async_pf.h"
> @@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct  
> kvm_memslots *slots, int id,
>   	return false;
>   }

> +/*
> + * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
> + */
> +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
> +{
> +	if (!offset)
> +		return true;
> +	if (!gpa)
> +		return false;
> +
> +	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));

Perhaps we could do something like

#define lowest_set_bit(val) (val & -val)

and use

return lowest_set_bit(offset) >= lowest_set_bit(gpa);

Please help me to understand: why must ALIGNMENT(offset) >=
ALIGNMENT(gpa)? Why is it not sufficient to have both gpa and offset be
aligned to PAGE_SIZE?

> +}
> +
>   /*
>    * Allocate some memory and give it an address in the guest physical  
> address
>    * space.
> @@ -2128,7 +2142,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>   	if (mem->flags & KVM_MEM_PRIVATE &&
>   	    (mem->restrictedmem_offset & (PAGE_SIZE - 1) ||
>   	     mem->restrictedmem_offset + mem->memory_size <  
> mem->restrictedmem_offset ||
> -	     0 /* TODO: require gfn be aligned with restricted offset */))
> +	     !kvm_check_rmem_offset_alignment(mem->restrictedmem_offset,
> +					      mem->guest_phys_addr)))
>   		return -EINVAL;
>   	if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_MEM_SLOTS_NUM)
>   		return -EINVAL;

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Wed, Mar 08, 2023 at 12:13:24AM +0000, Ackerley Tng wrote:
> Chao Peng <chao.p.peng@linux.intel.com> writes:
> 
> > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > ...
> > > Strongly prefer to use similar logic to existing code that detects wraps:
> 
> > > 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
> 
> > > This is also where I'd like to add the "gfn is aligned to offset"
> > > check, though
> > > my brain is too fried to figure that out right now.
> 
> > Used count_trailing_zeros() for this TODO, unsure we have other better
> > approach.
> 
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index afc8c26fa652..fd34c5f7cd2f 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -56,6 +56,7 @@
> >   #include <asm/processor.h>
> >   #include <asm/ioctl.h>
> >   #include <linux/uaccess.h>
> > +#include <linux/count_zeros.h>
> 
> >   #include "coalesced_mmio.h"
> >   #include "async_pf.h"
> > @@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct
> > kvm_memslots *slots, int id,
> >   	return false;
> >   }
> 
> > +/*
> > + * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
> > + */
> > +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
> > +{
> > +	if (!offset)
> > +		return true;
> > +	if (!gpa)
> > +		return false;
> > +
> > +	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
> 
> Perhaps we could do something like
> 
> #define lowest_set_bit(val) (val & -val)
> 
> and use
> 
> return lowest_set_bit(offset) >= lowest_set_bit(gpa);

I see kernel already has fls64(), that looks what we need ;)

> 
> Please help me to understand: why must ALIGNMENT(offset) >=
> ALIGNMENT(gpa)? Why is it not sufficient to have both gpa and offset be
> aligned to PAGE_SIZE?

Yes, it's sufficient. Here we just want to be conservative on the uAPI
as Sean explained this at [1]:

  I would rather reject memslot if the gfn has lesser alignment than the
  offset. I'm totally ok with this approach _if_ there's a use case. 
  Until such a use case presents itself, I would rather be conservative
  from a uAPI perspective.

[1] https://lore.kernel.org/all/Y8HldeHBrw+OOZVm@google.com/

Chao
> 
> > +}
> > +
> >   /*
> >    * Allocate some memory and give it an address in the guest physical
> > address
> >    * space.
> > @@ -2128,7 +2142,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >   	if (mem->flags & KVM_MEM_PRIVATE &&
> >   	    (mem->restrictedmem_offset & (PAGE_SIZE - 1) ||
> >   	     mem->restrictedmem_offset + mem->memory_size <
> > mem->restrictedmem_offset ||
> > -	     0 /* TODO: require gfn be aligned with restricted offset */))
> > +	     !kvm_check_rmem_offset_alignment(mem->restrictedmem_offset,
> > +					      mem->guest_phys_addr)))
> >   		return -EINVAL;
> >   	if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_MEM_SLOTS_NUM)
> >   		return -EINVAL;

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Michael Roth]

On Thu, Feb 16, 2023 at 03:21:21PM +0530, Nikunj A. Dadhania wrote:
> 
> > +static struct file *restrictedmem_file_create(struct file *memfd)
> > +{
> > +	struct restrictedmem_data *data;
> > +	struct address_space *mapping;
> > +	struct inode *inode;
> > +	struct file *file;
> > +
> > +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> > +	if (!data)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	data->memfd = memfd;
> > +	mutex_init(&data->lock);
> > +	INIT_LIST_HEAD(&data->notifiers);
> > +
> > +	inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
> > +	if (IS_ERR(inode)) {
> > +		kfree(data);
> > +		return ERR_CAST(inode);
> > +	}
> 
> alloc_anon_inode() uses new_pseudo_inode() to get the inode. As per the comment, new inode 
> is not added to the superblock s_inodes list.

Another issue somewhat related to alloc_anon_inode() is that the shmem code
in some cases assumes the inode struct was allocated via shmem_alloc_inode(),
which allocates a struct shmem_inode_info, which is a superset of struct inode
with additional fields for things like spinlocks.

These additional fields don't get allocated/ininitialized in the case of
restrictedmem, so when restrictedmem_getattr() tries to pass the inode on to
shmem handler, it can cause a crash.

For instance, the following trace was seen when executing 'sudo lsof' while a
process/guest was running with an open memfd FD:

    [24393.121409] general protection fault, probably for non-canonical address 0xfe9fb182fea3f077: 0000 [#1] PREEMPT SMP NOPTI
    [24393.133546] CPU: 2 PID: 590073 Comm: lsof Tainted: G            E      6.1.0-rc4-upm10b-host-snp-v8b+ #4
    [24393.144125] Hardware name: AMD Corporation ETHANOL_X/ETHANOL_X, BIOS RXM1009B 05/14/2022
    [24393.153150] RIP: 0010:native_queued_spin_lock_slowpath+0x3a3/0x3e0
    [24393.160049] Code: f3 90 41 8b 04 24 85 c0 74 ea eb f4 c1 ea 12 83 e0 03 83 ea 01 48 c1 e0 05 48 63 d2 48 05 00 41 04 00 48 03 04 d5 e0 ea 8b 82 <48> 89 18 8b 43 08 85 c0 75 09 f3 90 8b 43 08 85 c0 74 f7 48 8b 13
    [24393.181004] RSP: 0018:ffffc9006b6a3cf8 EFLAGS: 00010086
    [24393.186832] RAX: fe9fb182fea3f077 RBX: ffff889fcc144100 RCX: 0000000000000000
    [24393.194793] RDX: 0000000000003ffe RSI: ffffffff827acde9 RDI: ffffc9006b6a3cdf
    [24393.202751] RBP: ffffc9006b6a3d20 R08: 0000000000000001 R09: 0000000000000000
    [24393.210710] R10: 0000000000000000 R11: 000000000000ffff R12: ffff888179fa50e0
    [24393.218670] R13: ffff889fcc144100 R14: 00000000000c0000 R15: 00000000000c0000
    [24393.226629] FS:  00007f9440f45400(0000) GS:ffff889fcc100000(0000) knlGS:0000000000000000
    [24393.235692] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [24393.242101] CR2: 000055c55a9cf088 CR3: 0008000220e9c003 CR4: 0000000000770ee0
    [24393.250059] PKRU: 55555554
    [24393.253073] Call Trace:
    [24393.255797]  <TASK>
    [24393.258133]  do_raw_spin_lock+0xc4/0xd0
    [24393.262410]  _raw_spin_lock_irq+0x50/0x70
    [24393.266880]  ? shmem_getattr+0x4c/0xf0
    [24393.271060]  shmem_getattr+0x4c/0xf0
    [24393.275044]  restrictedmem_getattr+0x34/0x40
    [24393.279805]  vfs_getattr_nosec+0xbd/0xe0
    [24393.284178]  vfs_getattr+0x37/0x50
    [24393.287971]  vfs_statx+0xa0/0x150
    [24393.291668]  vfs_fstatat+0x59/0x80
    [24393.295462]  __do_sys_newstat+0x35/0x70
    [24393.299739]  __x64_sys_newstat+0x16/0x20
    [24393.304111]  do_syscall_64+0x3b/0x90
    [24393.308098]  entry_SYSCALL_64_after_hwframe+0x63/0xcd

As a workaround we've been doing the following, but it's probably not the
proper fix:

  https://github.com/AMDESE/linux/commit/0378116b5c4e373295c9101727f2cb5112d6b1f4

-Mike

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Isaku Yamahata]

On Wed, Mar 08, 2023 at 03:40:26PM +0800,
Chao Peng <chao.p.peng@linux.intel.com> wrote:

> On Wed, Mar 08, 2023 at 12:13:24AM +0000, Ackerley Tng wrote:
> > Chao Peng <chao.p.peng@linux.intel.com> writes:
> > 
> > > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > ...
> > > > Strongly prefer to use similar logic to existing code that detects wraps:
> > 
> > > > 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
> > 
> > > > This is also where I'd like to add the "gfn is aligned to offset"
> > > > check, though
> > > > my brain is too fried to figure that out right now.
> > 
> > > Used count_trailing_zeros() for this TODO, unsure we have other better
> > > approach.
> > 
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index afc8c26fa652..fd34c5f7cd2f 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -56,6 +56,7 @@
> > >   #include <asm/processor.h>
> > >   #include <asm/ioctl.h>
> > >   #include <linux/uaccess.h>
> > > +#include <linux/count_zeros.h>
> > 
> > >   #include "coalesced_mmio.h"
> > >   #include "async_pf.h"
> > > @@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct
> > > kvm_memslots *slots, int id,
> > >   	return false;
> > >   }
> > 
> > > +/*
> > > + * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
> > > + */
> > > +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
> > > +{
> > > +	if (!offset)
> > > +		return true;
> > > +	if (!gpa)
> > > +		return false;
> > > +
> > > +	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));

This check doesn't work expected. For example, offset = 2GB, gpa=4GB
this check fails.
I come up with the following.

From ec87e25082f0497431b732702fae82c6a05071bf Mon Sep 17 00:00:00 2001
Message-Id: <ec87e25082f0497431b732702fae82c6a05071bf.1679531995.git.isaku.yamahata@intel.com>
From: Isaku Yamahata <isaku.yamahata@intel.com>
Date: Wed, 22 Mar 2023 15:32:56 -0700
Subject: [PATCH] KVM: Relax alignment check for restricted mem

kvm_check_rmem_offset_alignment() only checks based on offset alignment
and GPA alignment.  However, the actual alignment for offset depends
on architecture.  For x86 case, it can be 1G, 2M or 4K.  So even if
GPA is aligned for 1G+, only 1G-alignment is required for offset.

Without this patch, gpa=4G, offset=2G results in failure of memory slot
creation.

Fixes: edc8814b2c77 ("KVM: Require gfn be aligned with restricted offset")
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/include/asm/kvm_host.h | 15 +++++++++++++++
 virt/kvm/kvm_main.c             |  9 ++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 88e11dd3afde..03af44650f24 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -16,6 +16,7 @@
 #include <linux/irq_work.h>
 #include <linux/irq.h>
 #include <linux/workqueue.h>
+#include <linux/count_zeros.h>
 
 #include <linux/kvm.h>
 #include <linux/kvm_para.h>
@@ -143,6 +144,20 @@
 #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
 #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
 
+#define kvm_arch_required_alignment	kvm_arch_required_alignment
+static inline int kvm_arch_required_alignment(u64 gpa)
+{
+	int zeros = count_trailing_zeros(gpa);
+
+	WARN_ON_ONCE(!PAGE_ALIGNED(gpa));
+	if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_1G))
+		return KVM_HPAGE_SHIFT(PG_LEVEL_1G);
+	else if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_2M))
+		return KVM_HPAGE_SHIFT(PG_LEVEL_2M);
+
+	return PAGE_SHIFT;
+}
+
 #define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
 #define KVM_MIN_ALLOC_MMU_PAGES 64UL
 #define KVM_MMU_HASH_SHIFT 12
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c9c4eef457b0..f4ff96171d24 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2113,6 +2113,13 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
 	return false;
 }
 
+#ifndef kvm_arch_required_alignment
+__weak int kvm_arch_required_alignment(u64 gpa)
+{
+	return PAGE_SHIFT
+}
+#endif
+
 /*
  * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
  */
@@ -2123,7 +2130,7 @@ static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
 	if (!gpa)
 		return false;
 
-	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
+	return !!(count_trailing_zeros(offset) >= kvm_arch_required_alignment(gpa));
 }
 
 /*
-- 
2.25.1



-- 
Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Michael Roth]

On Tue, Feb 21, 2023 at 08:11:35PM +0800, Chao Peng wrote:
> > Hi Sean,
> > 
> > We've rebased the SEV+SNP support onto your updated UPM base support
> > tree and things seem to be working okay, but we needed some fixups on
> > top of the base support get things working, along with 1 workaround
> > for an issue that hasn't been root-caused yet:
> > 
> >   https://github.com/mdroth/linux/commits/upmv10b-host-snp-v8-wip
> > 
> >   *stash (upm_base_support): mm: restrictedmem: Kirill's pinning implementation
> >   *workaround (use_base_support): mm: restrictedmem: loosen exclusivity check
> 
> What I'm seeing is Slot#3 gets added first and then deleted. When it's
> gets added, Slot#0 already has the same range bound to restrictedmem so
> trigger the exclusive check. This check is exactly the current code for.

With the following change in QEMU, we no longer trigger this check:

  diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c
  index 20da121374..849b5de469 100644
  --- a/hw/pci-host/q35.c
  +++ b/hw/pci-host/q35.c
  @@ -588,9 +588,9 @@ static void mch_realize(PCIDevice *d, Error **errp)
       memory_region_init_alias(&mch->open_high_smram, OBJECT(mch), "smram-open-high",
                                mch->ram_memory, MCH_HOST_BRIDGE_SMRAM_C_BASE,
                                MCH_HOST_BRIDGE_SMRAM_C_SIZE);
  +    memory_region_set_enabled(&mch->open_high_smram, false);
       memory_region_add_subregion_overlap(mch->system_memory, 0xfeda0000,
                                           &mch->open_high_smram, 1);
  -    memory_region_set_enabled(&mch->open_high_smram, false);

I'm not sure if QEMU is actually doing something wrong here though or if
this check is putting tighter restrictions on userspace than what was
expected before. Will look into it more.

> 
> >   *fixup (upm_base_support): KVM: use inclusive ranges for restrictedmem binding/unbinding
> >   *fixup (upm_base_support): mm: restrictedmem: use inclusive ranges for issuing invalidations
> 
> As many kernel APIs treat 'end' as exclusive, I would rather keep using
> exclusive 'end' for these APIs(restrictedmem_bind/restrictedmem_unbind
> and notifier callbacks) but fix it internally in the restrictedmem. E.g.
> all the places where xarray API needs a 'last'/'max' we use 'end - 1'.
> See below for the change.

Yes I did feel like I was fighting the kernel a bit on that; your
suggestion seems like it would be a better fit.

> 
> >   *fixup (upm_base_support): KVM: fix restrictedmem GFN range calculations
> 
> Subtracting slot->restrictedmem.index for start/end in
> restrictedmem_get_gfn_range() is the correct fix.
> 
> >   *fixup (upm_base_support): KVM: selftests: CoCo compilation fixes
> > 
> > We plan to post an updated RFC for v8 soon, but also wanted to share
> > the staging tree in case you end up looking at the UPM integration aspects
> > before then.
> > 
> > -Mike
> 
> This is the restrictedmem fix to solve 'end' being stored and checked in xarray:

Looks good.

Thanks!

-Mike

> 
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -46,12 +46,12 @@ static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
>          */
>         down_read(&rm->lock);
>  
> -       xa_for_each_range(&rm->bindings, index, notifier, start, end)
> +       xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
>                 notifier->ops->invalidate_start(notifier, start, end);
>  
>         ret = memfd->f_op->fallocate(memfd, mode, offset, len);
>  
> -       xa_for_each_range(&rm->bindings, index, notifier, start, end)
> +       xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
>                 notifier->ops->invalidate_end(notifier, start, end);
>  
>         up_read(&rm->lock);
> @@ -224,7 +224,7 @@ static int restricted_error_remove_page(struct address_space *mapping,
>                 }
>                 spin_unlock(&inode->i_lock);
>  
> -               xa_for_each_range(&rm->bindings, index, notifier, start, end)
> +               xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
>                         notifier->ops->error(notifier, start, end);
>                 break;
>         }
> @@ -301,11 +301,12 @@ int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
>                 if (exclusive != rm->exclusive)
>                         goto out_unlock;
>  
> -               if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
> +               if (exclusive &&
> +                   xa_find(&rm->bindings, &start, end - 1, XA_PRESENT))
>                         goto out_unlock;
>         }
>  
> -       xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);
> +       xa_store_range(&rm->bindings, start, end - 1, notifier, GFP_KERNEL);
>         rm->exclusive = exclusive;
>         ret = 0;
>  out_unlock:
> @@ -320,7 +321,7 @@ void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
>         struct restrictedmem *rm = file->f_mapping->private_data;
>  
>         down_write(&rm->lock);
> -       xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
> +       xa_store_range(&rm->bindings, start, end - 1, NULL, GFP_KERNEL);
>         synchronize_rcu();
>         up_write(&rm->lock);
>  }

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Wed, Mar 22, 2023 at 05:41:31PM -0700, Isaku Yamahata wrote:
> On Wed, Mar 08, 2023 at 03:40:26PM +0800,
> Chao Peng <chao.p.peng@linux.intel.com> wrote:
> 
> > On Wed, Mar 08, 2023 at 12:13:24AM +0000, Ackerley Tng wrote:
> > > Chao Peng <chao.p.peng@linux.intel.com> writes:
> > > 
> > > > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > ...
> > > > > Strongly prefer to use similar logic to existing code that detects wraps:
> > > 
> > > > > 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
> > > 
> > > > > This is also where I'd like to add the "gfn is aligned to offset"
> > > > > check, though
> > > > > my brain is too fried to figure that out right now.
> > > 
> > > > Used count_trailing_zeros() for this TODO, unsure we have other better
> > > > approach.
> > > 
> > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > > index afc8c26fa652..fd34c5f7cd2f 100644
> > > > --- a/virt/kvm/kvm_main.c
> > > > +++ b/virt/kvm/kvm_main.c
> > > > @@ -56,6 +56,7 @@
> > > >   #include <asm/processor.h>
> > > >   #include <asm/ioctl.h>
> > > >   #include <linux/uaccess.h>
> > > > +#include <linux/count_zeros.h>
> > > 
> > > >   #include "coalesced_mmio.h"
> > > >   #include "async_pf.h"
> > > > @@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct
> > > > kvm_memslots *slots, int id,
> > > >   	return false;
> > > >   }
> > > 
> > > > +/*
> > > > + * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
> > > > + */
> > > > +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
> > > > +{
> > > > +	if (!offset)
> > > > +		return true;
> > > > +	if (!gpa)
> > > > +		return false;
> > > > +
> > > > +	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
> 
> This check doesn't work expected. For example, offset = 2GB, gpa=4GB
> this check fails.

This case is expected to fail as Sean initially suggested[*]:
  I would rather reject memslot if the gfn has lesser alignment than
  the offset. I'm totally ok with this approach _if_ there's a use case.
  Until such a use case presents itself, I would rather be conservative
  from a uAPI perspective.

I understand that we put tighter restriction on this but if you see such
restriction is really a big issue for real usage, instead of a
theoretical problem, then we can loosen the check here. But at that time
below code is kind of x86 specific and may need improve.

BTW, in latest code, I replaced count_trailing_zeros() with fls64():
  return !!(fls64(offset) >= fls64(gpa));

[*] https://lore.kernel.org/all/Y8HldeHBrw+OOZVm@google.com/

Chao
> I come up with the following.
> 
> >From ec87e25082f0497431b732702fae82c6a05071bf Mon Sep 17 00:00:00 2001
> Message-Id: <ec87e25082f0497431b732702fae82c6a05071bf.1679531995.git.isaku.yamahata@intel.com>
> From: Isaku Yamahata <isaku.yamahata@intel.com>
> Date: Wed, 22 Mar 2023 15:32:56 -0700
> Subject: [PATCH] KVM: Relax alignment check for restricted mem
> 
> kvm_check_rmem_offset_alignment() only checks based on offset alignment
> and GPA alignment.  However, the actual alignment for offset depends
> on architecture.  For x86 case, it can be 1G, 2M or 4K.  So even if
> GPA is aligned for 1G+, only 1G-alignment is required for offset.
> 
> Without this patch, gpa=4G, offset=2G results in failure of memory slot
> creation.
> 
> Fixes: edc8814b2c77 ("KVM: Require gfn be aligned with restricted offset")
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 15 +++++++++++++++
>  virt/kvm/kvm_main.c             |  9 ++++++++-
>  2 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 88e11dd3afde..03af44650f24 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -16,6 +16,7 @@
>  #include <linux/irq_work.h>
>  #include <linux/irq.h>
>  #include <linux/workqueue.h>
> +#include <linux/count_zeros.h>
>  
>  #include <linux/kvm.h>
>  #include <linux/kvm_para.h>
> @@ -143,6 +144,20 @@
>  #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
>  #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
>  
> +#define kvm_arch_required_alignment	kvm_arch_required_alignment
> +static inline int kvm_arch_required_alignment(u64 gpa)
> +{
> +	int zeros = count_trailing_zeros(gpa);
> +
> +	WARN_ON_ONCE(!PAGE_ALIGNED(gpa));
> +	if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_1G))
> +		return KVM_HPAGE_SHIFT(PG_LEVEL_1G);
> +	else if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_2M))
> +		return KVM_HPAGE_SHIFT(PG_LEVEL_2M);
> +
> +	return PAGE_SHIFT;
> +}
> +
>  #define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
>  #define KVM_MIN_ALLOC_MMU_PAGES 64UL
>  #define KVM_MMU_HASH_SHIFT 12
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index c9c4eef457b0..f4ff96171d24 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2113,6 +2113,13 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
>  	return false;
>  }
>  
> +#ifndef kvm_arch_required_alignment
> +__weak int kvm_arch_required_alignment(u64 gpa)
> +{
> +	return PAGE_SHIFT
> +}
> +#endif
> +
>  /*
>   * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
>   */
> @@ -2123,7 +2130,7 @@ static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
>  	if (!gpa)
>  		return false;
>  
> -	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
> +	return !!(count_trailing_zeros(offset) >= kvm_arch_required_alignment(gpa));
>  }
>  
>  /*
> -- 
> 2.25.1
> 
> 
> 
> -- 
> Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Chao Peng]

On Wed, Mar 22, 2023 at 08:27:37PM -0500, Michael Roth wrote:
> On Tue, Feb 21, 2023 at 08:11:35PM +0800, Chao Peng wrote:
> > > Hi Sean,
> > > 
> > > We've rebased the SEV+SNP support onto your updated UPM base support
> > > tree and things seem to be working okay, but we needed some fixups on
> > > top of the base support get things working, along with 1 workaround
> > > for an issue that hasn't been root-caused yet:
> > > 
> > >   https://github.com/mdroth/linux/commits/upmv10b-host-snp-v8-wip
> > > 
> > >   *stash (upm_base_support): mm: restrictedmem: Kirill's pinning implementation
> > >   *workaround (use_base_support): mm: restrictedmem: loosen exclusivity check
> > 
> > What I'm seeing is Slot#3 gets added first and then deleted. When it's
> > gets added, Slot#0 already has the same range bound to restrictedmem so
> > trigger the exclusive check. This check is exactly the current code for.
> 
> With the following change in QEMU, we no longer trigger this check:
> 
>   diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c
>   index 20da121374..849b5de469 100644
>   --- a/hw/pci-host/q35.c
>   +++ b/hw/pci-host/q35.c
>   @@ -588,9 +588,9 @@ static void mch_realize(PCIDevice *d, Error **errp)
>        memory_region_init_alias(&mch->open_high_smram, OBJECT(mch), "smram-open-high",
>                                 mch->ram_memory, MCH_HOST_BRIDGE_SMRAM_C_BASE,
>                                 MCH_HOST_BRIDGE_SMRAM_C_SIZE);
>   +    memory_region_set_enabled(&mch->open_high_smram, false);
>        memory_region_add_subregion_overlap(mch->system_memory, 0xfeda0000,
>                                            &mch->open_high_smram, 1);
>   -    memory_region_set_enabled(&mch->open_high_smram, false);
> 
> I'm not sure if QEMU is actually doing something wrong here though or if
> this check is putting tighter restrictions on userspace than what was
> expected before. Will look into it more.

I don't think above QEMU change is upstream acceptable. It may break
functionality for 'normal' VMs.

The UPM check does putting tighter restriction, the restriction is that
you can't bind the same fd range to more than one memslot. For SMRAM in
QEMU however, it violates this restriction. The right 'fix' is disabling
SMM in QEMU for UPM usages rather than trying to work around it. There
is more discussion in below link:

  https://lore.kernel.org/all/Y8bOB7VuVIsxoMcn@google.com/

Chao

> 
> > 
> > >   *fixup (upm_base_support): KVM: use inclusive ranges for restrictedmem binding/unbinding
> > >   *fixup (upm_base_support): mm: restrictedmem: use inclusive ranges for issuing invalidations
> > 
> > As many kernel APIs treat 'end' as exclusive, I would rather keep using
> > exclusive 'end' for these APIs(restrictedmem_bind/restrictedmem_unbind
> > and notifier callbacks) but fix it internally in the restrictedmem. E.g.
> > all the places where xarray API needs a 'last'/'max' we use 'end - 1'.
> > See below for the change.
> 
> Yes I did feel like I was fighting the kernel a bit on that; your
> suggestion seems like it would be a better fit.
> 
> > 
> > >   *fixup (upm_base_support): KVM: fix restrictedmem GFN range calculations
> > 
> > Subtracting slot->restrictedmem.index for start/end in
> > restrictedmem_get_gfn_range() is the correct fix.
> > 
> > >   *fixup (upm_base_support): KVM: selftests: CoCo compilation fixes
> > > 
> > > We plan to post an updated RFC for v8 soon, but also wanted to share
> > > the staging tree in case you end up looking at the UPM integration aspects
> > > before then.
> > > 
> > > -Mike
> > 
> > This is the restrictedmem fix to solve 'end' being stored and checked in xarray:
> 
> Looks good.
> 
> Thanks!
> 
> -Mike
> 
> > 
> > --- a/mm/restrictedmem.c
> > +++ b/mm/restrictedmem.c
> > @@ -46,12 +46,12 @@ static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
> >          */
> >         down_read(&rm->lock);
> >  
> > -       xa_for_each_range(&rm->bindings, index, notifier, start, end)
> > +       xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
> >                 notifier->ops->invalidate_start(notifier, start, end);
> >  
> >         ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> >  
> > -       xa_for_each_range(&rm->bindings, index, notifier, start, end)
> > +       xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
> >                 notifier->ops->invalidate_end(notifier, start, end);
> >  
> >         up_read(&rm->lock);
> > @@ -224,7 +224,7 @@ static int restricted_error_remove_page(struct address_space *mapping,
> >                 }
> >                 spin_unlock(&inode->i_lock);
> >  
> > -               xa_for_each_range(&rm->bindings, index, notifier, start, end)
> > +               xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
> >                         notifier->ops->error(notifier, start, end);
> >                 break;
> >         }
> > @@ -301,11 +301,12 @@ int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
> >                 if (exclusive != rm->exclusive)
> >                         goto out_unlock;
> >  
> > -               if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
> > +               if (exclusive &&
> > +                   xa_find(&rm->bindings, &start, end - 1, XA_PRESENT))
> >                         goto out_unlock;
> >         }
> >  
> > -       xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);
> > +       xa_store_range(&rm->bindings, start, end - 1, notifier, GFP_KERNEL);
> >         rm->exclusive = exclusive;
> >         ret = 0;
> >  out_unlock:
> > @@ -320,7 +321,7 @@ void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
> >         struct restrictedmem *rm = file->f_mapping->private_data;
> >  
> >         down_write(&rm->lock);
> > -       xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
> > +       xa_store_range(&rm->bindings, start, end - 1, NULL, GFP_KERNEL);
> >         synchronize_rcu();
> >         up_write(&rm->lock);
> >  }

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Xiaoyao Li]

On 3/24/2023 10:10 AM, Chao Peng wrote:
> On Wed, Mar 22, 2023 at 05:41:31PM -0700, Isaku Yamahata wrote:
>> On Wed, Mar 08, 2023 at 03:40:26PM +0800,
>> Chao Peng <chao.p.peng@linux.intel.com> wrote:
>>
>>> On Wed, Mar 08, 2023 at 12:13:24AM +0000, Ackerley Tng wrote:
>>>> Chao Peng <chao.p.peng@linux.intel.com> writes:
>>>>
>>>>> On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
>>>>>> On Fri, Dec 02, 2022, Chao Peng wrote:
>>>>> ...
>>>>>> Strongly prefer to use similar logic to existing code that detects wraps:
>>>>
>>>>>> 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
>>>>
>>>>>> This is also where I'd like to add the "gfn is aligned to offset"
>>>>>> check, though
>>>>>> my brain is too fried to figure that out right now.
>>>>
>>>>> Used count_trailing_zeros() for this TODO, unsure we have other better
>>>>> approach.
>>>>
>>>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>>>>> index afc8c26fa652..fd34c5f7cd2f 100644
>>>>> --- a/virt/kvm/kvm_main.c
>>>>> +++ b/virt/kvm/kvm_main.c
>>>>> @@ -56,6 +56,7 @@
>>>>>    #include <asm/processor.h>
>>>>>    #include <asm/ioctl.h>
>>>>>    #include <linux/uaccess.h>
>>>>> +#include <linux/count_zeros.h>
>>>>
>>>>>    #include "coalesced_mmio.h"
>>>>>    #include "async_pf.h"
>>>>> @@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct
>>>>> kvm_memslots *slots, int id,
>>>>>    	return false;
>>>>>    }
>>>>
>>>>> +/*
>>>>> + * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
>>>>> + */
>>>>> +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
>>>>> +{
>>>>> +	if (!offset)
>>>>> +		return true;
>>>>> +	if (!gpa)
>>>>> +		return false;
>>>>> +
>>>>> +	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
>>
>> This check doesn't work expected. For example, offset = 2GB, gpa=4GB
>> this check fails.
> 
> This case is expected to fail as Sean initially suggested[*]:
>    I would rather reject memslot if the gfn has lesser alignment than
>    the offset. I'm totally ok with this approach _if_ there's a use case.
>    Until such a use case presents itself, I would rather be conservative
>    from a uAPI perspective.
> 
> I understand that we put tighter restriction on this but if you see such
> restriction is really a big issue for real usage, instead of a
> theoretical problem, then we can loosen the check here. But at that time
> below code is kind of x86 specific and may need improve.
> 
> BTW, in latest code, I replaced count_trailing_zeros() with fls64():
>    return !!(fls64(offset) >= fls64(gpa));

wouldn't it be !!(ffs64(offset) <= ffs64(gpa)) ?

> [*] https://lore.kernel.org/all/Y8HldeHBrw+OOZVm@google.com/
> 
> Chao
>> I come up with the following.
>>
>> >From ec87e25082f0497431b732702fae82c6a05071bf Mon Sep 17 00:00:00 2001
>> Message-Id: <ec87e25082f0497431b732702fae82c6a05071bf.1679531995.git.isaku.yamahata@intel.com>
>> From: Isaku Yamahata <isaku.yamahata@intel.com>
>> Date: Wed, 22 Mar 2023 15:32:56 -0700
>> Subject: [PATCH] KVM: Relax alignment check for restricted mem
>>
>> kvm_check_rmem_offset_alignment() only checks based on offset alignment
>> and GPA alignment.  However, the actual alignment for offset depends
>> on architecture.  For x86 case, it can be 1G, 2M or 4K.  So even if
>> GPA is aligned for 1G+, only 1G-alignment is required for offset.
>>
>> Without this patch, gpa=4G, offset=2G results in failure of memory slot
>> creation.
>>
>> Fixes: edc8814b2c77 ("KVM: Require gfn be aligned with restricted offset")
>> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
>> ---
>>   arch/x86/include/asm/kvm_host.h | 15 +++++++++++++++
>>   virt/kvm/kvm_main.c             |  9 ++++++++-
>>   2 files changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 88e11dd3afde..03af44650f24 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -16,6 +16,7 @@
>>   #include <linux/irq_work.h>
>>   #include <linux/irq.h>
>>   #include <linux/workqueue.h>
>> +#include <linux/count_zeros.h>
>>   
>>   #include <linux/kvm.h>
>>   #include <linux/kvm_para.h>
>> @@ -143,6 +144,20 @@
>>   #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
>>   #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
>>   
>> +#define kvm_arch_required_alignment	kvm_arch_required_alignment
>> +static inline int kvm_arch_required_alignment(u64 gpa)
>> +{
>> +	int zeros = count_trailing_zeros(gpa);
>> +
>> +	WARN_ON_ONCE(!PAGE_ALIGNED(gpa));
>> +	if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_1G))
>> +		return KVM_HPAGE_SHIFT(PG_LEVEL_1G);
>> +	else if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_2M))
>> +		return KVM_HPAGE_SHIFT(PG_LEVEL_2M);
>> +
>> +	return PAGE_SHIFT;
>> +}
>> +
>>   #define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
>>   #define KVM_MIN_ALLOC_MMU_PAGES 64UL
>>   #define KVM_MMU_HASH_SHIFT 12
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index c9c4eef457b0..f4ff96171d24 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -2113,6 +2113,13 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
>>   	return false;
>>   }
>>   
>> +#ifndef kvm_arch_required_alignment
>> +__weak int kvm_arch_required_alignment(u64 gpa)
>> +{
>> +	return PAGE_SHIFT
>> +}
>> +#endif
>> +
>>   /*
>>    * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
>>    */
>> @@ -2123,7 +2130,7 @@ static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
>>   	if (!gpa)
>>   		return false;
>>   
>> -	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
>> +	return !!(count_trailing_zeros(offset) >= kvm_arch_required_alignment(gpa));
>>   }
>>   
>>   /*
>> -- 
>> 2.25.1
>>
>>
>>
>> -- 
>> Isaku Yamahata <isaku.yamahata@gmail.com>

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Chao Peng]

On Fri, Mar 24, 2023 at 10:29:25AM +0800, Xiaoyao Li wrote:
> On 3/24/2023 10:10 AM, Chao Peng wrote:
> > On Wed, Mar 22, 2023 at 05:41:31PM -0700, Isaku Yamahata wrote:
> > > On Wed, Mar 08, 2023 at 03:40:26PM +0800,
> > > Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > > 
> > > > On Wed, Mar 08, 2023 at 12:13:24AM +0000, Ackerley Tng wrote:
> > > > > Chao Peng <chao.p.peng@linux.intel.com> writes:
> > > > > 
> > > > > > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> > > > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > > ...
> > > > > > > Strongly prefer to use similar logic to existing code that detects wraps:
> > > > > 
> > > > > > > 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
> > > > > 
> > > > > > > This is also where I'd like to add the "gfn is aligned to offset"
> > > > > > > check, though
> > > > > > > my brain is too fried to figure that out right now.
> > > > > 
> > > > > > Used count_trailing_zeros() for this TODO, unsure we have other better
> > > > > > approach.
> > > > > 
> > > > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > > > > index afc8c26fa652..fd34c5f7cd2f 100644
> > > > > > --- a/virt/kvm/kvm_main.c
> > > > > > +++ b/virt/kvm/kvm_main.c
> > > > > > @@ -56,6 +56,7 @@
> > > > > >    #include <asm/processor.h>
> > > > > >    #include <asm/ioctl.h>
> > > > > >    #include <linux/uaccess.h>
> > > > > > +#include <linux/count_zeros.h>
> > > > > 
> > > > > >    #include "coalesced_mmio.h"
> > > > > >    #include "async_pf.h"
> > > > > > @@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct
> > > > > > kvm_memslots *slots, int id,
> > > > > >    	return false;
> > > > > >    }
> > > > > 
> > > > > > +/*
> > > > > > + * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
> > > > > > + */
> > > > > > +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
> > > > > > +{
> > > > > > +	if (!offset)
> > > > > > +		return true;
> > > > > > +	if (!gpa)
> > > > > > +		return false;
> > > > > > +
> > > > > > +	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
> > > 
> > > This check doesn't work expected. For example, offset = 2GB, gpa=4GB
> > > this check fails.
> > 
> > This case is expected to fail as Sean initially suggested[*]:
> >    I would rather reject memslot if the gfn has lesser alignment than
> >    the offset. I'm totally ok with this approach _if_ there's a use case.
> >    Until such a use case presents itself, I would rather be conservative
> >    from a uAPI perspective.
> > 
> > I understand that we put tighter restriction on this but if you see such
> > restriction is really a big issue for real usage, instead of a
> > theoretical problem, then we can loosen the check here. But at that time
> > below code is kind of x86 specific and may need improve.
> > 
> > BTW, in latest code, I replaced count_trailing_zeros() with fls64():
> >    return !!(fls64(offset) >= fls64(gpa));
> 
> wouldn't it be !!(ffs64(offset) <= ffs64(gpa)) ?

As the function document explains, here we want to return true when
ALIGNMENT(offset) >= ALIGNMENT(gpa), so '>=' is what we need.

It's worthy clarifying that in Sean's original suggestion he actually
mentioned the opposite. He said 'reject memslot if the gfn has lesser
alignment than the offset', but I wonder this is his purpose, since
if ALIGNMENT(offset) < ALIGNMENT(gpa), we wouldn't be possible to map
the page as largepage. Consider we have below config:

  gpa=2M, offset=1M

In this case KVM tries to map gpa at 2M as 2M hugepage but the physical
page at the offset(1M) in private_fd cannot provide the 2M page due to
misalignment.

But as we discussed in the off-list thread, here we do find a real use
case indicating this check is too strict. i.e. QEMU immediately fails
when launch a guest > 2G memory. For this case QEMU splits guest memory
space into two slots:

  Slot#1(ram_below_4G): gpa=0x0, offset=0x0, size=2G
  Slot#2(ram_above_4G): gpa=4G,  offset=2G,  size=totalsize-2G

This strict alignment check fails for slot#2 because offset(2G) has less
alignment than gpa(4G). To allow this, one solution can revert to my
previous change in kvm_alloc_memslot_metadata() to disallow hugepage
only when the offset/gpa are not aligned to related page size.

Sean, How do you think?

Chao
> 
> > [*] https://lore.kernel.org/all/Y8HldeHBrw+OOZVm@google.com/
> > 
> > Chao
> > > I come up with the following.
> > > 
> > > >From ec87e25082f0497431b732702fae82c6a05071bf Mon Sep 17 00:00:00 2001
> > > Message-Id: <ec87e25082f0497431b732702fae82c6a05071bf.1679531995.git.isaku.yamahata@intel.com>
> > > From: Isaku Yamahata <isaku.yamahata@intel.com>
> > > Date: Wed, 22 Mar 2023 15:32:56 -0700
> > > Subject: [PATCH] KVM: Relax alignment check for restricted mem
> > > 
> > > kvm_check_rmem_offset_alignment() only checks based on offset alignment
> > > and GPA alignment.  However, the actual alignment for offset depends
> > > on architecture.  For x86 case, it can be 1G, 2M or 4K.  So even if
> > > GPA is aligned for 1G+, only 1G-alignment is required for offset.
> > > 
> > > Without this patch, gpa=4G, offset=2G results in failure of memory slot
> > > creation.
> > > 
> > > Fixes: edc8814b2c77 ("KVM: Require gfn be aligned with restricted offset")
> > > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > > ---
> > >   arch/x86/include/asm/kvm_host.h | 15 +++++++++++++++
> > >   virt/kvm/kvm_main.c             |  9 ++++++++-
> > >   2 files changed, 23 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > > index 88e11dd3afde..03af44650f24 100644
> > > --- a/arch/x86/include/asm/kvm_host.h
> > > +++ b/arch/x86/include/asm/kvm_host.h
> > > @@ -16,6 +16,7 @@
> > >   #include <linux/irq_work.h>
> > >   #include <linux/irq.h>
> > >   #include <linux/workqueue.h>
> > > +#include <linux/count_zeros.h>
> > >   #include <linux/kvm.h>
> > >   #include <linux/kvm_para.h>
> > > @@ -143,6 +144,20 @@
> > >   #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
> > >   #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
> > > +#define kvm_arch_required_alignment	kvm_arch_required_alignment
> > > +static inline int kvm_arch_required_alignment(u64 gpa)
> > > +{
> > > +	int zeros = count_trailing_zeros(gpa);
> > > +
> > > +	WARN_ON_ONCE(!PAGE_ALIGNED(gpa));
> > > +	if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_1G))
> > > +		return KVM_HPAGE_SHIFT(PG_LEVEL_1G);
> > > +	else if (zeros >= KVM_HPAGE_SHIFT(PG_LEVEL_2M))
> > > +		return KVM_HPAGE_SHIFT(PG_LEVEL_2M);
> > > +
> > > +	return PAGE_SHIFT;
> > > +}
> > > +
> > >   #define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
> > >   #define KVM_MIN_ALLOC_MMU_PAGES 64UL
> > >   #define KVM_MMU_HASH_SHIFT 12
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index c9c4eef457b0..f4ff96171d24 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -2113,6 +2113,13 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
> > >   	return false;
> > >   }
> > > +#ifndef kvm_arch_required_alignment
> > > +__weak int kvm_arch_required_alignment(u64 gpa)
> > > +{
> > > +	return PAGE_SHIFT
> > > +}
> > > +#endif
> > > +
> > >   /*
> > >    * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
> > >    */
> > > @@ -2123,7 +2130,7 @@ static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
> > >   	if (!gpa)
> > >   		return false;
> > > -	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
> > > +	return !!(count_trailing_zeros(offset) >= kvm_arch_required_alignment(gpa));
> > >   }
> > >   /*
> > > -- 
> > > 2.25.1
> > > 
> > > 
> > > 
> > > -- 
> > > Isaku Yamahata <isaku.yamahata@gmail.com>

[RFC PATCH v3 0/2] Providing mount in memfd_restricted() syscall

[Ackerley Tng]

Hello,

This patchset builds upon the memfd_restricted() system call that was
discussed in the ‘KVM: mm: fd-based approach for supporting KVM’ patch
series, at
https://lore.kernel.org/lkml/20221202061347.1070246-1-chao.p.peng@linux.intel.com/T/

The tree can be found at:
https://github.com/googleprodkernel/linux-cc/tree/restrictedmem-provide-mount-fd-rfc-v3

In this patchset, a modification to the memfd_restricted() syscall is
proposed, which allows userspace to provide a mount, on which the
restrictedmem file will be created and returned from the
memfd_restricted().

Allowing userspace to provide a mount allows userspace to control
various memory binding policies via tmpfs mount options, such as
Transparent HugePage memory allocation policy through
‘huge=always/never’ and NUMA memory allocation policy through
‘mpol=local/bind:*’.

Changes since RFCv2:
+ Tightened semantics to accept only fds of the root of a tmpfs mount,
  as Christian suggested
+ Added permissions check on the inode represented by the fd to guard
  against creation of restrictedmem files on read-only tmpfs
  filesystems or mounts
+ Renamed RMFD_TMPFILE to RMFD_USERMNT to better represent providing a
  userspace mount to create a restrictedmem file on
+ Updated selftests for tighter semantics and added selftests to check
  for permissions

Changes since RFCv1:
+ Use fd to represent mount instead of path string, as Kirill
  suggested. I believe using fds makes this syscall interface more
  aligned with the other syscalls like fsopen(), fsconfig(), and
  fsmount() in terms of using and passing around fds
+ Remove unused variable char *orig_shmem_enabled from selftests

Dependencies:
+ Sean’s iteration of the ‘KVM: mm: fd-based approach for supporting
  KVM’ patch series at
  https://github.com/sean-jc/linux/tree/x86/upm_base_support
+ Proposed fixes for these issues mentioned on the mailing list:
    + https://lore.kernel.org/lkml/diqzzga0fv96.fsf@ackerleytng-cloudtop-sg.c.googlers.com/

Links to earlier patch series:
+ RFC v2: https://lore.kernel.org/lkml/cover.1679428901.git.ackerleytng@google.com/T/
+ RFC v1: https://lore.kernel.org/lkml/cover.1676507663.git.ackerleytng@google.com/T/

---

Ackerley Tng (2):
  mm: restrictedmem: Allow userspace to specify mount for
    memfd_restricted
  selftests: restrictedmem: Check hugepage-ness of shmem file backing
    restrictedmem fd

 include/linux/syscalls.h                      |   2 +-
 include/uapi/linux/restrictedmem.h            |   8 +
 mm/restrictedmem.c                            |  74 ++-
 tools/testing/selftests/Makefile              |   1 +
 .../selftests/restrictedmem/.gitignore        |   3 +
 .../testing/selftests/restrictedmem/Makefile  |  15 +
 .../testing/selftests/restrictedmem/common.c  |   9 +
 .../testing/selftests/restrictedmem/common.h  |   8 +
 .../restrictedmem_hugepage_test.c             | 486 ++++++++++++++++++
 9 files changed, 599 insertions(+), 7 deletions(-)
 create mode 100644 include/uapi/linux/restrictedmem.h
 create mode 100644 tools/testing/selftests/restrictedmem/.gitignore
 create mode 100644 tools/testing/selftests/restrictedmem/Makefile
 create mode 100644 tools/testing/selftests/restrictedmem/common.c
 create mode 100644 tools/testing/selftests/restrictedmem/common.h
 create mode 100644 tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c

--
2.40.0.348.gf938b09366-goog

[RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Ackerley Tng]

By default, the backing shmem file for a restrictedmem fd is created
on shmem's kernel space mount.

With this patch, an optional tmpfs mount can be specified via an fd,
which will be used as the mountpoint for backing the shmem file
associated with a restrictedmem fd.

This will help restrictedmem fds inherit the properties of the
provided tmpfs mounts, for example, hugepage allocation hints, NUMA
binding hints, etc.

Permissions for the fd passed to memfd_restricted() is modeled after
the openat() syscall, since both of these allow creation of a file
upon a mount/directory.

Permission to reference the mount the fd represents is checked upon fd
creation by other syscalls (e.g. fsmount(), open(), or open_tree(),
etc) and any process that can present memfd_restricted() with a valid
fd is expected to have obtained permission to use the mount
represented by the fd. This behavior is intended to parallel that of
the openat() syscall.

memfd_restricted() will check that the tmpfs superblock is
writable, and that the mount is also writable, before attempting to
create a restrictedmem file on the mount.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 include/linux/syscalls.h           |  2 +-
 include/uapi/linux/restrictedmem.h |  8 ++++
 mm/restrictedmem.c                 | 74 +++++++++++++++++++++++++++---
 3 files changed, 77 insertions(+), 7 deletions(-)
 create mode 100644 include/uapi/linux/restrictedmem.h

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f9e9e0c820c5..a23c4c385cd3 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1056,7 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
 asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
 					    unsigned long home_node,
 					    unsigned long flags);
-asmlinkage long sys_memfd_restricted(unsigned int flags);
+asmlinkage long sys_memfd_restricted(unsigned int flags, int mount_fd);

 /*
  * Architecture-specific system calls
diff --git a/include/uapi/linux/restrictedmem.h b/include/uapi/linux/restrictedmem.h
new file mode 100644
index 000000000000..22d6f2285f6d
--- /dev/null
+++ b/include/uapi/linux/restrictedmem.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_RESTRICTEDMEM_H
+#define _UAPI_LINUX_RESTRICTEDMEM_H
+
+/* flags for memfd_restricted */
+#define RMFD_USERMNT		0x0001U
+
+#endif /* _UAPI_LINUX_RESTRICTEDMEM_H */
diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
index c5d869d8c2d8..f7b62364a31a 100644
--- a/mm/restrictedmem.c
+++ b/mm/restrictedmem.c
@@ -1,11 +1,12 @@
 // SPDX-License-Identifier: GPL-2.0
-#include "linux/sbitmap.h"
+#include <linux/namei.h>
 #include <linux/pagemap.h>
 #include <linux/pseudo_fs.h>
 #include <linux/shmem_fs.h>
 #include <linux/syscalls.h>
 #include <uapi/linux/falloc.h>
 #include <uapi/linux/magic.h>
+#include <uapi/linux/restrictedmem.h>
 #include <linux/restrictedmem.h>

 struct restrictedmem {
@@ -189,19 +190,20 @@ static struct file *restrictedmem_file_create(struct file *memfd)
 	return file;
 }

-SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
+static int restrictedmem_create(struct vfsmount *mount)
 {
 	struct file *file, *restricted_file;
 	int fd, err;

-	if (flags)
-		return -EINVAL;
-
 	fd = get_unused_fd_flags(0);
 	if (fd < 0)
 		return fd;

-	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
+	if (mount)
+		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0, VM_NORESERVE);
+	else
+		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
+
 	if (IS_ERR(file)) {
 		err = PTR_ERR(file);
 		goto err_fd;
@@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
 	return err;
 }

+static bool is_shmem_mount(struct vfsmount *mnt)
+{
+	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;
+}
+
+static bool is_mount_root(struct file *file)
+{
+	return file->f_path.dentry == file->f_path.mnt->mnt_root;
+}
+
+static int restrictedmem_create_on_user_mount(int mount_fd)
+{
+	int ret;
+	struct fd f;
+	struct vfsmount *mnt;
+
+	f = fdget_raw(mount_fd);
+	if (!f.file)
+		return -EBADF;
+
+	ret = -EINVAL;
+	if (!is_mount_root(f.file))
+		goto out;
+
+	mnt = f.file->f_path.mnt;
+	if (!is_shmem_mount(mnt))
+		goto out;
+
+	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);
+	if (ret)
+		goto out;
+
+	ret = mnt_want_write(mnt);
+	if (unlikely(ret))
+		goto out;
+
+	ret = restrictedmem_create(mnt);
+
+	mnt_drop_write(mnt);
+out:
+	fdput(f);
+
+	return ret;
+}
+
+SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
+{
+	if (flags & ~RMFD_USERMNT)
+		return -EINVAL;
+
+	if (flags == RMFD_USERMNT) {
+		if (mount_fd < 0)
+			return -EINVAL;
+
+		return restrictedmem_create_on_user_mount(mount_fd);
+	} else {
+		return restrictedmem_create(NULL);
+	}
+}
+
 int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
 		       struct restrictedmem_notifier *notifier, bool exclusive)
 {
--
2.40.0.348.gf938b09366-goog

[RFC PATCH v3 2/2] selftests: restrictedmem: Check hugepage-ness of shmem file backing restrictedmem fd

[Ackerley Tng]

For memfd_restricted() calls without a userspace mount, the backing
file should be the shmem mount in the kernel, and the size of backing
pages should be as defined by system-wide shmem configuration.

If a userspace mount is provided, the size of backing pages should be
as defined in the mount.

Also includes negative tests for invalid inputs, including fds
representing read-only superblocks/mounts.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 tools/testing/selftests/Makefile              |   1 +
 .../selftests/restrictedmem/.gitignore        |   3 +
 .../testing/selftests/restrictedmem/Makefile  |  15 +
 .../testing/selftests/restrictedmem/common.c  |   9 +
 .../testing/selftests/restrictedmem/common.h  |   8 +
 .../restrictedmem_hugepage_test.c             | 486 ++++++++++++++++++
 6 files changed, 522 insertions(+)
 create mode 100644 tools/testing/selftests/restrictedmem/.gitignore
 create mode 100644 tools/testing/selftests/restrictedmem/Makefile
 create mode 100644 tools/testing/selftests/restrictedmem/common.c
 create mode 100644 tools/testing/selftests/restrictedmem/common.h
 create mode 100644 tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index f07aef7c592c..44078eeefb79 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -60,6 +60,7 @@ TARGETS += pstore
 TARGETS += ptrace
 TARGETS += openat2
 TARGETS += resctrl
+TARGETS += restrictedmem
 TARGETS += rlimits
 TARGETS += rseq
 TARGETS += rtc
diff --git a/tools/testing/selftests/restrictedmem/.gitignore b/tools/testing/selftests/restrictedmem/.gitignore
new file mode 100644
index 000000000000..2581bcc8ff29
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+restrictedmem_hugepage_test
diff --git a/tools/testing/selftests/restrictedmem/Makefile b/tools/testing/selftests/restrictedmem/Makefile
new file mode 100644
index 000000000000..8e5378d20226
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/Makefile
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS = $(KHDR_INCLUDES)
+CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -std=gnu99
+
+TEST_GEN_PROGS += restrictedmem_hugepage_test
+
+include ../lib.mk
+
+EXTRA_CLEAN = $(OUTPUT)/common.o
+
+$(OUTPUT)/common.o: common.c
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c -ffreestanding $< -o $@
+
+$(TEST_GEN_PROGS): $(OUTPUT)/common.o
diff --git a/tools/testing/selftests/restrictedmem/common.c b/tools/testing/selftests/restrictedmem/common.c
new file mode 100644
index 000000000000..03dac843404f
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/common.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <sys/syscall.h>
+#include <unistd.h>
+
+int memfd_restricted(unsigned int flags, int mount_fd)
+{
+	return syscall(__NR_memfd_restricted, flags, mount_fd);
+}
diff --git a/tools/testing/selftests/restrictedmem/common.h b/tools/testing/selftests/restrictedmem/common.h
new file mode 100644
index 000000000000..06284ed86baf
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/common.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef SELFTESTS_RESTRICTEDMEM_COMMON_H
+#define SELFTESTS_RESTRICTEDMEM_COMMON_H
+
+int memfd_restricted(unsigned int flags, int mount_fd);
+
+#endif  // SELFTESTS_RESTRICTEDMEM_COMMON_H
diff --git a/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
new file mode 100644
index 000000000000..9ed319b83cb8
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
@@ -0,0 +1,486 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#define _GNU_SOURCE /* for O_PATH */
+#define _POSIX_C_SOURCE /* for PATH_MAX */
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "linux/restrictedmem.h"
+
+#include "common.h"
+#include "../kselftest_harness.h"
+
+/*
+ * Expect policy to be one of always, within_size, advise, never,
+ * deny, force
+ */
+#define POLICY_BUF_SIZE 12
+
+static int get_hpage_pmd_size(void)
+{
+	FILE *fp;
+	char buf[100];
+	char *ret;
+	int size;
+
+	fp = fopen("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", "r");
+	if (!fp)
+		return -1;
+
+	ret = fgets(buf, 100, fp);
+	if (ret != buf) {
+		size = -1;
+		goto out;
+	}
+
+	if (sscanf(buf, "%d\n", &size) != 1)
+		size = -1;
+
+out:
+	fclose(fp);
+
+	return size;
+}
+
+static bool is_valid_shmem_thp_policy(char *policy)
+{
+	if (strcmp(policy, "always") == 0)
+		return true;
+	if (strcmp(policy, "within_size") == 0)
+		return true;
+	if (strcmp(policy, "advise") == 0)
+		return true;
+	if (strcmp(policy, "never") == 0)
+		return true;
+	if (strcmp(policy, "deny") == 0)
+		return true;
+	if (strcmp(policy, "force") == 0)
+		return true;
+
+	return false;
+}
+
+static int get_shmem_thp_policy(char *policy)
+{
+	FILE *fp;
+	char buf[100];
+	char *left = NULL;
+	char *right = NULL;
+	int ret = -1;
+
+	fp = fopen("/sys/kernel/mm/transparent_hugepage/shmem_enabled", "r");
+	if (!fp)
+		return -1;
+
+	if (fgets(buf, 100, fp) != buf)
+		goto out;
+
+	/*
+	 * Expect shmem_enabled to be of format like "always within_size advise
+	 * [never] deny force"
+	 */
+	left = memchr(buf, '[', 100);
+	if (!left)
+		goto out;
+
+	right = memchr(buf, ']', 100);
+	if (!right)
+		goto out;
+
+	memcpy(policy, left + 1, right - left - 1);
+
+	ret = !is_valid_shmem_thp_policy(policy);
+
+out:
+	fclose(fp);
+	return ret;
+}
+
+static int write_string_to_file(const char *path, const char *string)
+{
+	FILE *fp;
+	size_t len = strlen(string);
+	int ret = -1;
+
+	fp = fopen(path, "w");
+	if (!fp)
+		return ret;
+
+	if (fwrite(string, 1, len, fp) != len)
+		goto out;
+
+	ret = 0;
+
+out:
+	fclose(fp);
+	return ret;
+}
+
+static int set_shmem_thp_policy(char *policy)
+{
+	int ret = -1;
+	/* +1 for newline */
+	char to_write[POLICY_BUF_SIZE + 1] = { 0 };
+
+	if (!is_valid_shmem_thp_policy(policy))
+		return ret;
+
+	ret = snprintf(to_write, POLICY_BUF_SIZE + 1, "%s\n", policy);
+	if (ret != strlen(policy) + 1)
+		return -1;
+
+	ret = write_string_to_file(
+		"/sys/kernel/mm/transparent_hugepage/shmem_enabled", to_write);
+
+	return ret;
+}
+
+FIXTURE(reset_shmem_enabled)
+{
+	char shmem_enabled[POLICY_BUF_SIZE];
+};
+
+FIXTURE_SETUP(reset_shmem_enabled)
+{
+	memset(self->shmem_enabled, 0, POLICY_BUF_SIZE);
+	ASSERT_EQ(get_shmem_thp_policy(self->shmem_enabled), 0);
+}
+
+FIXTURE_TEARDOWN(reset_shmem_enabled)
+{
+	ASSERT_EQ(set_shmem_thp_policy(self->shmem_enabled), 0);
+}
+
+TEST_F(reset_shmem_enabled, restrictedmem_fstat_shmem_enabled_never)
+{
+	int fd = -1;
+	struct stat stat;
+
+	ASSERT_EQ(set_shmem_thp_policy("never"), 0);
+
+	fd = memfd_restricted(0, -1);
+	ASSERT_GT(fd, 0);
+
+	ASSERT_EQ(fstat(fd, &stat), 0);
+
+	/*
+	 * st_blksize is set based on the superblock's s_blocksize_bits. For
+	 * shmem, this is set to PAGE_SHIFT
+	 */
+	ASSERT_EQ(stat.st_blksize, getpagesize());
+
+	close(fd);
+}
+
+TEST_F(reset_shmem_enabled, restrictedmem_fstat_shmem_enabled_always)
+{
+	int fd = -1;
+	struct stat stat;
+
+	ASSERT_EQ(set_shmem_thp_policy("always"), 0);
+
+	fd = memfd_restricted(0, -1);
+	ASSERT_GT(fd, 0);
+
+	ASSERT_EQ(fstat(fd, &stat), 0);
+
+	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
+
+	close(fd);
+}
+
+TEST(restrictedmem_tmpfile_invalid_fd)
+{
+	int fd = memfd_restricted(RMFD_USERMNT, -2);
+
+	ASSERT_EQ(fd, -1);
+	ASSERT_EQ(errno, EINVAL);
+}
+
+TEST(restrictedmem_tmpfile_fd_not_a_mount)
+{
+	int fd = memfd_restricted(RMFD_USERMNT, STDOUT_FILENO);
+
+	ASSERT_EQ(fd, -1);
+	ASSERT_EQ(errno, EINVAL);
+}
+
+TEST(restrictedmem_tmpfile_not_tmpfs_mount)
+{
+	int fd = -1;
+	int mfd = -1;
+
+	mfd = open("/proc", O_PATH);
+	ASSERT_NE(mfd, -1);
+
+	fd = memfd_restricted(RMFD_USERMNT, mfd);
+
+	ASSERT_EQ(fd, -1);
+	ASSERT_EQ(errno, EINVAL);
+}
+
+FIXTURE(tmpfs_hugepage_sfd)
+{
+	int sfd;
+};
+
+FIXTURE_SETUP(tmpfs_hugepage_sfd)
+{
+	self->sfd = fsopen("tmpfs", 0);
+	ASSERT_NE(self->sfd, -1);
+}
+
+FIXTURE_TEARDOWN(tmpfs_hugepage_sfd)
+{
+	EXPECT_EQ(close(self->sfd), 0);
+}
+
+TEST_F(tmpfs_hugepage_sfd, restrictedmem_fstat_tmpfs_huge_always)
+{
+	int ret = -1;
+	int fd = -1;
+	int mfd = -1;
+	struct stat stat;
+
+	fsconfig(self->sfd, FSCONFIG_SET_STRING, "huge", "always", 0);
+	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+
+	mfd = fsmount(self->sfd, 0, 0);
+	ASSERT_NE(mfd, -1);
+
+	fd = memfd_restricted(RMFD_USERMNT, mfd);
+	ASSERT_GT(fd, 0);
+
+	/* User can close reference to mount */
+	ret = close(mfd);
+	ASSERT_EQ(ret, 0);
+
+	ret = fstat(fd, &stat);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
+
+	close(fd);
+}
+
+TEST_F(tmpfs_hugepage_sfd, restrictedmem_fstat_tmpfs_huge_never)
+{
+	int ret = -1;
+	int fd = -1;
+	int mfd = -1;
+	struct stat stat;
+
+	fsconfig(self->sfd, FSCONFIG_SET_STRING, "huge", "never", 0);
+	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+
+	mfd = fsmount(self->sfd, 0, 0);
+	ASSERT_NE(mfd, -1);
+
+	fd = memfd_restricted(RMFD_USERMNT, mfd);
+	ASSERT_GT(fd, 0);
+
+	/* User can close reference to mount */
+	ret = close(mfd);
+	ASSERT_EQ(ret, 0);
+
+	ret = fstat(fd, &stat);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(stat.st_blksize, getpagesize());
+
+	close(fd);
+}
+
+TEST_F(tmpfs_hugepage_sfd, restrictedmem_check_mount_flags)
+{
+	int ret = -1;
+	int fd = -1;
+	int mfd = -1;
+
+	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+
+	mfd = fsmount(self->sfd, 0, MOUNT_ATTR_RDONLY);
+	ASSERT_NE(mfd, -1);
+
+	fd = memfd_restricted(RMFD_USERMNT, mfd);
+	ASSERT_EQ(fd, -1);
+	ASSERT_EQ(errno, EROFS);
+
+	ret = close(mfd);
+	ASSERT_EQ(ret, 0);
+}
+
+TEST_F(tmpfs_hugepage_sfd, restrictedmem_check_superblock_flags)
+{
+	int ret = -1;
+	int fd = -1;
+	int mfd = -1;
+
+	fsconfig(self->sfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
+	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+
+	mfd = fsmount(self->sfd, 0, 0);
+	ASSERT_NE(mfd, -1);
+
+	fd = memfd_restricted(RMFD_USERMNT, mfd);
+	ASSERT_EQ(fd, -1);
+	ASSERT_EQ(errno, EROFS);
+
+	ret = close(mfd);
+	ASSERT_EQ(ret, 0);
+}
+
+static bool directory_exists(const char *path)
+{
+	struct stat sb;
+
+	return stat(path, &sb) == 0 && S_ISDIR(sb.st_mode);
+}
+
+FIXTURE(tmpfs_hugepage_mount_path)
+{
+	char *mount_path;
+};
+
+FIXTURE_SETUP(tmpfs_hugepage_mount_path)
+{
+	int ret = -1;
+
+	/* /tmp is an FHS-mandated world-writable directory */
+	self->mount_path = "/tmp/restrictedmem-selftest-mnt";
+
+	if (!directory_exists(self->mount_path)) {
+		ret = mkdir(self->mount_path, 0777);
+		ASSERT_EQ(ret, 0);
+	}
+}
+
+FIXTURE_TEARDOWN(tmpfs_hugepage_mount_path)
+{
+	int ret = -1;
+
+	if (!directory_exists(self->mount_path))
+		return;
+
+	ret = umount2(self->mount_path, MNT_FORCE);
+	EXPECT_EQ(ret, 0);
+	if (ret == -1 && errno == EINVAL)
+		fprintf(stderr, "  %s was not mounted\n", self->mount_path);
+
+	ret = rmdir(self->mount_path);
+	EXPECT_EQ(ret, 0);
+	if (ret == -1)
+		fprintf(stderr, "  rmdir(%s) failed: %m\n", self->mount_path);
+}
+
+/*
+ * memfd_restricted() syscall can only be used with the fd of the root of the
+ * mount. When the restrictedmem's fd is open, a user should not be able to
+ * unmount or remove the mounted directory
+ */
+TEST_F(tmpfs_hugepage_mount_path, restrictedmem_umount_rmdir_while_file_open)
+{
+	int ret = -1;
+	int fd = -1;
+	int mfd = -1;
+	struct stat stat;
+
+	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
+	ASSERT_EQ(ret, 0);
+
+	mfd = open(self->mount_path, O_PATH);
+	ASSERT_NE(mfd, -1);
+
+	fd = memfd_restricted(RMFD_USERMNT, mfd);
+	ASSERT_GT(fd, 0);
+
+	/* We don't need this reference to the mount anymore */
+	ret = close(mfd);
+	ASSERT_EQ(ret, 0);
+
+	/* restrictedmem's fd should still be usable */
+	ret = fstat(fd, &stat);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
+
+	/* User should not be able to unmount directory */
+	ret = umount2(self->mount_path, MNT_FORCE);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EBUSY);
+
+	ret = rmdir(self->mount_path);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EBUSY);
+
+	close(fd);
+}
+
+/* The fd of a file on the mount cannot be provided as mount_fd */
+TEST_F(tmpfs_hugepage_mount_path, restrictedmem_provide_fd_of_file)
+{
+	int ret = -1;
+	int fd = -1;
+	int ffd = -1;
+	char tmp_file_path[PATH_MAX] = { 0 };
+
+	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
+	ASSERT_EQ(ret, 0);
+
+	snprintf(tmp_file_path, PATH_MAX, "%s/tmp-file", self->mount_path);
+	ret = write_string_to_file(tmp_file_path, "filler\n");
+	ASSERT_EQ(ret, 0);
+
+	ffd = open(tmp_file_path, O_RDWR);
+	ASSERT_GT(ffd, 0);
+
+	fd = memfd_restricted(RMFD_USERMNT, ffd);
+	ASSERT_LT(fd, 0);
+	ASSERT_EQ(errno, EINVAL);
+
+	ret = close(ffd);
+	ASSERT_EQ(ret, 0);
+
+	close(fd);
+	remove(tmp_file_path);
+}
+
+/* The fd of files on the mount cannot be provided as mount_fd */
+TEST_F(tmpfs_hugepage_mount_path, restrictedmem_provide_fd_of_file_in_subdir)
+{
+	int ret = -1;
+	int fd = -1;
+	int ffd = -1;
+	char tmp_dir_path[PATH_MAX] = { 0 };
+	char tmp_file_path[PATH_MAX] = { 0 };
+
+	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
+	ASSERT_EQ(ret, 0);
+
+	snprintf(tmp_dir_path, PATH_MAX, "%s/tmp-subdir", self->mount_path);
+	ret = mkdir(tmp_dir_path, 0777);
+	ASSERT_EQ(ret, 0);
+
+	snprintf(tmp_file_path, PATH_MAX, "%s/tmp-subdir/tmp-file",
+		 self->mount_path);
+	ret = write_string_to_file(tmp_file_path, "filler\n");
+	ASSERT_EQ(ret, 0);
+
+	ffd = open(tmp_file_path, O_RDWR);
+	ASSERT_NE(ffd, -1);
+
+	fd = memfd_restricted(RMFD_USERMNT, ffd);
+	ASSERT_LT(fd, 0);
+	ASSERT_EQ(errno, EINVAL);
+
+	ret = close(ffd);
+	ASSERT_EQ(ret, 0);
+
+	close(fd);
+	remove(tmp_file_path);
+	rmdir(tmp_dir_path);
+}
+
+TEST_HARNESS_MAIN
-- 
2.40.0.348.gf938b09366-goog

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[David Hildenbrand]

On 01.04.23 01:50, Ackerley Tng wrote:
> By default, the backing shmem file for a restrictedmem fd is created
> on shmem's kernel space mount.
> 
> With this patch, an optional tmpfs mount can be specified via an fd,
> which will be used as the mountpoint for backing the shmem file
> associated with a restrictedmem fd.
> 
> This will help restrictedmem fds inherit the properties of the
> provided tmpfs mounts, for example, hugepage allocation hints, NUMA
> binding hints, etc.
> 
> Permissions for the fd passed to memfd_restricted() is modeled after
> the openat() syscall, since both of these allow creation of a file
> upon a mount/directory.
> 
> Permission to reference the mount the fd represents is checked upon fd
> creation by other syscalls (e.g. fsmount(), open(), or open_tree(),
> etc) and any process that can present memfd_restricted() with a valid
> fd is expected to have obtained permission to use the mount
> represented by the fd. This behavior is intended to parallel that of
> the openat() syscall.
> 
> memfd_restricted() will check that the tmpfs superblock is
> writable, and that the mount is also writable, before attempting to
> create a restrictedmem file on the mount.
> 
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> ---
>   include/linux/syscalls.h           |  2 +-
>   include/uapi/linux/restrictedmem.h |  8 ++++
>   mm/restrictedmem.c                 | 74 +++++++++++++++++++++++++++---
>   3 files changed, 77 insertions(+), 7 deletions(-)
>   create mode 100644 include/uapi/linux/restrictedmem.h
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index f9e9e0c820c5..a23c4c385cd3 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1056,7 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
>   asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
>   					    unsigned long home_node,
>   					    unsigned long flags);
> -asmlinkage long sys_memfd_restricted(unsigned int flags);
> +asmlinkage long sys_memfd_restricted(unsigned int flags, int mount_fd);
> 
>   /*
>    * Architecture-specific system calls
> diff --git a/include/uapi/linux/restrictedmem.h b/include/uapi/linux/restrictedmem.h
> new file mode 100644
> index 000000000000..22d6f2285f6d
> --- /dev/null
> +++ b/include/uapi/linux/restrictedmem.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_RESTRICTEDMEM_H
> +#define _UAPI_LINUX_RESTRICTEDMEM_H
> +
> +/* flags for memfd_restricted */
> +#define RMFD_USERMNT		0x0001U

I wonder if we can come up with a more expressive prefix than RMFD. 
Sounds more like "rm fd" ;) Maybe it should better match the 
"memfd_restricted" syscall name, like "MEMFD_RSTD_USERMNT".


> +
> +#endif /* _UAPI_LINUX_RESTRICTEDMEM_H */
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index c5d869d8c2d8..f7b62364a31a 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -1,11 +1,12 @@
>   // SPDX-License-Identifier: GPL-2.0
> -#include "linux/sbitmap.h"

Looks like an unrelated change?

> +#include <linux/namei.h>
>   #include <linux/pagemap.h>
>   #include <linux/pseudo_fs.h>
>   #include <linux/shmem_fs.h>
>   #include <linux/syscalls.h>
>   #include <uapi/linux/falloc.h>
>   #include <uapi/linux/magic.h>
> +#include <uapi/linux/restrictedmem.h>
>   #include <linux/restrictedmem.h>
> 
>   struct restrictedmem {
> @@ -189,19 +190,20 @@ static struct file *restrictedmem_file_create(struct file *memfd)
>   	return file;
>   }
> 
> -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> +static int restrictedmem_create(struct vfsmount *mount)
>   {
>   	struct file *file, *restricted_file;
>   	int fd, err;
> 
> -	if (flags)
> -		return -EINVAL;
> -
>   	fd = get_unused_fd_flags(0);
>   	if (fd < 0)
>   		return fd;
> 
> -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +	if (mount)
> +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0, VM_NORESERVE);
> +	else
> +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +
>   	if (IS_ERR(file)) {
>   		err = PTR_ERR(file);
>   		goto err_fd;
> @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>   	return err;
>   }
> 
> +static bool is_shmem_mount(struct vfsmount *mnt)
> +{
> +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;
> +}
> +
> +static bool is_mount_root(struct file *file)
> +{
> +	return file->f_path.dentry == file->f_path.mnt->mnt_root;
> +}

I'd inline at least that function, pretty self-explaining.

> +
> +static int restrictedmem_create_on_user_mount(int mount_fd)
> +{
> +	int ret;
> +	struct fd f;
> +	struct vfsmount *mnt;
> +
> +	f = fdget_raw(mount_fd);
> +	if (!f.file)
> +		return -EBADF;
> +
> +	ret = -EINVAL;
> +	if (!is_mount_root(f.file))
> +		goto out;
> +
> +	mnt = f.file->f_path.mnt;
> +	if (!is_shmem_mount(mnt))
> +		goto out;
> +
> +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);
> +	if (ret)
> +		goto out;
> +
> +	ret = mnt_want_write(mnt);
> +	if (unlikely(ret))
> +		goto out;
> +
> +	ret = restrictedmem_create(mnt);
> +
> +	mnt_drop_write(mnt);
> +out:
> +	fdput(f);
> +
> +	return ret;
> +}
> +
> +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
> +{
> +	if (flags & ~RMFD_USERMNT)
> +		return -EINVAL;
> +
> +	if (flags == RMFD_USERMNT) {
> +		if (mount_fd < 0)
> +			return -EINVAL;
> +
> +		return restrictedmem_create_on_user_mount(mount_fd);
> +	} else {
> +		return restrictedmem_create(NULL);
> +	}


You can drop the else case:

if (flags == RMFD_USERMNT) {
	...
	return restrictedmem_create_on_user_mount(mount_fd);
}
return restrictedmem_create(NULL);


I do wonder if you want to properly check for a flag instead of 
comparing values. Results in a more natural way to deal with flags:

if (flags & RMFD_USERMNT) {

}

> +}
> +
>   int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
>   		       struct restrictedmem_notifier *notifier, bool exclusive)
>   {

The "memfd_restricted" vs. "restrictedmem" terminology is a bit 
unfortunate, but not your fault here.


I'm not a FS person, but it does look good to me.

-- 
Thanks,

David / dhildenb

Re: [RFC PATCH v3 2/2] selftests: restrictedmem: Check hugepage-ness of shmem file backing restrictedmem fd

[David Hildenbrand]

On 01.04.23 01:50, Ackerley Tng wrote:
> For memfd_restricted() calls without a userspace mount, the backing
> file should be the shmem mount in the kernel, and the size of backing
> pages should be as defined by system-wide shmem configuration.
> 
> If a userspace mount is provided, the size of backing pages should be
> as defined in the mount.
> 
> Also includes negative tests for invalid inputs, including fds
> representing read-only superblocks/mounts.
> 

When you talk about "hugepage" in this patch, do you mean THP or 
hugetlb? I suspect thp, so it might be better to spell that out. IIRC, 
there are plans to support actual huge pages in the future, at which 
point "hugepage" terminology could be misleading.

> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> ---
>   tools/testing/selftests/Makefile              |   1 +
>   .../selftests/restrictedmem/.gitignore        |   3 +
>   .../testing/selftests/restrictedmem/Makefile  |  15 +
>   .../testing/selftests/restrictedmem/common.c  |   9 +
>   .../testing/selftests/restrictedmem/common.h  |   8 +
>   .../restrictedmem_hugepage_test.c             | 486 ++++++++++++++++++
>   6 files changed, 522 insertions(+)
>   create mode 100644 tools/testing/selftests/restrictedmem/.gitignore
>   create mode 100644 tools/testing/selftests/restrictedmem/Makefile
>   create mode 100644 tools/testing/selftests/restrictedmem/common.c
>   create mode 100644 tools/testing/selftests/restrictedmem/common.h
>   create mode 100644 tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
> 
> diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
> index f07aef7c592c..44078eeefb79 100644
> --- a/tools/testing/selftests/Makefile
> +++ b/tools/testing/selftests/Makefile
> @@ -60,6 +60,7 @@ TARGETS += pstore
>   TARGETS += ptrace
>   TARGETS += openat2
>   TARGETS += resctrl
> +TARGETS += restrictedmem
>   TARGETS += rlimits
>   TARGETS += rseq
>   TARGETS += rtc
> diff --git a/tools/testing/selftests/restrictedmem/.gitignore b/tools/testing/selftests/restrictedmem/.gitignore
> new file mode 100644
> index 000000000000..2581bcc8ff29
> --- /dev/null
> +++ b/tools/testing/selftests/restrictedmem/.gitignore
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +restrictedmem_hugepage_test
> diff --git a/tools/testing/selftests/restrictedmem/Makefile b/tools/testing/selftests/restrictedmem/Makefile
> new file mode 100644
> index 000000000000..8e5378d20226
> --- /dev/null
> +++ b/tools/testing/selftests/restrictedmem/Makefile
> @@ -0,0 +1,15 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +CFLAGS = $(KHDR_INCLUDES)
> +CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -std=gnu99
> +
> +TEST_GEN_PROGS += restrictedmem_hugepage_test
> +
> +include ../lib.mk
> +
> +EXTRA_CLEAN = $(OUTPUT)/common.o
> +
> +$(OUTPUT)/common.o: common.c
> +	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c -ffreestanding $< -o $@
> +
> +$(TEST_GEN_PROGS): $(OUTPUT)/common.o
> diff --git a/tools/testing/selftests/restrictedmem/common.c b/tools/testing/selftests/restrictedmem/common.c
> new file mode 100644
> index 000000000000..03dac843404f
> --- /dev/null
> +++ b/tools/testing/selftests/restrictedmem/common.c
> @@ -0,0 +1,9 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <sys/syscall.h>
> +#include <unistd.h>
> +
> +int memfd_restricted(unsigned int flags, int mount_fd)
> +{
> +	return syscall(__NR_memfd_restricted, flags, mount_fd);
> +}
> diff --git a/tools/testing/selftests/restrictedmem/common.h b/tools/testing/selftests/restrictedmem/common.h
> new file mode 100644
> index 000000000000..06284ed86baf
> --- /dev/null
> +++ b/tools/testing/selftests/restrictedmem/common.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#ifndef SELFTESTS_RESTRICTEDMEM_COMMON_H
> +#define SELFTESTS_RESTRICTEDMEM_COMMON_H
> +
> +int memfd_restricted(unsigned int flags, int mount_fd);
> +
> +#endif  // SELFTESTS_RESTRICTEDMEM_COMMON_H
> diff --git a/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
> new file mode 100644
> index 000000000000..9ed319b83cb8
> --- /dev/null
> +++ b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
> @@ -0,0 +1,486 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#define _GNU_SOURCE /* for O_PATH */
> +#define _POSIX_C_SOURCE /* for PATH_MAX */
> +#include <limits.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <sys/mman.h>
> +#include <sys/mount.h>
> +#include <sys/stat.h>
> +#include <unistd.h>
> +
> +#include "linux/restrictedmem.h"
> +
> +#include "common.h"
> +#include "../kselftest_harness.h"
> +
> +/*
> + * Expect policy to be one of always, within_size, advise, never,
> + * deny, force
> + */
> +#define POLICY_BUF_SIZE 12
> +
> +static int get_hpage_pmd_size(void)
> +{
> +	FILE *fp;
> +	char buf[100];
> +	char *ret;
> +	int size;
> +
> +	fp = fopen("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", "r");
> +	if (!fp)
> +		return -1;
> +
> +	ret = fgets(buf, 100, fp);
> +	if (ret != buf) {
> +		size = -1;
> +		goto out;
> +	}
> +
> +	if (sscanf(buf, "%d\n", &size) != 1)
> +		size = -1;
> +
> +out:
> +	fclose(fp);
> +
> +	return size;
> +}
> +
> +static bool is_valid_shmem_thp_policy(char *policy)
> +{
> +	if (strcmp(policy, "always") == 0)
> +		return true;
> +	if (strcmp(policy, "within_size") == 0)
> +		return true;
> +	if (strcmp(policy, "advise") == 0)
> +		return true;
> +	if (strcmp(policy, "never") == 0)
> +		return true;
> +	if (strcmp(policy, "deny") == 0)
> +		return true;
> +	if (strcmp(policy, "force") == 0)
> +		return true;
> +
> +	return false;
> +}
> +
> +static int get_shmem_thp_policy(char *policy)
> +{
> +	FILE *fp;
> +	char buf[100];
> +	char *left = NULL;
> +	char *right = NULL;
> +	int ret = -1;
> +
> +	fp = fopen("/sys/kernel/mm/transparent_hugepage/shmem_enabled", "r");
> +	if (!fp)
> +		return -1;
> +
> +	if (fgets(buf, 100, fp) != buf)
> +		goto out;
> +
> +	/*
> +	 * Expect shmem_enabled to be of format like "always within_size advise
> +	 * [never] deny force"
> +	 */
> +	left = memchr(buf, '[', 100);
> +	if (!left)
> +		goto out;
> +
> +	right = memchr(buf, ']', 100);
> +	if (!right)
> +		goto out;
> +
> +	memcpy(policy, left + 1, right - left - 1);
> +
> +	ret = !is_valid_shmem_thp_policy(policy);
> +
> +out:
> +	fclose(fp);
> +	return ret;
> +}
> +
> +static int write_string_to_file(const char *path, const char *string)
> +{
> +	FILE *fp;
> +	size_t len = strlen(string);
> +	int ret = -1;
> +
> +	fp = fopen(path, "w");
> +	if (!fp)
> +		return ret;
> +
> +	if (fwrite(string, 1, len, fp) != len)
> +		goto out;
> +
> +	ret = 0;
> +
> +out:
> +	fclose(fp);
> +	return ret;
> +}
> +
> +static int set_shmem_thp_policy(char *policy)
> +{
> +	int ret = -1;
> +	/* +1 for newline */
> +	char to_write[POLICY_BUF_SIZE + 1] = { 0 };
> +
> +	if (!is_valid_shmem_thp_policy(policy))
> +		return ret;
> +
> +	ret = snprintf(to_write, POLICY_BUF_SIZE + 1, "%s\n", policy);
> +	if (ret != strlen(policy) + 1)
> +		return -1;
> +
> +	ret = write_string_to_file(
> +		"/sys/kernel/mm/transparent_hugepage/shmem_enabled", to_write);
> +
> +	return ret;
> +}
> +
> +FIXTURE(reset_shmem_enabled)
> +{
> +	char shmem_enabled[POLICY_BUF_SIZE];
> +};
> +
> +FIXTURE_SETUP(reset_shmem_enabled)
> +{
> +	memset(self->shmem_enabled, 0, POLICY_BUF_SIZE);
> +	ASSERT_EQ(get_shmem_thp_policy(self->shmem_enabled), 0);
> +}
> +
> +FIXTURE_TEARDOWN(reset_shmem_enabled)
> +{
> +	ASSERT_EQ(set_shmem_thp_policy(self->shmem_enabled), 0);
> +}
> +
> +TEST_F(reset_shmem_enabled, restrictedmem_fstat_shmem_enabled_never)
> +{
> +	int fd = -1;
> +	struct stat stat;
> +
> +	ASSERT_EQ(set_shmem_thp_policy("never"), 0);
> +
> +	fd = memfd_restricted(0, -1);
> +	ASSERT_GT(fd, 0);
> +
> +	ASSERT_EQ(fstat(fd, &stat), 0);
> +
> +	/*
> +	 * st_blksize is set based on the superblock's s_blocksize_bits. For
> +	 * shmem, this is set to PAGE_SHIFT
> +	 */
> +	ASSERT_EQ(stat.st_blksize, getpagesize());
> +
> +	close(fd);
> +}
> +
> +TEST_F(reset_shmem_enabled, restrictedmem_fstat_shmem_enabled_always)
> +{
> +	int fd = -1;
> +	struct stat stat;
> +
> +	ASSERT_EQ(set_shmem_thp_policy("always"), 0);
> +
> +	fd = memfd_restricted(0, -1);
> +	ASSERT_GT(fd, 0);
> +
> +	ASSERT_EQ(fstat(fd, &stat), 0);
> +
> +	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
> +
> +	close(fd);
> +}
> +
> +TEST(restrictedmem_tmpfile_invalid_fd)
> +{
> +	int fd = memfd_restricted(RMFD_USERMNT, -2);
> +
> +	ASSERT_EQ(fd, -1);
> +	ASSERT_EQ(errno, EINVAL);
> +}
> +
> +TEST(restrictedmem_tmpfile_fd_not_a_mount)
> +{
> +	int fd = memfd_restricted(RMFD_USERMNT, STDOUT_FILENO);
> +
> +	ASSERT_EQ(fd, -1);
> +	ASSERT_EQ(errno, EINVAL);
> +}
> +
> +TEST(restrictedmem_tmpfile_not_tmpfs_mount)
> +{
> +	int fd = -1;
> +	int mfd = -1;
> +
> +	mfd = open("/proc", O_PATH);
> +	ASSERT_NE(mfd, -1);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, mfd);
> +
> +	ASSERT_EQ(fd, -1);
> +	ASSERT_EQ(errno, EINVAL);
> +}
> +
> +FIXTURE(tmpfs_hugepage_sfd)
> +{
> +	int sfd;
> +};
> +
> +FIXTURE_SETUP(tmpfs_hugepage_sfd)
> +{
> +	self->sfd = fsopen("tmpfs", 0);
> +	ASSERT_NE(self->sfd, -1);
> +}
> +
> +FIXTURE_TEARDOWN(tmpfs_hugepage_sfd)
> +{
> +	EXPECT_EQ(close(self->sfd), 0);
> +}
> +
> +TEST_F(tmpfs_hugepage_sfd, restrictedmem_fstat_tmpfs_huge_always)
> +{
> +	int ret = -1;
> +	int fd = -1;
> +	int mfd = -1;
> +	struct stat stat;
> +
> +	fsconfig(self->sfd, FSCONFIG_SET_STRING, "huge", "always", 0);
> +	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> +
> +	mfd = fsmount(self->sfd, 0, 0);
> +	ASSERT_NE(mfd, -1);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, mfd);
> +	ASSERT_GT(fd, 0);
> +
> +	/* User can close reference to mount */
> +	ret = close(mfd);
> +	ASSERT_EQ(ret, 0);
> +
> +	ret = fstat(fd, &stat);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
> +
> +	close(fd);
> +}
> +
> +TEST_F(tmpfs_hugepage_sfd, restrictedmem_fstat_tmpfs_huge_never)
> +{
> +	int ret = -1;
> +	int fd = -1;
> +	int mfd = -1;
> +	struct stat stat;
> +
> +	fsconfig(self->sfd, FSCONFIG_SET_STRING, "huge", "never", 0);
> +	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> +
> +	mfd = fsmount(self->sfd, 0, 0);
> +	ASSERT_NE(mfd, -1);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, mfd);
> +	ASSERT_GT(fd, 0);
> +
> +	/* User can close reference to mount */
> +	ret = close(mfd);
> +	ASSERT_EQ(ret, 0);
> +
> +	ret = fstat(fd, &stat);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(stat.st_blksize, getpagesize());
> +
> +	close(fd);
> +}
> +
> +TEST_F(tmpfs_hugepage_sfd, restrictedmem_check_mount_flags)
> +{
> +	int ret = -1;
> +	int fd = -1;
> +	int mfd = -1;
> +
> +	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> +
> +	mfd = fsmount(self->sfd, 0, MOUNT_ATTR_RDONLY);
> +	ASSERT_NE(mfd, -1);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, mfd);
> +	ASSERT_EQ(fd, -1);
> +	ASSERT_EQ(errno, EROFS);
> +
> +	ret = close(mfd);
> +	ASSERT_EQ(ret, 0);
> +}
> +
> +TEST_F(tmpfs_hugepage_sfd, restrictedmem_check_superblock_flags)
> +{
> +	int ret = -1;
> +	int fd = -1;
> +	int mfd = -1;
> +
> +	fsconfig(self->sfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
> +	fsconfig(self->sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> +
> +	mfd = fsmount(self->sfd, 0, 0);
> +	ASSERT_NE(mfd, -1);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, mfd);
> +	ASSERT_EQ(fd, -1);
> +	ASSERT_EQ(errno, EROFS);
> +
> +	ret = close(mfd);
> +	ASSERT_EQ(ret, 0);
> +}
> +
> +static bool directory_exists(const char *path)
> +{
> +	struct stat sb;
> +
> +	return stat(path, &sb) == 0 && S_ISDIR(sb.st_mode);
> +}
> +
> +FIXTURE(tmpfs_hugepage_mount_path)
> +{
> +	char *mount_path;
> +};
> +
> +FIXTURE_SETUP(tmpfs_hugepage_mount_path)
> +{
> +	int ret = -1;
> +
> +	/* /tmp is an FHS-mandated world-writable directory */
> +	self->mount_path = "/tmp/restrictedmem-selftest-mnt";
> +
> +	if (!directory_exists(self->mount_path)) {
> +		ret = mkdir(self->mount_path, 0777);
> +		ASSERT_EQ(ret, 0);
> +	}
> +}
> +
> +FIXTURE_TEARDOWN(tmpfs_hugepage_mount_path)
> +{
> +	int ret = -1;
> +
> +	if (!directory_exists(self->mount_path))
> +		return;
> +
> +	ret = umount2(self->mount_path, MNT_FORCE);
> +	EXPECT_EQ(ret, 0);
> +	if (ret == -1 && errno == EINVAL)
> +		fprintf(stderr, "  %s was not mounted\n", self->mount_path);
> +
> +	ret = rmdir(self->mount_path);
> +	EXPECT_EQ(ret, 0);
> +	if (ret == -1)
> +		fprintf(stderr, "  rmdir(%s) failed: %m\n", self->mount_path);
> +}
> +
> +/*
> + * memfd_restricted() syscall can only be used with the fd of the root of the
> + * mount. When the restrictedmem's fd is open, a user should not be able to
> + * unmount or remove the mounted directory
> + */
> +TEST_F(tmpfs_hugepage_mount_path, restrictedmem_umount_rmdir_while_file_open)
> +{
> +	int ret = -1;
> +	int fd = -1;
> +	int mfd = -1;
> +	struct stat stat;
> +
> +	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
> +	ASSERT_EQ(ret, 0);
> +
> +	mfd = open(self->mount_path, O_PATH);
> +	ASSERT_NE(mfd, -1);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, mfd);
> +	ASSERT_GT(fd, 0);
> +
> +	/* We don't need this reference to the mount anymore */
> +	ret = close(mfd);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* restrictedmem's fd should still be usable */
> +	ret = fstat(fd, &stat);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
> +
> +	/* User should not be able to unmount directory */
> +	ret = umount2(self->mount_path, MNT_FORCE);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EBUSY);
> +
> +	ret = rmdir(self->mount_path);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EBUSY);
> +
> +	close(fd);
> +}
> +
> +/* The fd of a file on the mount cannot be provided as mount_fd */
> +TEST_F(tmpfs_hugepage_mount_path, restrictedmem_provide_fd_of_file)
> +{
> +	int ret = -1;
> +	int fd = -1;
> +	int ffd = -1;
> +	char tmp_file_path[PATH_MAX] = { 0 };
> +
> +	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
> +	ASSERT_EQ(ret, 0);
> +
> +	snprintf(tmp_file_path, PATH_MAX, "%s/tmp-file", self->mount_path);
> +	ret = write_string_to_file(tmp_file_path, "filler\n");
> +	ASSERT_EQ(ret, 0);
> +
> +	ffd = open(tmp_file_path, O_RDWR);
> +	ASSERT_GT(ffd, 0);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, ffd);
> +	ASSERT_LT(fd, 0);
> +	ASSERT_EQ(errno, EINVAL);
> +
> +	ret = close(ffd);
> +	ASSERT_EQ(ret, 0);
> +
> +	close(fd);
> +	remove(tmp_file_path);
> +}
> +
> +/* The fd of files on the mount cannot be provided as mount_fd */
> +TEST_F(tmpfs_hugepage_mount_path, restrictedmem_provide_fd_of_file_in_subdir)
> +{
> +	int ret = -1;
> +	int fd = -1;
> +	int ffd = -1;
> +	char tmp_dir_path[PATH_MAX] = { 0 };
> +	char tmp_file_path[PATH_MAX] = { 0 };
> +
> +	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
> +	ASSERT_EQ(ret, 0);
> +
> +	snprintf(tmp_dir_path, PATH_MAX, "%s/tmp-subdir", self->mount_path);
> +	ret = mkdir(tmp_dir_path, 0777);
> +	ASSERT_EQ(ret, 0);
> +
> +	snprintf(tmp_file_path, PATH_MAX, "%s/tmp-subdir/tmp-file",
> +		 self->mount_path);
> +	ret = write_string_to_file(tmp_file_path, "filler\n");
> +	ASSERT_EQ(ret, 0);
> +
> +	ffd = open(tmp_file_path, O_RDWR);
> +	ASSERT_NE(ffd, -1);
> +
> +	fd = memfd_restricted(RMFD_USERMNT, ffd);
> +	ASSERT_LT(fd, 0);
> +	ASSERT_EQ(errno, EINVAL);
> +
> +	ret = close(ffd);
> +	ASSERT_EQ(ret, 0);
> +
> +	close(fd);
> +	remove(tmp_file_path);
> +	rmdir(tmp_dir_path);
> +}
> +
> +TEST_HARNESS_MAIN

-- 
Thanks,

David / dhildenb

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Kirill A. Shutemov]

On Fri, Mar 31, 2023 at 11:50:39PM +0000, Ackerley Tng wrote:
> By default, the backing shmem file for a restrictedmem fd is created
> on shmem's kernel space mount.
> 
> With this patch, an optional tmpfs mount can be specified via an fd,
> which will be used as the mountpoint for backing the shmem file
> associated with a restrictedmem fd.
> 
> This will help restrictedmem fds inherit the properties of the
> provided tmpfs mounts, for example, hugepage allocation hints, NUMA
> binding hints, etc.
> 
> Permissions for the fd passed to memfd_restricted() is modeled after
> the openat() syscall, since both of these allow creation of a file
> upon a mount/directory.
> 
> Permission to reference the mount the fd represents is checked upon fd
> creation by other syscalls (e.g. fsmount(), open(), or open_tree(),
> etc) and any process that can present memfd_restricted() with a valid
> fd is expected to have obtained permission to use the mount
> represented by the fd. This behavior is intended to parallel that of
> the openat() syscall.
> 
> memfd_restricted() will check that the tmpfs superblock is
> writable, and that the mount is also writable, before attempting to
> create a restrictedmem file on the mount.
> 
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> ---
>  include/linux/syscalls.h           |  2 +-
>  include/uapi/linux/restrictedmem.h |  8 ++++
>  mm/restrictedmem.c                 | 74 +++++++++++++++++++++++++++---
>  3 files changed, 77 insertions(+), 7 deletions(-)
>  create mode 100644 include/uapi/linux/restrictedmem.h
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index f9e9e0c820c5..a23c4c385cd3 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1056,7 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
>  asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
>  					    unsigned long home_node,
>  					    unsigned long flags);
> -asmlinkage long sys_memfd_restricted(unsigned int flags);
> +asmlinkage long sys_memfd_restricted(unsigned int flags, int mount_fd);
> 
>  /*
>   * Architecture-specific system calls
> diff --git a/include/uapi/linux/restrictedmem.h b/include/uapi/linux/restrictedmem.h
> new file mode 100644
> index 000000000000..22d6f2285f6d
> --- /dev/null
> +++ b/include/uapi/linux/restrictedmem.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_RESTRICTEDMEM_H
> +#define _UAPI_LINUX_RESTRICTEDMEM_H
> +
> +/* flags for memfd_restricted */
> +#define RMFD_USERMNT		0x0001U
> +
> +#endif /* _UAPI_LINUX_RESTRICTEDMEM_H */
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index c5d869d8c2d8..f7b62364a31a 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -1,11 +1,12 @@
>  // SPDX-License-Identifier: GPL-2.0
> -#include "linux/sbitmap.h"
> +#include <linux/namei.h>
>  #include <linux/pagemap.h>
>  #include <linux/pseudo_fs.h>
>  #include <linux/shmem_fs.h>
>  #include <linux/syscalls.h>
>  #include <uapi/linux/falloc.h>
>  #include <uapi/linux/magic.h>
> +#include <uapi/linux/restrictedmem.h>
>  #include <linux/restrictedmem.h>
> 
>  struct restrictedmem {
> @@ -189,19 +190,20 @@ static struct file *restrictedmem_file_create(struct file *memfd)
>  	return file;
>  }
> 
> -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> +static int restrictedmem_create(struct vfsmount *mount)
>  {
>  	struct file *file, *restricted_file;
>  	int fd, err;
> 
> -	if (flags)
> -		return -EINVAL;
> -
>  	fd = get_unused_fd_flags(0);
>  	if (fd < 0)
>  		return fd;
> 
> -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +	if (mount)
> +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0, VM_NORESERVE);
> +	else
> +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +
>  	if (IS_ERR(file)) {
>  		err = PTR_ERR(file);
>  		goto err_fd;
> @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>  	return err;
>  }
> 
> +static bool is_shmem_mount(struct vfsmount *mnt)
> +{
> +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;
> +}
> +
> +static bool is_mount_root(struct file *file)
> +{
> +	return file->f_path.dentry == file->f_path.mnt->mnt_root;
> +}
> +
> +static int restrictedmem_create_on_user_mount(int mount_fd)
> +{
> +	int ret;
> +	struct fd f;
> +	struct vfsmount *mnt;
> +
> +	f = fdget_raw(mount_fd);
> +	if (!f.file)
> +		return -EBADF;
> +
> +	ret = -EINVAL;
> +	if (!is_mount_root(f.file))
> +		goto out;
> +
> +	mnt = f.file->f_path.mnt;
> +	if (!is_shmem_mount(mnt))
> +		goto out;
> +
> +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);

Why MAY_EXEC?

> +	if (ret)
> +		goto out;
> +
> +	ret = mnt_want_write(mnt);
> +	if (unlikely(ret))
> +		goto out;
> +
> +	ret = restrictedmem_create(mnt);
> +
> +	mnt_drop_write(mnt);
> +out:
> +	fdput(f);
> +
> +	return ret;
> +}

We need review from fs folks. Look mostly sensible, but I have no
experience in fs.

> +
> +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
> +{
> +	if (flags & ~RMFD_USERMNT)
> +		return -EINVAL;
> +
> +	if (flags == RMFD_USERMNT) {
> +		if (mount_fd < 0)
> +			return -EINVAL;
> +
> +		return restrictedmem_create_on_user_mount(mount_fd);
> +	} else {
> +		return restrictedmem_create(NULL);
> +	}

Maybe restructure with single restrictedmem_create() call?

	struct vfsmount *mnt = NULL;

	if (flags == RMFD_USERMNT) {
		...
		mnt = ...();
	}

	return restrictedmem_create(mnt);
> +}
> +
>  int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
>  		       struct restrictedmem_notifier *notifier, bool exclusive)
>  {
> --
> 2.40.0.348.gf938b09366-goog

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Christian Brauner]

On Fri, Mar 31, 2023 at 11:50:39PM +0000, Ackerley Tng wrote:
> By default, the backing shmem file for a restrictedmem fd is created
> on shmem's kernel space mount.
> 
> With this patch, an optional tmpfs mount can be specified via an fd,
> which will be used as the mountpoint for backing the shmem file
> associated with a restrictedmem fd.
> 
> This will help restrictedmem fds inherit the properties of the
> provided tmpfs mounts, for example, hugepage allocation hints, NUMA
> binding hints, etc.
> 
> Permissions for the fd passed to memfd_restricted() is modeled after
> the openat() syscall, since both of these allow creation of a file
> upon a mount/directory.
> 
> Permission to reference the mount the fd represents is checked upon fd
> creation by other syscalls (e.g. fsmount(), open(), or open_tree(),
> etc) and any process that can present memfd_restricted() with a valid
> fd is expected to have obtained permission to use the mount
> represented by the fd. This behavior is intended to parallel that of
> the openat() syscall.
> 
> memfd_restricted() will check that the tmpfs superblock is
> writable, and that the mount is also writable, before attempting to
> create a restrictedmem file on the mount.
> 
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> ---
>  include/linux/syscalls.h           |  2 +-
>  include/uapi/linux/restrictedmem.h |  8 ++++
>  mm/restrictedmem.c                 | 74 +++++++++++++++++++++++++++---
>  3 files changed, 77 insertions(+), 7 deletions(-)
>  create mode 100644 include/uapi/linux/restrictedmem.h
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index f9e9e0c820c5..a23c4c385cd3 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1056,7 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
>  asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
>  					    unsigned long home_node,
>  					    unsigned long flags);
> -asmlinkage long sys_memfd_restricted(unsigned int flags);
> +asmlinkage long sys_memfd_restricted(unsigned int flags, int mount_fd);
> 
>  /*
>   * Architecture-specific system calls
> diff --git a/include/uapi/linux/restrictedmem.h b/include/uapi/linux/restrictedmem.h
> new file mode 100644
> index 000000000000..22d6f2285f6d
> --- /dev/null
> +++ b/include/uapi/linux/restrictedmem.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_RESTRICTEDMEM_H
> +#define _UAPI_LINUX_RESTRICTEDMEM_H
> +
> +/* flags for memfd_restricted */
> +#define RMFD_USERMNT		0x0001U
> +
> +#endif /* _UAPI_LINUX_RESTRICTEDMEM_H */
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index c5d869d8c2d8..f7b62364a31a 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -1,11 +1,12 @@
>  // SPDX-License-Identifier: GPL-2.0
> -#include "linux/sbitmap.h"
> +#include <linux/namei.h>
>  #include <linux/pagemap.h>
>  #include <linux/pseudo_fs.h>
>  #include <linux/shmem_fs.h>
>  #include <linux/syscalls.h>
>  #include <uapi/linux/falloc.h>
>  #include <uapi/linux/magic.h>
> +#include <uapi/linux/restrictedmem.h>
>  #include <linux/restrictedmem.h>
> 
>  struct restrictedmem {
> @@ -189,19 +190,20 @@ static struct file *restrictedmem_file_create(struct file *memfd)
>  	return file;
>  }
> 
> -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> +static int restrictedmem_create(struct vfsmount *mount)
>  {
>  	struct file *file, *restricted_file;
>  	int fd, err;
> 
> -	if (flags)
> -		return -EINVAL;
> -
>  	fd = get_unused_fd_flags(0);

Any reasons the file descriptors aren't O_CLOEXEC by default? I don't
see any reasons why we should introduce new fdtypes that aren't
O_CLOEXEC by default. The "don't mix-and-match" train has already left
the station anyway as we do have seccomp noitifer fds and pidfds both of
which are O_CLOEXEC by default.

>  	if (fd < 0)
>  		return fd;
> 
> -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +	if (mount)
> +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0, VM_NORESERVE);
> +	else
> +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +
>  	if (IS_ERR(file)) {
>  		err = PTR_ERR(file);
>  		goto err_fd;
> @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>  	return err;
>  }
> 
> +static bool is_shmem_mount(struct vfsmount *mnt)
> +{
> +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;

This can just be if (mnt->mnt_sb->s_magic == TMPFS_MAGIC).

> +}
> +
> +static bool is_mount_root(struct file *file)
> +{
> +	return file->f_path.dentry == file->f_path.mnt->mnt_root;

mount -t tmpfs tmpfs /mnt
touch /mnt/bla
touch /mnt/ble
mount --bind /mnt/bla /mnt/ble
fd = open("/mnt/ble")
fd_restricted = memfd_restricted(fd)

IOW, this doesn't restrict it to the tmpfs root. It only restricts it to
paths that refer to the root of any tmpfs mount. To exclude bind-mounts
that aren't bind-mounts of the whole filesystem you want:

path->dentry == path->mnt->mnt_root && 
path->mnt->mnt_root == path->mnt->mnt_sb->s_root

> +}
> +
> +static int restrictedmem_create_on_user_mount(int mount_fd)
> +{
> +	int ret;
> +	struct fd f;
> +	struct vfsmount *mnt;
> +
> +	f = fdget_raw(mount_fd);
> +	if (!f.file)
> +		return -EBADF;
> +
> +	ret = -EINVAL;
> +	if (!is_mount_root(f.file))
> +		goto out;
> +
> +	mnt = f.file->f_path.mnt;
> +	if (!is_shmem_mount(mnt))
> +		goto out;
> +
> +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);

With the current semantics you're asking whether you have write
permissions on the /mnt/ble file in order to get answer to the question
whether you're allowed to create an unlinked restricted memory file.
That doesn't make much sense afaict.

> +	if (ret)
> +		goto out;
> +
> +	ret = mnt_want_write(mnt);
> +	if (unlikely(ret))
> +		goto out;
> +
> +	ret = restrictedmem_create(mnt);
> +
> +	mnt_drop_write(mnt);
> +out:
> +	fdput(f);
> +
> +	return ret;
> +}
> +
> +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
> +{
> +	if (flags & ~RMFD_USERMNT)
> +		return -EINVAL;
> +
> +	if (flags == RMFD_USERMNT) {

Why do you even need this flag? It seems that @mount_fd being < 0 is
sufficient to indicate that a new restricted memory fd is supposed to be
created in the system instance.

> +		if (mount_fd < 0)
> +			return -EINVAL;
> +
> +		return restrictedmem_create_on_user_mount(mount_fd);
> +	} else {
> +		return restrictedmem_create(NULL);
> +	}
> +}

I have to say that I'm very confused by all of this the more I look at it.

Effectively memfd restricted functions as a wrapper filesystem around
the tmpfs filesystem. This is basically a weird overlay filesystem.
You're allocating tmpfs files that you stash in restrictedmem files. 
I have to say that this seems very hacky. I didn't get this at all at
first.

So what does the caller get if they call statx() on a restricted memfd?
Do they get the device number of the tmpfs mount and the inode numbers
of the tmpfs mount? Because it looks like they would:

static int restrictedmem_getattr(struct user_namespace *mnt_userns,
				 const struct path *path, struct kstat *stat,
				 u32 request_mask, unsigned int query_flags)
{
	struct inode *inode = d_inode(path->dentry);
	struct restrictedmem *rm = inode->i_mapping->private_data;
	struct file *memfd = rm->memfd;

	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
					     request_mask, query_flags);

That @memfd would be a struct file allocated in a tmpfs instance, no? So
you'd be calling the inode operation of the tmpfs file meaning that
struct kstat will be filled up with the info from the tmpfs instance.

But then if I call statfs() and check the fstype I would get
RESTRICTEDMEM_MAGIC, no? This is... unorthodox?

I'm honestly puzzled and this sounds really strange. There must be a
better way to implement all of this.

Shouldn't you try and make this a part of tmpfs proper? Make a really
separate filesystem and add a memfs library that both tmpfs and
restrictedmemfs can use? Add a mount option to tmpfs that makes it a
restricted tmpfs?

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Christian Brauner]

On Tue, Apr 04, 2023 at 03:53:13PM +0200, Christian Brauner wrote:
> On Fri, Mar 31, 2023 at 11:50:39PM +0000, Ackerley Tng wrote:
> > By default, the backing shmem file for a restrictedmem fd is created
> > on shmem's kernel space mount.
> > 
> > With this patch, an optional tmpfs mount can be specified via an fd,
> > which will be used as the mountpoint for backing the shmem file
> > associated with a restrictedmem fd.
> > 
> > This will help restrictedmem fds inherit the properties of the
> > provided tmpfs mounts, for example, hugepage allocation hints, NUMA
> > binding hints, etc.
> > 
> > Permissions for the fd passed to memfd_restricted() is modeled after
> > the openat() syscall, since both of these allow creation of a file
> > upon a mount/directory.
> > 
> > Permission to reference the mount the fd represents is checked upon fd
> > creation by other syscalls (e.g. fsmount(), open(), or open_tree(),
> > etc) and any process that can present memfd_restricted() with a valid
> > fd is expected to have obtained permission to use the mount
> > represented by the fd. This behavior is intended to parallel that of
> > the openat() syscall.
> > 
> > memfd_restricted() will check that the tmpfs superblock is
> > writable, and that the mount is also writable, before attempting to
> > create a restrictedmem file on the mount.
> > 
> > Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> > ---
> >  include/linux/syscalls.h           |  2 +-
> >  include/uapi/linux/restrictedmem.h |  8 ++++
> >  mm/restrictedmem.c                 | 74 +++++++++++++++++++++++++++---
> >  3 files changed, 77 insertions(+), 7 deletions(-)
> >  create mode 100644 include/uapi/linux/restrictedmem.h
> > 
> > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > index f9e9e0c820c5..a23c4c385cd3 100644
> > --- a/include/linux/syscalls.h
> > +++ b/include/linux/syscalls.h
> > @@ -1056,7 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
> >  asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
> >  					    unsigned long home_node,
> >  					    unsigned long flags);
> > -asmlinkage long sys_memfd_restricted(unsigned int flags);
> > +asmlinkage long sys_memfd_restricted(unsigned int flags, int mount_fd);
> > 
> >  /*
> >   * Architecture-specific system calls
> > diff --git a/include/uapi/linux/restrictedmem.h b/include/uapi/linux/restrictedmem.h
> > new file mode 100644
> > index 000000000000..22d6f2285f6d
> > --- /dev/null
> > +++ b/include/uapi/linux/restrictedmem.h
> > @@ -0,0 +1,8 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +#ifndef _UAPI_LINUX_RESTRICTEDMEM_H
> > +#define _UAPI_LINUX_RESTRICTEDMEM_H
> > +
> > +/* flags for memfd_restricted */
> > +#define RMFD_USERMNT		0x0001U
> > +
> > +#endif /* _UAPI_LINUX_RESTRICTEDMEM_H */
> > diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> > index c5d869d8c2d8..f7b62364a31a 100644
> > --- a/mm/restrictedmem.c
> > +++ b/mm/restrictedmem.c
> > @@ -1,11 +1,12 @@
> >  // SPDX-License-Identifier: GPL-2.0
> > -#include "linux/sbitmap.h"
> > +#include <linux/namei.h>
> >  #include <linux/pagemap.h>
> >  #include <linux/pseudo_fs.h>
> >  #include <linux/shmem_fs.h>
> >  #include <linux/syscalls.h>
> >  #include <uapi/linux/falloc.h>
> >  #include <uapi/linux/magic.h>
> > +#include <uapi/linux/restrictedmem.h>
> >  #include <linux/restrictedmem.h>
> > 
> >  struct restrictedmem {
> > @@ -189,19 +190,20 @@ static struct file *restrictedmem_file_create(struct file *memfd)
> >  	return file;
> >  }
> > 
> > -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> > +static int restrictedmem_create(struct vfsmount *mount)
> >  {
> >  	struct file *file, *restricted_file;
> >  	int fd, err;
> > 
> > -	if (flags)
> > -		return -EINVAL;
> > -
> >  	fd = get_unused_fd_flags(0);
> 
> Any reasons the file descriptors aren't O_CLOEXEC by default? I don't
> see any reasons why we should introduce new fdtypes that aren't
> O_CLOEXEC by default. The "don't mix-and-match" train has already left
> the station anyway as we do have seccomp noitifer fds and pidfds both of
> which are O_CLOEXEC by default.
> 
> >  	if (fd < 0)
> >  		return fd;
> > 
> > -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> > +	if (mount)
> > +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0, VM_NORESERVE);
> > +	else
> > +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> > +
> >  	if (IS_ERR(file)) {
> >  		err = PTR_ERR(file);
> >  		goto err_fd;
> > @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> >  	return err;
> >  }
> > 
> > +static bool is_shmem_mount(struct vfsmount *mnt)
> > +{
> > +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;
> 
> This can just be if (mnt->mnt_sb->s_magic == TMPFS_MAGIC).
> 
> > +}
> > +
> > +static bool is_mount_root(struct file *file)
> > +{
> > +	return file->f_path.dentry == file->f_path.mnt->mnt_root;
> 
> mount -t tmpfs tmpfs /mnt
> touch /mnt/bla
> touch /mnt/ble
> mount --bind /mnt/bla /mnt/ble
> fd = open("/mnt/ble")
> fd_restricted = memfd_restricted(fd)
> 
> IOW, this doesn't restrict it to the tmpfs root. It only restricts it to
> paths that refer to the root of any tmpfs mount. To exclude bind-mounts
> that aren't bind-mounts of the whole filesystem you want:
> 
> path->dentry == path->mnt->mnt_root && 
> path->mnt->mnt_root == path->mnt->mnt_sb->s_root
> 
> > +}
> > +
> > +static int restrictedmem_create_on_user_mount(int mount_fd)
> > +{
> > +	int ret;
> > +	struct fd f;
> > +	struct vfsmount *mnt;
> > +
> > +	f = fdget_raw(mount_fd);
> > +	if (!f.file)
> > +		return -EBADF;
> > +
> > +	ret = -EINVAL;
> > +	if (!is_mount_root(f.file))
> > +		goto out;
> > +
> > +	mnt = f.file->f_path.mnt;
> > +	if (!is_shmem_mount(mnt))
> > +		goto out;
> > +
> > +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);
> 
> With the current semantics you're asking whether you have write
> permissions on the /mnt/ble file in order to get answer to the question
> whether you're allowed to create an unlinked restricted memory file.
> That doesn't make much sense afaict.
> 
> > +	if (ret)
> > +		goto out;
> > +
> > +	ret = mnt_want_write(mnt);
> > +	if (unlikely(ret))
> > +		goto out;
> > +
> > +	ret = restrictedmem_create(mnt);
> > +
> > +	mnt_drop_write(mnt);
> > +out:
> > +	fdput(f);
> > +
> > +	return ret;
> > +}
> > +
> > +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
> > +{
> > +	if (flags & ~RMFD_USERMNT)
> > +		return -EINVAL;
> > +
> > +	if (flags == RMFD_USERMNT) {
> 
> Why do you even need this flag? It seems that @mount_fd being < 0 is
> sufficient to indicate that a new restricted memory fd is supposed to be
> created in the system instance.
> 
> > +		if (mount_fd < 0)
> > +			return -EINVAL;
> > +
> > +		return restrictedmem_create_on_user_mount(mount_fd);
> > +	} else {
> > +		return restrictedmem_create(NULL);
> > +	}
> > +}
> 
> I have to say that I'm very confused by all of this the more I look at it.
> 
> Effectively memfd restricted functions as a wrapper filesystem around
> the tmpfs filesystem. This is basically a weird overlay filesystem.
> You're allocating tmpfs files that you stash in restrictedmem files. 
> I have to say that this seems very hacky. I didn't get this at all at
> first.
> 
> So what does the caller get if they call statx() on a restricted memfd?
> Do they get the device number of the tmpfs mount and the inode numbers
> of the tmpfs mount? Because it looks like they would:
> 
> static int restrictedmem_getattr(struct user_namespace *mnt_userns,
> 				 const struct path *path, struct kstat *stat,
> 				 u32 request_mask, unsigned int query_flags)
> {
> 	struct inode *inode = d_inode(path->dentry);
> 	struct restrictedmem *rm = inode->i_mapping->private_data;
> 	struct file *memfd = rm->memfd;
> 
> 	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,

This is pretty broken btw, because @path refers to a restrictedmem path
which you're passing to a tmpfs iop...

I see that in

	return memfd->f_inode->i_op->getattr(mnt_userns, &memfd->f_path, stat,
					     request_mask, query_flags);

this if fixed but still, this is... not great.

> 					     request_mask, query_flags);
> 
> That @memfd would be a struct file allocated in a tmpfs instance, no? So
> you'd be calling the inode operation of the tmpfs file meaning that
> struct kstat will be filled up with the info from the tmpfs instance.
> 
> But then if I call statfs() and check the fstype I would get
> RESTRICTEDMEM_MAGIC, no? This is... unorthodox?
> 
> I'm honestly puzzled and this sounds really strange. There must be a
> better way to implement all of this.
> 
> Shouldn't you try and make this a part of tmpfs proper? Make a really
> separate filesystem and add a memfs library that both tmpfs and
> restrictedmemfs can use? Add a mount option to tmpfs that makes it a
> restricted tmpfs?

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Ackerley Tng]

Thanks again for your review!

Christian Brauner <brauner@kernel.org> writes:
> On Tue, Apr 04, 2023 at 03:53:13PM +0200, Christian Brauner wrote:
>> On Fri, Mar 31, 2023 at 11:50:39PM +0000, Ackerley Tng wrote:
>> >
>> > ...
>> >
>> > -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>> > +static int restrictedmem_create(struct vfsmount *mount)
>> >  {
>> >  	struct file *file, *restricted_file;
>> >  	int fd, err;
>> >
>> > -	if (flags)
>> > -		return -EINVAL;
>> > -
>> >  	fd = get_unused_fd_flags(0);

>> Any reasons the file descriptors aren't O_CLOEXEC by default? I don't
>> see any reasons why we should introduce new fdtypes that aren't
>> O_CLOEXEC by default. The "don't mix-and-match" train has already left
>> the station anyway as we do have seccomp noitifer fds and pidfds both of
>> which are O_CLOEXEC by default.


Thanks for pointing this out. I agree with using O_CLOEXEC, but didn’t
notice this before. Let us discuss this under the original series at
[1].

>> >  	if (fd < 0)
>> >  		return fd;
>> >
>> > -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
>> > +	if (mount)
>> > +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0,  
>> VM_NORESERVE);
>> > +	else
>> > +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
>> > +
>> >  	if (IS_ERR(file)) {
>> >  		err = PTR_ERR(file);
>> >  		goto err_fd;
>> > @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int,  
>> flags)
>> >  	return err;
>> >  }
>> >
>> > +static bool is_shmem_mount(struct vfsmount *mnt)
>> > +{
>> > +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;

>> This can just be if (mnt->mnt_sb->s_magic == TMPFS_MAGIC).


Will simplify this in the next revision.

>> > +}
>> > +
>> > +static bool is_mount_root(struct file *file)
>> > +{
>> > +	return file->f_path.dentry == file->f_path.mnt->mnt_root;

>> mount -t tmpfs tmpfs /mnt
>> touch /mnt/bla
>> touch /mnt/ble
>> mount --bind /mnt/bla /mnt/ble
>> fd = open("/mnt/ble")
>> fd_restricted = memfd_restricted(fd)

>> IOW, this doesn't restrict it to the tmpfs root. It only restricts it to
>> paths that refer to the root of any tmpfs mount. To exclude bind-mounts
>> that aren't bind-mounts of the whole filesystem you want:

>> path->dentry == path->mnt->mnt_root &&
>> path->mnt->mnt_root == path->mnt->mnt_sb->s_root


Will adopt this in the next revision and add a selftest to check
this. Thanks for pointing this out!

>> > +}
>> > +
>> > +static int restrictedmem_create_on_user_mount(int mount_fd)
>> > +{
>> > +	int ret;
>> > +	struct fd f;
>> > +	struct vfsmount *mnt;
>> > +
>> > +	f = fdget_raw(mount_fd);
>> > +	if (!f.file)
>> > +		return -EBADF;
>> > +
>> > +	ret = -EINVAL;
>> > +	if (!is_mount_root(f.file))
>> > +		goto out;
>> > +
>> > +	mnt = f.file->f_path.mnt;
>> > +	if (!is_shmem_mount(mnt))
>> > +		goto out;
>> > +
>> > +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);

>> With the current semantics you're asking whether you have write
>> permissions on the /mnt/ble file in order to get answer to the question
>> whether you're allowed to create an unlinked restricted memory file.
>> That doesn't make much sense afaict.


That's true. Since mnt_want_write() already checks for write permissions
and this syscall creates an unlinked file on the mount, we don't have to
check permissions on the file then. Will remove this in the next
revision!

>> > +	if (ret)
>> > +		goto out;
>> > +
>> > +	ret = mnt_want_write(mnt);
>> > +	if (unlikely(ret))
>> > +		goto out;
>> > +
>> > +	ret = restrictedmem_create(mnt);
>> > +
>> > +	mnt_drop_write(mnt);
>> > +out:
>> > +	fdput(f);
>> > +
>> > +	return ret;
>> > +}
>> > +
>> > +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
>> > +{
>> > +	if (flags & ~RMFD_USERMNT)
>> > +		return -EINVAL;
>> > +
>> > +	if (flags == RMFD_USERMNT) {

>> Why do you even need this flag? It seems that @mount_fd being < 0 is
>> sufficient to indicate that a new restricted memory fd is supposed to be
>> created in the system instance.


I'm hoping to have this patch series merged after Chao's patch series
introduces the memfd_restricted() syscall [1].

This flag is necessary to indicate the validity of the second argument.

With this flag, we can definitively return an error if the fd is
invalid, which I think is a better experience for the userspace
programmer than if we just silently default to the kernel mount when the
fd provided is invalid.

>> > +		if (mount_fd < 0)
>> > +			return -EINVAL;
>> > +
>> > +		return restrictedmem_create_on_user_mount(mount_fd);
>> > +	} else {
>> > +		return restrictedmem_create(NULL);
>> > +	}
>> > +}

>> I have to say that I'm very confused by all of this the more I look at  
>> it.

>> Effectively memfd restricted functions as a wrapper filesystem around
>> the tmpfs filesystem. This is basically a weird overlay filesystem.
>> You're allocating tmpfs files that you stash in restrictedmem files.
>> I have to say that this seems very hacky. I didn't get this at all at
>> first.

>> So what does the caller get if they call statx() on a restricted memfd?
>> Do they get the device number of the tmpfs mount and the inode numbers
>> of the tmpfs mount? Because it looks like they would:

>> static int restrictedmem_getattr(struct user_namespace *mnt_userns,
>> 				 const struct path *path, struct kstat *stat,
>> 				 u32 request_mask, unsigned int query_flags)
>> {
>> 	struct inode *inode = d_inode(path->dentry);
>> 	struct restrictedmem *rm = inode->i_mapping->private_data;
>> 	struct file *memfd = rm->memfd;

>> 	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,

> This is pretty broken btw, because @path refers to a restrictedmem path
> which you're passing to a tmpfs iop...

> I see that in

> 	return memfd->f_inode->i_op->getattr(mnt_userns, &memfd->f_path, stat,
> 					     request_mask, query_flags);

> this if fixed but still, this is... not great.


Thanks, this will be fixed in the next revision by rebasing on Chao's
latest code.

>> 					     request_mask, query_flags);

>> That @memfd would be a struct file allocated in a tmpfs instance, no? So
>> you'd be calling the inode operation of the tmpfs file meaning that
>> struct kstat will be filled up with the info from the tmpfs instance.

>> But then if I call statfs() and check the fstype I would get
>> RESTRICTEDMEM_MAGIC, no? This is... unorthodox?

>> I'm honestly puzzled and this sounds really strange. There must be a
>> better way to implement all of this.

>> Shouldn't you try and make this a part of tmpfs proper? Make a really
>> separate filesystem and add a memfs library that both tmpfs and
>> restrictedmemfs can use? Add a mount option to tmpfs that makes it a
>> restricted tmpfs?

This was discussed earlier in the patch series introducing
memfd_restricted and this approach was taken to better manage ownership
of required functionalities between two subsystems. Please see
discussion beginning [2]

[1] ->  
https://lore.kernel.org/lkml/20221202061347.1070246-1-chao.p.peng@linux.intel.com/T/.
[2] ->  
https://lore.kernel.org/lkml/ff5c5b97-acdf-9745-ebe5-c6609dd6322e@google.com/

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Ackerley Tng]

Thanks for your review!

David Hildenbrand <david@redhat.com> writes:

> On 01.04.23 01:50, Ackerley Tng wrote:

>> ...

>> diff --git a/include/uapi/linux/restrictedmem.h  
>> b/include/uapi/linux/restrictedmem.h
>> new file mode 100644
>> index 000000000000..22d6f2285f6d
>> --- /dev/null
>> +++ b/include/uapi/linux/restrictedmem.h
>> @@ -0,0 +1,8 @@
>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>> +#ifndef _UAPI_LINUX_RESTRICTEDMEM_H
>> +#define _UAPI_LINUX_RESTRICTEDMEM_H
>> +
>> +/* flags for memfd_restricted */
>> +#define RMFD_USERMNT		0x0001U

> I wonder if we can come up with a more expressive prefix than RMFD.
> Sounds more like "rm fd" ;) Maybe it should better match the
> "memfd_restricted" syscall name, like "MEMFD_RSTD_USERMNT".


RMFD did actually sound vulgar, I'm good with MEMFD_RSTD_USERMNT!

>> +
>> +#endif /* _UAPI_LINUX_RESTRICTEDMEM_H */
>> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
>> index c5d869d8c2d8..f7b62364a31a 100644
>> --- a/mm/restrictedmem.c
>> +++ b/mm/restrictedmem.c
>> @@ -1,11 +1,12 @@
>>    // SPDX-License-Identifier: GPL-2.0
>> -#include "linux/sbitmap.h"

> Looks like an unrelated change?


Will remove this in the next revision.

>> +#include <linux/namei.h>
>>    #include <linux/pagemap.h>
>>    #include <linux/pseudo_fs.h>
>>    #include <linux/shmem_fs.h>
>>    #include <linux/syscalls.h>
>>    #include <uapi/linux/falloc.h>
>>    #include <uapi/linux/magic.h>
>> +#include <uapi/linux/restrictedmem.h>
>>    #include <linux/restrictedmem.h>

>>    struct restrictedmem {
>> @@ -189,19 +190,20 @@ static struct file  
>> *restrictedmem_file_create(struct file *memfd)
>>    	return file;
>>    }

>> -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
>> +static int restrictedmem_create(struct vfsmount *mount)
>>    {
>>    	struct file *file, *restricted_file;
>>    	int fd, err;

>> -	if (flags)
>> -		return -EINVAL;
>> -
>>    	fd = get_unused_fd_flags(0);
>>    	if (fd < 0)
>>    		return fd;

>> -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
>> +	if (mount)
>> +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0,  
>> VM_NORESERVE);
>> +	else
>> +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
>> +
>>    	if (IS_ERR(file)) {
>>    		err = PTR_ERR(file);
>>    		goto err_fd;
>> @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int,  
>> flags)
>>    	return err;
>>    }

>> +static bool is_shmem_mount(struct vfsmount *mnt)
>> +{
>> +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;
>> +}
>> +
>> +static bool is_mount_root(struct file *file)
>> +{
>> +	return file->f_path.dentry == file->f_path.mnt->mnt_root;
>> +}

> I'd inline at least that function, pretty self-explaining.


Will inline this in the next revision.

>> +
>> +static int restrictedmem_create_on_user_mount(int mount_fd)
>> +{
>> +	int ret;
>> +	struct fd f;
>> +	struct vfsmount *mnt;
>> +
>> +	f = fdget_raw(mount_fd);
>> +	if (!f.file)
>> +		return -EBADF;
>> +
>> +	ret = -EINVAL;
>> +	if (!is_mount_root(f.file))
>> +		goto out;
>> +
>> +	mnt = f.file->f_path.mnt;
>> +	if (!is_shmem_mount(mnt))
>> +		goto out;
>> +
>> +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = mnt_want_write(mnt);
>> +	if (unlikely(ret))
>> +		goto out;
>> +
>> +	ret = restrictedmem_create(mnt);
>> +
>> +	mnt_drop_write(mnt);
>> +out:
>> +	fdput(f);
>> +
>> +	return ret;
>> +}
>> +
>> +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
>> +{
>> +	if (flags & ~RMFD_USERMNT)
>> +		return -EINVAL;
>> +
>> +	if (flags == RMFD_USERMNT) {
>> +		if (mount_fd < 0)
>> +			return -EINVAL;
>> +
>> +		return restrictedmem_create_on_user_mount(mount_fd);
>> +	} else {
>> +		return restrictedmem_create(NULL);
>> +	}


> You can drop the else case:

> if (flags == RMFD_USERMNT) {
> 	...
> 	return restrictedmem_create_on_user_mount(mount_fd);
> }
> return restrictedmem_create(NULL);


I'll be refactoring this to adopt Kirill's suggestion of using a single
restrictedmem_create(mnt) call.


> I do wonder if you want to properly check for a flag instead of
> comparing values. Results in a more natural way to deal with flags:

> if (flags & RMFD_USERMNT) {

> }


Will use this in the next revision.

>> +}
>> +
>>    int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
>>    		       struct restrictedmem_notifier *notifier, bool exclusive)
>>    {

> The "memfd_restricted" vs. "restrictedmem" terminology is a bit
> unfortunate, but not your fault here.


> I'm not a FS person, but it does look good to me.

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Ackerley Tng]

Thanks for reviewing these patches!

"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Fri, Mar 31, 2023 at 11:50:39PM +0000, Ackerley Tng wrote:

>> ...

>> +static int restrictedmem_create_on_user_mount(int mount_fd)
>> +{
>> +	int ret;
>> +	struct fd f;
>> +	struct vfsmount *mnt;
>> +
>> +	f = fdget_raw(mount_fd);
>> +	if (!f.file)
>> +		return -EBADF;
>> +
>> +	ret = -EINVAL;
>> +	if (!is_mount_root(f.file))
>> +		goto out;
>> +
>> +	mnt = f.file->f_path.mnt;
>> +	if (!is_shmem_mount(mnt))
>> +		goto out;
>> +
>> +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);

> Why MAY_EXEC?


Christian pointed out that this check does not make sense, I'll be
removing the entire check in the next revision.

>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = mnt_want_write(mnt);
>> +	if (unlikely(ret))
>> +		goto out;
>> +
>> +	ret = restrictedmem_create(mnt);
>> +
>> +	mnt_drop_write(mnt);
>> +out:
>> +	fdput(f);
>> +
>> +	return ret;
>> +}

> We need review from fs folks. Look mostly sensible, but I have no
> experience in fs.

>> +
>> +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
>> +{
>> +	if (flags & ~RMFD_USERMNT)
>> +		return -EINVAL;
>> +
>> +	if (flags == RMFD_USERMNT) {
>> +		if (mount_fd < 0)
>> +			return -EINVAL;
>> +
>> +		return restrictedmem_create_on_user_mount(mount_fd);
>> +	} else {
>> +		return restrictedmem_create(NULL);
>> +	}

> Maybe restructure with single restrictedmem_create() call?

> 	struct vfsmount *mnt = NULL;

> 	if (flags == RMFD_USERMNT) {
> 		...
> 		mnt = ...();
> 	}

> 	return restrictedmem_create(mnt);

Will do so in the next revision.

>> +}
>> +
>>   int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
>>   		       struct restrictedmem_notifier *notifier, bool exclusive)
>>   {
>> --
>> 2.40.0.348.gf938b09366-goog

Re: [RFC PATCH v3 2/2] selftests: restrictedmem: Check hugepage-ness of shmem file backing restrictedmem fd

[Ackerley Tng]

David Hildenbrand <david@redhat.com> writes:

> On 01.04.23 01:50, Ackerley Tng wrote:
>> For memfd_restricted() calls without a userspace mount, the backing
>> file should be the shmem mount in the kernel, and the size of backing
>> pages should be as defined by system-wide shmem configuration.

>> If a userspace mount is provided, the size of backing pages should be
>> as defined in the mount.

>> Also includes negative tests for invalid inputs, including fds
>> representing read-only superblocks/mounts.


> When you talk about "hugepage" in this patch, do you mean THP or
> hugetlb? I suspect thp, so it might be better to spell that out. IIRC,
> there are plans to support actual huge pages in the future, at which
> point "hugepage" terminology could be misleading.


Thanks for pointing this out! I've replaced references to hugepage with
thp, please see RFC v4 at
https://lore.kernel.org/lkml/cover.1681176340.git.ackerleytng@google.com/T/

>> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
>> ---
>>    tools/testing/selftests/Makefile              |   1 +
>>    .../selftests/restrictedmem/.gitignore        |   3 +
>>    .../testing/selftests/restrictedmem/Makefile  |  15 +
>>    .../testing/selftests/restrictedmem/common.c  |   9 +
>>    .../testing/selftests/restrictedmem/common.h  |   8 +
>>    .../restrictedmem_hugepage_test.c             | 486 ++++++++++++++++++
>>    6 files changed, 522 insertions(+)
>>    create mode 100644 tools/testing/selftests/restrictedmem/.gitignore
>>    create mode 100644 tools/testing/selftests/restrictedmem/Makefile
>>    create mode 100644 tools/testing/selftests/restrictedmem/common.c
>>    create mode 100644 tools/testing/selftests/restrictedmem/common.h
>>    create mode 100644  
>> tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c

>> ...

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Christian Brauner]

On Wed, Apr 05, 2023 at 09:58:44PM +0000, Ackerley Tng wrote:
> 
> Thanks again for your review!
> 
> Christian Brauner <brauner@kernel.org> writes:
> > On Tue, Apr 04, 2023 at 03:53:13PM +0200, Christian Brauner wrote:
> > > On Fri, Mar 31, 2023 at 11:50:39PM +0000, Ackerley Tng wrote:
> > > >
> > > > ...
> > > >
> > > > -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> > > > +static int restrictedmem_create(struct vfsmount *mount)
> > > >  {
> > > >  	struct file *file, *restricted_file;
> > > >  	int fd, err;
> > > >
> > > > -	if (flags)
> > > > -		return -EINVAL;
> > > > -
> > > >  	fd = get_unused_fd_flags(0);
> 
> > > Any reasons the file descriptors aren't O_CLOEXEC by default? I don't
> > > see any reasons why we should introduce new fdtypes that aren't
> > > O_CLOEXEC by default. The "don't mix-and-match" train has already left
> > > the station anyway as we do have seccomp noitifer fds and pidfds both of
> > > which are O_CLOEXEC by default.
> 
> 
> Thanks for pointing this out. I agree with using O_CLOEXEC, but didn’t
> notice this before. Let us discuss this under the original series at
> [1].
> 
> > > >  	if (fd < 0)
> > > >  		return fd;
> > > >
> > > > -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> > > > +	if (mount)
> > > > +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem",
> > > 0, VM_NORESERVE);
> > > > +	else
> > > > +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> > > > +
> > > >  	if (IS_ERR(file)) {
> > > >  		err = PTR_ERR(file);
> > > >  		goto err_fd;
> > > > @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned
> > > int, flags)
> > > >  	return err;
> > > >  }
> > > >
> > > > +static bool is_shmem_mount(struct vfsmount *mnt)
> > > > +{
> > > > +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;
> 
> > > This can just be if (mnt->mnt_sb->s_magic == TMPFS_MAGIC).
> 
> 
> Will simplify this in the next revision.
> 
> > > > +}
> > > > +
> > > > +static bool is_mount_root(struct file *file)
> > > > +{
> > > > +	return file->f_path.dentry == file->f_path.mnt->mnt_root;
> 
> > > mount -t tmpfs tmpfs /mnt
> > > touch /mnt/bla
> > > touch /mnt/ble
> > > mount --bind /mnt/bla /mnt/ble
> > > fd = open("/mnt/ble")
> > > fd_restricted = memfd_restricted(fd)
> 
> > > IOW, this doesn't restrict it to the tmpfs root. It only restricts it to
> > > paths that refer to the root of any tmpfs mount. To exclude bind-mounts
> > > that aren't bind-mounts of the whole filesystem you want:
> 
> > > path->dentry == path->mnt->mnt_root &&
> > > path->mnt->mnt_root == path->mnt->mnt_sb->s_root
> 
> 
> Will adopt this in the next revision and add a selftest to check
> this. Thanks for pointing this out!
> 
> > > > +}
> > > > +
> > > > +static int restrictedmem_create_on_user_mount(int mount_fd)
> > > > +{
> > > > +	int ret;
> > > > +	struct fd f;
> > > > +	struct vfsmount *mnt;
> > > > +
> > > > +	f = fdget_raw(mount_fd);
> > > > +	if (!f.file)
> > > > +		return -EBADF;
> > > > +
> > > > +	ret = -EINVAL;
> > > > +	if (!is_mount_root(f.file))
> > > > +		goto out;
> > > > +
> > > > +	mnt = f.file->f_path.mnt;
> > > > +	if (!is_shmem_mount(mnt))
> > > > +		goto out;
> > > > +
> > > > +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);
> 
> > > With the current semantics you're asking whether you have write
> > > permissions on the /mnt/ble file in order to get answer to the question
> > > whether you're allowed to create an unlinked restricted memory file.
> > > That doesn't make much sense afaict.
> 
> 
> That's true. Since mnt_want_write() already checks for write permissions
> and this syscall creates an unlinked file on the mount, we don't have to
> check permissions on the file then. Will remove this in the next
> revision!
> 
> > > > +	if (ret)
> > > > +		goto out;
> > > > +
> > > > +	ret = mnt_want_write(mnt);
> > > > +	if (unlikely(ret))
> > > > +		goto out;
> > > > +
> > > > +	ret = restrictedmem_create(mnt);
> > > > +
> > > > +	mnt_drop_write(mnt);
> > > > +out:
> > > > +	fdput(f);
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
> > > > +{
> > > > +	if (flags & ~RMFD_USERMNT)
> > > > +		return -EINVAL;
> > > > +
> > > > +	if (flags == RMFD_USERMNT) {
> 
> > > Why do you even need this flag? It seems that @mount_fd being < 0 is
> > > sufficient to indicate that a new restricted memory fd is supposed to be
> > > created in the system instance.
> 
> 
> I'm hoping to have this patch series merged after Chao's patch series
> introduces the memfd_restricted() syscall [1].

I'm curious, is there an LSFMM session for this?

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Wed, Mar 22, 2023, Michael Roth wrote:
> On Tue, Feb 21, 2023 at 08:11:35PM +0800, Chao Peng wrote:
> > >   *fixup (upm_base_support): KVM: use inclusive ranges for restrictedmem binding/unbinding
> > >   *fixup (upm_base_support): mm: restrictedmem: use inclusive ranges for issuing invalidations
> > 
> > As many kernel APIs treat 'end' as exclusive, I would rather keep using
> > exclusive 'end' for these APIs(restrictedmem_bind/restrictedmem_unbind
> > and notifier callbacks) but fix it internally in the restrictedmem. E.g.
> > all the places where xarray API needs a 'last'/'max' we use 'end - 1'.
> > See below for the change.
> 
> Yes I did feel like I was fighting the kernel a bit on that; your
> suggestion seems like it would be a better fit.

Comically belated +1, XArray is the odd one here.

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Wed, Jan 25, 2023, Kirill A. Shutemov wrote:
> On Wed, Jan 25, 2023 at 12:20:26AM +0000, Sean Christopherson wrote:
> > On Tue, Jan 24, 2023, Liam Merwick wrote:
> > > On 14/01/2023 00:37, Sean Christopherson wrote:
> > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > This patch series implements KVM guest private memory for confidential
> > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > > TDX-protected guest memory, machine check can happen which can further
> > > > > crash the running host system, this is terrible for multi-tenant
> > > > > configurations. The host accesses include those from KVM userspace like
> > > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > > via a fd-based approach, but it can never access the guest memory
> > > > > content.
> > > > > 
> > > > > The patch series touches both core mm and KVM code. I appreciate
> > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > > reviews are always welcome.
> > > > >    - 01: mm change, target for mm tree
> > > > >    - 02-09: KVM change, target for KVM tree
> > > > 
> > > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > > is available here:
> > > > 
> > > >    git@github.com:sean-jc/linux.git x86/upm_base_support
> > > > 
> > > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > > a WIP.
> > > > 
> > > 
> > > When running LTP (https://github.com/linux-test-project/ltp) on the v10
> > > bits (and also with Sean's branch above) I encounter the following NULL
> > > pointer dereference with testcases/kernel/syscalls/madvise/madvise01
> > > (100% reproducible).
> > > 
> > > It appears that in restrictedmem_error_page()
> > > inode->i_mapping->private_data is NULL in the
> > > list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) but I
> > > don't know why.
> > 
> > Kirill, can you take a look?  Or pass the buck to someone who can? :-)
> 
> The patch below should help.
> 
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index 15c52301eeb9..39ada985c7c0 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -307,14 +307,29 @@ void restrictedmem_error_page(struct page *page, struct address_space *mapping)
>  
>  	spin_lock(&sb->s_inode_list_lock);
>  	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> -		struct restrictedmem *rm = inode->i_mapping->private_data;
>  		struct restrictedmem_notifier *notifier;
> -		struct file *memfd = rm->memfd;
> +		struct restrictedmem *rm;
>  		unsigned long index;
> +		struct file *memfd;
>  
> -		if (memfd->f_mapping != mapping)
> +		if (atomic_read(&inode->i_count))

Kirill, should this be

		if (!atomic_read(&inode->i_count))
			continue;

i.e. skip unreferenced inodes, not skip referenced inodes?

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Christian Brauner]

On Thu, Aug 18, 2022 at 04:24:21PM +0300, Kirill A . Shutemov wrote:
> On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote:
> > On Wed, 6 Jul 2022, Chao Peng wrote:
> > > This is the v7 of this series which tries to implement the fd-based KVM
> > > guest private memory.
> > 
> > Here at last are my reluctant thoughts on this patchset.
> > 
> > fd-based approach for supporting KVM guest private memory: fine.
> > 
> > Use or abuse of memfd and shmem.c: mistaken.
> > 
> > memfd_create() was an excellent way to put together the initial prototype.
> > 
> > But since then, TDX in particular has forced an effort into preventing
> > (by flags, seals, notifiers) almost everything that makes it shmem/tmpfs.
> > 
> > Are any of the shmem.c mods useful to existing users of shmem.c? No.
> > Is MFD_INACCESSIBLE useful or comprehensible to memfd_create() users? No.
> > 
> > What use do you have for a filesystem here?  Almost none.
> > IIUC, what you want is an fd through which QEMU can allocate kernel
> > memory, selectively free that memory, and communicate fd+offset+length
> > to KVM.  And perhaps an interface to initialize a little of that memory
> > from a template (presumably copied from a real file on disk somewhere).
> > 
> > You don't need shmem.c or a filesystem for that!
> > 
> > If your memory could be swapped, that would be enough of a good reason
> > to make use of shmem.c: but it cannot be swapped; and although there
> > are some references in the mailthreads to it perhaps being swappable
> > in future, I get the impression that will not happen soon if ever.
> > 
> > If your memory could be migrated, that would be some reason to use
> > filesystem page cache (because page migration happens to understand
> > that type of memory): but it cannot be migrated.
> 
> Migration support is in pipeline. It is part of TDX 1.5 [1]. And swapping
> theoretically possible, but I'm not aware of any plans as of now.
> 
> [1] https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html
> 
> > Some of these impressions may come from earlier iterations of the
> > patchset (v7 looks better in several ways than v5).  I am probably
> > underestimating the extent to which you have taken on board other
> > usages beyond TDX and SEV private memory, and rightly want to serve
> > them all with similar interfaces: perhaps there is enough justification
> > for shmem there, but I don't see it.  There was mention of userfaultfd
> > in one link: does that provide the justification for using shmem?
> > 
> > I'm afraid of the special demands you may make of memory allocation
> > later on - surprised that huge pages are not mentioned already;
> > gigantic contiguous extents? secretmem removed from direct map?
> 
> The design allows for extension to hugetlbfs if needed. Combination of
> MFD_INACCESSIBLE | MFD_HUGETLB should route this way. There should be zero
> implications for shmem. It is going to be separate struct memfile_backing_store.
> 
> I'm not sure secretmem is a fit here as we want to extend MFD_INACCESSIBLE
> to be movable if platform supports it and secretmem is not migratable by
> design (without direct mapping fragmentations).
> 
> > Here's what I would prefer, and imagine much easier for you to maintain;
> > but I'm no system designer, and may be misunderstanding throughout.
> > 
> > QEMU gets fd from opening /dev/kvm_something, uses ioctls (or perhaps
> > the fallocate syscall interface itself) to allocate and free the memory,
> > ioctl for initializing some of it too.  KVM in control of whether that
> > fd can be read or written or mmap'ed or whatever, no need to prevent it
> > in shmem.c, no need for flags, seals, notifications to and fro because
> > KVM is already in control and knows the history.  If shmem actually has
> > value, call into it underneath - somewhat like SysV SHM, and /dev/zero
> > mmap, and i915/gem make use of it underneath.  If shmem has nothing to
> > add, just allocate and free kernel memory directly, recorded in your
> > own xarray.
> 
> I guess shim layer on top of shmem *can* work. I don't see immediately why
> it would not. But I'm not sure it is right direction. We risk creating yet
> another parallel VM with own rules/locking/accounting that opaque to
> core-mm.

Sorry for necrobumping this thread but I've been reviewing the
memfd_restricted() extension that Ackerley is currently working on. I
was pointed to this thread as this is what the extension is building
on but I'll reply to both threads here.

From a glance at v10, memfd_restricted() is currently implemented as an
in-kernel stacking filesystem. A call to memfd_restricted() creates a
new restricted memfd file and a new unlinked tmpfs file and stashes the
tmpfs file into the memfd file's private data member. It then uses the
tmpfs file's f_ops and i_ops to perform the relevant file and inode
operations. So it has the same callstack as a general stacking
filesystem like overlayfs in some cases:

        memfd_restricted->getattr()
        -> tmpfs->getattr()
        
The extension that Ackerley is now proposing is to allow passing in a
tmpfs file descriptor explicitly to identify the tmpfs instance in which
to allocate the tmpfs file which is stashed in the memfd secret file.

So in the ->getattr() callstack I mentioned above this patchset
currently does:

        static int restrictedmem_getattr(struct user_namespace *mnt_userns,
                                        const struct path *path, struct kstat stat,
                                        u32 request_mask, unsigned int uery_flags)
        {
               struct inode *inode = d_inode(path->dentry);
               struct restrictedmem_data *data = node->i_mapping->private_data;
               struct file *memfd = data->memfd;
        
               return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
                                                    request_mask, query_flags);
        }

There's a bug in here that I mentioned in another thread and I see that
Ackerley has mentioned as well in
https://lore.kernel.org/lkml/diqzzga0fv96.fsf@ackerleytng-cloudtop-sg.c.googlers.com
namely that this is passing a restricted memfd struct path to a tmpfs
inode operation which is very wrong.

But also in the current implementation - I mentioned this in the other
thread as well - when you call stat() on a restricted memfd file
descriptor you get all the information about the underlying tmpfs inode.
Specifically this includes the device number and inode number.

But when you call statfs() then you get a report that this is a memfd
restricted filesystem which somehow shares the device number with a
tmpfs instance. That's messy.

Since you're effectively acting like a stacking filesystem you should
really use the device number of your memfd restricted filesystem. IOW,
sm like:

        stat->dev = memfd_restricted_dentry->d_sb->s_dev;

But then you run into trouble if you want to go forward with Ackerley's
extension that allows to explicitly pass in tmpfs fds to
memfd_restricted(). Afaict, two tmpfs instances might allocate the same
inode number. So now the inode and device number pair isn't unique
anymore.

So you might best be served by allocating and reporting your own inode
numbers as well.

But if you want to preserve the inode number and device number of the
relevant tmpfs instance but still report memfd restricted as your
filesystem type then I think it's reasonable to ask whether a stacking
implementation really makes sense here.

If you extend memfd_restricted() or even consider extending it in the
future to take tmpfs file descriptors as arguments to identify the tmpfs
instance in which to allocate the underlying tmpfs file for the new
restricted memfd file you should really consider a tmpfs based
implementation.

Because at that point it just feels like a pointless wrapper to get
custom f_ops and i_ops. Plus it's wasteful because you allocate dentries
and inodes that you don't really care about at all.

Just off the top of my hat you might be better served:
* by a new ioctl() on tmpfs instances that
  yield regular tmpfs file descriptors with restricted f_ops and i_ops.
  That's not that different from btrfs subvolumes which effectively are
  directories but are created through an ioctl().
* by a mount option to tmpfs that makes it act
  in this restricted manner then you don't need an ioctl() and can get
  away with regular open calls. Such a tmpfs instance would only create
  regular, restricted memfds.

I think especially with the possibility of an extension that allows you
to inherit tmpfs properties by allocating the memfd restriced file in a
specific tmpfs instance the argument that you're not really making use
of tmpfs things has gone out of the window.

> 
> Note that on machines that run TDX guests such memory would likely be the
> bulk of memory use. Treating it as a fringe case may bite us one day.
> 
> -- 
>   Kiryl Shutsemau / Kirill A. Shutemov

On Wed, Apr 05, 2023 at 09:58:44PM +0000, Ackerley Tng wrote:
> 
> Thanks again for your review!
> 
> Christian Brauner <brauner@kernel.org> writes:
> > On Tue, Apr 04, 2023 at 03:53:13PM +0200, Christian Brauner wrote:
> > > On Fri, Mar 31, 2023 at 11:50:39PM +0000, Ackerley Tng wrote:
> > > >
> > > > ...
> > > >
> > > > -SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> > > > +static int restrictedmem_create(struct vfsmount *mount)
> > > >  {
> > > >  	struct file *file, *restricted_file;
> > > >  	int fd, err;
> > > >
> > > > -	if (flags)
> > > > -		return -EINVAL;
> > > > -
> > > >  	fd = get_unused_fd_flags(0);
> 
> > > Any reasons the file descriptors aren't O_CLOEXEC by default? I don't
> > > see any reasons why we should introduce new fdtypes that aren't
> > > O_CLOEXEC by default. The "don't mix-and-match" train has already left
> > > the station anyway as we do have seccomp noitifer fds and pidfds both of
> > > which are O_CLOEXEC by default.
> 
> 
> Thanks for pointing this out. I agree with using O_CLOEXEC, but didn’t
> notice this before. Let us discuss this under the original series at
> [1].
> 
> > > >  	if (fd < 0)
> > > >  		return fd;
> > > >
> > > > -	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> > > > +	if (mount)
> > > > +		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem",
> > > 0, VM_NORESERVE);
> > > > +	else
> > > > +		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> > > > +
> > > >  	if (IS_ERR(file)) {
> > > >  		err = PTR_ERR(file);
> > > >  		goto err_fd;
> > > > @@ -223,6 +225,66 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned
> > > int, flags)
> > > >  	return err;
> > > >  }
> > > >
> > > > +static bool is_shmem_mount(struct vfsmount *mnt)
> > > > +{
> > > > +	return mnt && mnt->mnt_sb && mnt->mnt_sb->s_magic == TMPFS_MAGIC;
> 
> > > This can just be if (mnt->mnt_sb->s_magic == TMPFS_MAGIC).
> 
> 
> Will simplify this in the next revision.
> 
> > > > +}
> > > > +
> > > > +static bool is_mount_root(struct file *file)
> > > > +{
> > > > +	return file->f_path.dentry == file->f_path.mnt->mnt_root;
> 
> > > mount -t tmpfs tmpfs /mnt
> > > touch /mnt/bla
> > > touch /mnt/ble
> > > mount --bind /mnt/bla /mnt/ble
> > > fd = open("/mnt/ble")
> > > fd_restricted = memfd_restricted(fd)
> 
> > > IOW, this doesn't restrict it to the tmpfs root. It only restricts it to
> > > paths that refer to the root of any tmpfs mount. To exclude bind-mounts
> > > that aren't bind-mounts of the whole filesystem you want:
> 
> > > path->dentry == path->mnt->mnt_root &&
> > > path->mnt->mnt_root == path->mnt->mnt_sb->s_root
> 
> 
> Will adopt this in the next revision and add a selftest to check
> this. Thanks for pointing this out!
> 
> > > > +}
> > > > +
> > > > +static int restrictedmem_create_on_user_mount(int mount_fd)
> > > > +{
> > > > +	int ret;
> > > > +	struct fd f;
> > > > +	struct vfsmount *mnt;
> > > > +
> > > > +	f = fdget_raw(mount_fd);
> > > > +	if (!f.file)
> > > > +		return -EBADF;
> > > > +
> > > > +	ret = -EINVAL;
> > > > +	if (!is_mount_root(f.file))
> > > > +		goto out;
> > > > +
> > > > +	mnt = f.file->f_path.mnt;
> > > > +	if (!is_shmem_mount(mnt))
> > > > +		goto out;
> > > > +
> > > > +	ret = file_permission(f.file, MAY_WRITE | MAY_EXEC);
> 
> > > With the current semantics you're asking whether you have write
> > > permissions on the /mnt/ble file in order to get answer to the question
> > > whether you're allowed to create an unlinked restricted memory file.
> > > That doesn't make much sense afaict.
> 
> 
> That's true. Since mnt_want_write() already checks for write permissions
> and this syscall creates an unlinked file on the mount, we don't have to
> check permissions on the file then. Will remove this in the next
> revision!
> 
> > > > +	if (ret)
> > > > +		goto out;
> > > > +
> > > > +	ret = mnt_want_write(mnt);
> > > > +	if (unlikely(ret))
> > > > +		goto out;
> > > > +
> > > > +	ret = restrictedmem_create(mnt);
> > > > +
> > > > +	mnt_drop_write(mnt);
> > > > +out:
> > > > +	fdput(f);
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
> > > > +{
> > > > +	if (flags & ~RMFD_USERMNT)
> > > > +		return -EINVAL;
> > > > +
> > > > +	if (flags == RMFD_USERMNT) {
> 
> > > Why do you even need this flag? It seems that @mount_fd being < 0 is
> > > sufficient to indicate that a new restricted memory fd is supposed to be
> > > created in the system instance.
> 
> 
> I'm hoping to have this patch series merged after Chao's patch series
> introduces the memfd_restricted() syscall [1].
> 
> This flag is necessary to indicate the validity of the second argument.
> 
> With this flag, we can definitively return an error if the fd is
> invalid, which I think is a better experience for the userspace
> programmer than if we just silently default to the kernel mount when the
> fd provided is invalid.
> 
> > > > +		if (mount_fd < 0)
> > > > +			return -EINVAL;
> > > > +
> > > > +		return restrictedmem_create_on_user_mount(mount_fd);
> > > > +	} else {
> > > > +		return restrictedmem_create(NULL);
> > > > +	}
> > > > +}
> 
> > > I have to say that I'm very confused by all of this the more I look
> > > at it.
> 
> > > Effectively memfd restricted functions as a wrapper filesystem around
> > > the tmpfs filesystem. This is basically a weird overlay filesystem.
> > > You're allocating tmpfs files that you stash in restrictedmem files.
> > > I have to say that this seems very hacky. I didn't get this at all at
> > > first.
> 
> > > So what does the caller get if they call statx() on a restricted memfd?
> > > Do they get the device number of the tmpfs mount and the inode numbers
> > > of the tmpfs mount? Because it looks like they would:
> 
> > > static int restrictedmem_getattr(struct user_namespace *mnt_userns,
> > > 				 const struct path *path, struct kstat *stat,
> > > 				 u32 request_mask, unsigned int query_flags)
> > > {
> > > 	struct inode *inode = d_inode(path->dentry);
> > > 	struct restrictedmem *rm = inode->i_mapping->private_data;
> > > 	struct file *memfd = rm->memfd;
> 
> > > 	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> 
> > This is pretty broken btw, because @path refers to a restrictedmem path
> > which you're passing to a tmpfs iop...
> 
> > I see that in
> 
> > 	return memfd->f_inode->i_op->getattr(mnt_userns, &memfd->f_path, stat,
> > 					     request_mask, query_flags);
> 
> > this if fixed but still, this is... not great.
> 
> 
> Thanks, this will be fixed in the next revision by rebasing on Chao's
> latest code.
> 
> > > 					     request_mask, query_flags);
> 
> > > That @memfd would be a struct file allocated in a tmpfs instance, no? So
> > > you'd be calling the inode operation of the tmpfs file meaning that
> > > struct kstat will be filled up with the info from the tmpfs instance.
> 
> > > But then if I call statfs() and check the fstype I would get
> > > RESTRICTEDMEM_MAGIC, no? This is... unorthodox?
> 
> > > I'm honestly puzzled and this sounds really strange. There must be a
> > > better way to implement all of this.
> 
> > > Shouldn't you try and make this a part of tmpfs proper? Make a really
> > > separate filesystem and add a memfs library that both tmpfs and
> > > restrictedmemfs can use? Add a mount option to tmpfs that makes it a
> > > restricted tmpfs?
> 
> This was discussed earlier in the patch series introducing
> memfd_restricted and this approach was taken to better manage ownership
> of required functionalities between two subsystems. Please see
> discussion beginning [2]
> 
> [1] -> https://lore.kernel.org/lkml/20221202061347.1070246-1-chao.p.peng@linux.intel.com/T/.
> [2] ->
> https://lore.kernel.org/lkml/ff5c5b97-acdf-9745-ebe5-c6609dd6322e@google.com/

On Fri, Dec 02, 2022 at 02:13:39PM +0800, Chao Peng wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> 
> Introduce 'memfd_restricted' system call with the ability to create
> memory areas that are restricted from userspace access through ordinary
> MMU operations (e.g. read/write/mmap). The memory content is expected to
> be used through the new in-kernel interface by a third kernel module.
> 
> memfd_restricted() is useful for scenarios where a file descriptor(fd)
> can be used as an interface into mm but want to restrict userspace's
> ability on the fd. Initially it is designed to provide protections for
> KVM encrypted guest memory.
> 
> Normally KVM uses memfd memory via mmapping the memfd into KVM userspace
> (e.g. QEMU) and then using the mmaped virtual address to setup the
> mapping in the KVM secondary page table (e.g. EPT). With confidential
> computing technologies like Intel TDX, the memfd memory may be encrypted
> with special key for special software domain (e.g. KVM guest) and is not
> expected to be directly accessed by userspace. Precisely, userspace
> access to such encrypted memory may lead to host crash so should be
> prevented.
> 
> memfd_restricted() provides semantics required for KVM guest encrypted
> memory support that a fd created with memfd_restricted() is going to be
> used as the source of guest memory in confidential computing environment
> and KVM can directly interact with core-mm without the need to expose
> the memoy content into KVM userspace.
> 
> KVM userspace is still in charge of the lifecycle of the fd. It should
> pass the created fd to KVM. KVM uses the new restrictedmem_get_page() to
> obtain the physical memory page and then uses it to populate the KVM
> secondary page table entries.
> 
> The userspace restricted memfd can be fallocate-ed or hole-punched
> from userspace. When hole-punched, KVM can get notified through
> invalidate_start/invalidate_end() callbacks, KVM then gets chance to
> remove any mapped entries of the range in the secondary page tables.
> 
> Machine check can happen for memory pages in the restricted memfd,
> instead of routing this directly to userspace, we call the error()
> callback that KVM registered. KVM then gets chance to handle it
> correctly.
> 
> memfd_restricted() itself is implemented as a shim layer on top of real
> memory file systems (currently tmpfs). Pages in restrictedmem are marked
> as unmovable and unevictable, this is required for current confidential
> usage. But in future this might be changed.
> 
> By default memfd_restricted() prevents userspace read, write and mmap.
> By defining new bit in the 'flags', it can be extended to support other
> restricted semantics in the future.
> 
> The system call is currently wired up for x86 arch.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  arch/x86/entry/syscalls/syscall_32.tbl |   1 +
>  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
>  include/linux/restrictedmem.h          |  71 ++++++
>  include/linux/syscalls.h               |   1 +
>  include/uapi/asm-generic/unistd.h      |   5 +-
>  include/uapi/linux/magic.h             |   1 +
>  kernel/sys_ni.c                        |   3 +
>  mm/Kconfig                             |   4 +
>  mm/Makefile                            |   1 +
>  mm/memory-failure.c                    |   3 +
>  mm/restrictedmem.c                     | 318 +++++++++++++++++++++++++
>  11 files changed, 408 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/restrictedmem.h
>  create mode 100644 mm/restrictedmem.c
> 
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index 320480a8db4f..dc70ba90247e 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -455,3 +455,4 @@
>  448	i386	process_mrelease	sys_process_mrelease
>  449	i386	futex_waitv		sys_futex_waitv
>  450	i386	set_mempolicy_home_node		sys_set_mempolicy_home_node
> +451	i386	memfd_restricted	sys_memfd_restricted
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index c84d12608cd2..06516abc8318 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -372,6 +372,7 @@
>  448	common	process_mrelease	sys_process_mrelease
>  449	common	futex_waitv		sys_futex_waitv
>  450	common	set_mempolicy_home_node	sys_set_mempolicy_home_node
> +451	common	memfd_restricted	sys_memfd_restricted
>  
>  #
>  # Due to a historical design error, certain syscalls are numbered differently
> diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h
> new file mode 100644
> index 000000000000..c2700c5daa43
> --- /dev/null
> +++ b/include/linux/restrictedmem.h
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _LINUX_RESTRICTEDMEM_H
> +
> +#include <linux/file.h>
> +#include <linux/magic.h>
> +#include <linux/pfn_t.h>
> +
> +struct restrictedmem_notifier;
> +
> +struct restrictedmem_notifier_ops {
> +	void (*invalidate_start)(struct restrictedmem_notifier *notifier,
> +				 pgoff_t start, pgoff_t end);
> +	void (*invalidate_end)(struct restrictedmem_notifier *notifier,
> +			       pgoff_t start, pgoff_t end);
> +	void (*error)(struct restrictedmem_notifier *notifier,
> +			       pgoff_t start, pgoff_t end);
> +};
> +
> +struct restrictedmem_notifier {
> +	struct list_head list;
> +	const struct restrictedmem_notifier_ops *ops;
> +};
> +
> +#ifdef CONFIG_RESTRICTEDMEM
> +
> +void restrictedmem_register_notifier(struct file *file,
> +				     struct restrictedmem_notifier *notifier);
> +void restrictedmem_unregister_notifier(struct file *file,
> +				       struct restrictedmem_notifier *notifier);
> +
> +int restrictedmem_get_page(struct file *file, pgoff_t offset,
> +			   struct page **pagep, int *order);
> +
> +static inline bool file_is_restrictedmem(struct file *file)
> +{
> +	return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC;
> +}
> +
> +void restrictedmem_error_page(struct page *page, struct address_space *mapping);
> +
> +#else
> +
> +static inline void restrictedmem_register_notifier(struct file *file,
> +				     struct restrictedmem_notifier *notifier)
> +{
> +}
> +
> +static inline void restrictedmem_unregister_notifier(struct file *file,
> +				       struct restrictedmem_notifier *notifier)
> +{
> +}
> +
> +static inline int restrictedmem_get_page(struct file *file, pgoff_t offset,
> +					 struct page **pagep, int *order)
> +{
> +	return -1;
> +}
> +
> +static inline bool file_is_restrictedmem(struct file *file)
> +{
> +	return false;
> +}
> +
> +static inline void restrictedmem_error_page(struct page *page,
> +					    struct address_space *mapping)
> +{
> +}
> +
> +#endif /* CONFIG_RESTRICTEDMEM */
> +
> +#endif /* _LINUX_RESTRICTEDMEM_H */
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index a34b0f9a9972..f9e9e0c820c5 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1056,6 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
>  asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
>  					    unsigned long home_node,
>  					    unsigned long flags);
> +asmlinkage long sys_memfd_restricted(unsigned int flags);
>  
>  /*
>   * Architecture-specific system calls
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index 45fa180cc56a..e93cd35e46d0 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
>  #define __NR_set_mempolicy_home_node 450
>  __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
>  
> +#define __NR_memfd_restricted 451
> +__SYSCALL(__NR_memfd_restricted, sys_memfd_restricted)
> +
>  #undef __NR_syscalls
> -#define __NR_syscalls 451
> +#define __NR_syscalls 452
>  
>  /*
>   * 32 bit systems traditionally used different
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index 6325d1d0e90f..8aa38324b90a 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -101,5 +101,6 @@
>  #define DMA_BUF_MAGIC		0x444d4142	/* "DMAB" */
>  #define DEVMEM_MAGIC		0x454d444d	/* "DMEM" */
>  #define SECRETMEM_MAGIC		0x5345434d	/* "SECM" */
> +#define RESTRICTEDMEM_MAGIC	0x5245534d	/* "RESM" */
>  
>  #endif /* __LINUX_MAGIC_H__ */
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 860b2dcf3ac4..7c4a32cbd2e7 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -360,6 +360,9 @@ COND_SYSCALL(pkey_free);
>  /* memfd_secret */
>  COND_SYSCALL(memfd_secret);
>  
> +/* memfd_restricted */
> +COND_SYSCALL(memfd_restricted);
> +
>  /*
>   * Architecture specific weak syscall entries.
>   */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 57e1d8c5b505..06b0e1d6b8c1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1076,6 +1076,10 @@ config IO_MAPPING
>  config SECRETMEM
>  	def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
>  
> +config RESTRICTEDMEM
> +	bool
> +	depends on TMPFS
> +
>  config ANON_VMA_NAME
>  	bool "Anonymous VMA name support"
>  	depends on PROC_FS && ADVISE_SYSCALLS && MMU
> diff --git a/mm/Makefile b/mm/Makefile
> index 8e105e5b3e29..bcbb0edf9ba1 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -121,6 +121,7 @@ obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
>  obj-$(CONFIG_PAGE_TABLE_CHECK) += page_table_check.o
>  obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
>  obj-$(CONFIG_SECRETMEM) += secretmem.o
> +obj-$(CONFIG_RESTRICTEDMEM) += restrictedmem.o
>  obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o
>  obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
>  obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 145bb561ddb3..f91b444e471e 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -62,6 +62,7 @@
>  #include <linux/page-isolation.h>
>  #include <linux/pagewalk.h>
>  #include <linux/shmem_fs.h>
> +#include <linux/restrictedmem.h>
>  #include "swap.h"
>  #include "internal.h"
>  #include "ras/ras_event.h"
> @@ -940,6 +941,8 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
>  		goto out;
>  	}
>  
> +	restrictedmem_error_page(p, mapping);
> +
>  	/*
>  	 * The shmem page is kept in page cache instead of truncating
>  	 * so is expected to have an extra refcount after error-handling.
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> new file mode 100644
> index 000000000000..56953c204e5c
> --- /dev/null
> +++ b/mm/restrictedmem.c
> @@ -0,0 +1,318 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "linux/sbitmap.h"
> +#include <linux/pagemap.h>
> +#include <linux/pseudo_fs.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/syscalls.h>
> +#include <uapi/linux/falloc.h>
> +#include <uapi/linux/magic.h>
> +#include <linux/restrictedmem.h>
> +
> +struct restrictedmem_data {
> +	struct mutex lock;
> +	struct file *memfd;
> +	struct list_head notifiers;
> +};
> +
> +static void restrictedmem_invalidate_start(struct restrictedmem_data *data,
> +					   pgoff_t start, pgoff_t end)
> +{
> +	struct restrictedmem_notifier *notifier;
> +
> +	mutex_lock(&data->lock);
> +	list_for_each_entry(notifier, &data->notifiers, list) {
> +		notifier->ops->invalidate_start(notifier, start, end);
> +	}
> +	mutex_unlock(&data->lock);
> +}
> +
> +static void restrictedmem_invalidate_end(struct restrictedmem_data *data,
> +					 pgoff_t start, pgoff_t end)
> +{
> +	struct restrictedmem_notifier *notifier;
> +
> +	mutex_lock(&data->lock);
> +	list_for_each_entry(notifier, &data->notifiers, list) {
> +		notifier->ops->invalidate_end(notifier, start, end);
> +	}
> +	mutex_unlock(&data->lock);
> +}
> +
> +static void restrictedmem_notifier_error(struct restrictedmem_data *data,
> +					 pgoff_t start, pgoff_t end)
> +{
> +	struct restrictedmem_notifier *notifier;
> +
> +	mutex_lock(&data->lock);
> +	list_for_each_entry(notifier, &data->notifiers, list) {
> +		notifier->ops->error(notifier, start, end);
> +	}
> +	mutex_unlock(&data->lock);
> +}
> +
> +static int restrictedmem_release(struct inode *inode, struct file *file)
> +{
> +	struct restrictedmem_data *data = inode->i_mapping->private_data;
> +
> +	fput(data->memfd);
> +	kfree(data);
> +	return 0;
> +}
> +
> +static long restrictedmem_punch_hole(struct restrictedmem_data *data, int mode,
> +				     loff_t offset, loff_t len)
> +{
> +	int ret;
> +	pgoff_t start, end;
> +	struct file *memfd = data->memfd;
> +
> +	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> +		return -EINVAL;
> +
> +	start = offset >> PAGE_SHIFT;
> +	end = (offset + len) >> PAGE_SHIFT;
> +
> +	restrictedmem_invalidate_start(data, start, end);
> +	ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> +	restrictedmem_invalidate_end(data, start, end);
> +
> +	return ret;
> +}
> +
> +static long restrictedmem_fallocate(struct file *file, int mode,
> +				    loff_t offset, loff_t len)
> +{
> +	struct restrictedmem_data *data = file->f_mapping->private_data;
> +	struct file *memfd = data->memfd;
> +
> +	if (mode & FALLOC_FL_PUNCH_HOLE)
> +		return restrictedmem_punch_hole(data, mode, offset, len);
> +
> +	return memfd->f_op->fallocate(memfd, mode, offset, len);
> +}
> +
> +static const struct file_operations restrictedmem_fops = {
> +	.release = restrictedmem_release,
> +	.fallocate = restrictedmem_fallocate,
> +};
> +
> +static int restrictedmem_getattr(struct user_namespace *mnt_userns,
> +				 const struct path *path, struct kstat *stat,
> +				 u32 request_mask, unsigned int query_flags)
> +{
> +	struct inode *inode = d_inode(path->dentry);
> +	struct restrictedmem_data *data = inode->i_mapping->private_data;
> +	struct file *memfd = data->memfd;
> +
> +	return memfd->f_inode->i_op->getattr(mnt_userns, path, stat,
> +					     request_mask, query_flags);
> +}
> +
> +static int restrictedmem_setattr(struct user_namespace *mnt_userns,
> +				 struct dentry *dentry, struct iattr *attr)
> +{
> +	struct inode *inode = d_inode(dentry);
> +	struct restrictedmem_data *data = inode->i_mapping->private_data;
> +	struct file *memfd = data->memfd;
> +	int ret;
> +
> +	if (attr->ia_valid & ATTR_SIZE) {
> +		if (memfd->f_inode->i_size)
> +			return -EPERM;
> +
> +		if (!PAGE_ALIGNED(attr->ia_size))
> +			return -EINVAL;
> +	}
> +
> +	ret = memfd->f_inode->i_op->setattr(mnt_userns,
> +					    file_dentry(memfd), attr);
> +	return ret;
> +}
> +
> +static const struct inode_operations restrictedmem_iops = {
> +	.getattr = restrictedmem_getattr,
> +	.setattr = restrictedmem_setattr,
> +};
> +
> +static int restrictedmem_init_fs_context(struct fs_context *fc)
> +{
> +	if (!init_pseudo(fc, RESTRICTEDMEM_MAGIC))
> +		return -ENOMEM;
> +
> +	fc->s_iflags |= SB_I_NOEXEC;
> +	return 0;
> +}
> +
> +static struct file_system_type restrictedmem_fs = {
> +	.owner		= THIS_MODULE,
> +	.name		= "memfd:restrictedmem",
> +	.init_fs_context = restrictedmem_init_fs_context,
> +	.kill_sb	= kill_anon_super,
> +};
> +
> +static struct vfsmount *restrictedmem_mnt;
> +
> +static __init int restrictedmem_init(void)
> +{
> +	restrictedmem_mnt = kern_mount(&restrictedmem_fs);
> +	if (IS_ERR(restrictedmem_mnt))
> +		return PTR_ERR(restrictedmem_mnt);
> +	return 0;
> +}
> +fs_initcall(restrictedmem_init);
> +
> +static struct file *restrictedmem_file_create(struct file *memfd)
> +{
> +	struct restrictedmem_data *data;
> +	struct address_space *mapping;
> +	struct inode *inode;
> +	struct file *file;
> +
> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return ERR_PTR(-ENOMEM);
> +
> +	data->memfd = memfd;
> +	mutex_init(&data->lock);
> +	INIT_LIST_HEAD(&data->notifiers);
> +
> +	inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
> +	if (IS_ERR(inode)) {
> +		kfree(data);
> +		return ERR_CAST(inode);
> +	}
> +
> +	inode->i_mode |= S_IFREG;
> +	inode->i_op = &restrictedmem_iops;
> +	inode->i_mapping->private_data = data;
> +
> +	file = alloc_file_pseudo(inode, restrictedmem_mnt,
> +				 "restrictedmem", O_RDWR,
> +				 &restrictedmem_fops);
> +	if (IS_ERR(file)) {
> +		iput(inode);
> +		kfree(data);
> +		return ERR_CAST(file);
> +	}
> +
> +	file->f_flags |= O_LARGEFILE;
> +
> +	/*
> +	 * These pages are currently unmovable so don't place them into movable
> +	 * pageblocks (e.g. CMA and ZONE_MOVABLE).
> +	 */
> +	mapping = memfd->f_mapping;
> +	mapping_set_unevictable(mapping);
> +	mapping_set_gfp_mask(mapping,
> +			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> +
> +	return file;
> +}
> +
> +SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
> +{
> +	struct file *file, *restricted_file;
> +	int fd, err;
> +
> +	if (flags)
> +		return -EINVAL;
> +
> +	fd = get_unused_fd_flags(0);
> +	if (fd < 0)
> +		return fd;
> +
> +	file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
> +	if (IS_ERR(file)) {
> +		err = PTR_ERR(file);
> +		goto err_fd;
> +	}
> +	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
> +	file->f_flags |= O_LARGEFILE;
> +
> +	restricted_file = restrictedmem_file_create(file);
> +	if (IS_ERR(restricted_file)) {
> +		err = PTR_ERR(restricted_file);
> +		fput(file);
> +		goto err_fd;
> +	}
> +
> +	fd_install(fd, restricted_file);
> +	return fd;
> +err_fd:
> +	put_unused_fd(fd);
> +	return err;
> +}
> +
> +void restrictedmem_register_notifier(struct file *file,
> +				     struct restrictedmem_notifier *notifier)
> +{
> +	struct restrictedmem_data *data = file->f_mapping->private_data;
> +
> +	mutex_lock(&data->lock);
> +	list_add(&notifier->list, &data->notifiers);
> +	mutex_unlock(&data->lock);
> +}
> +EXPORT_SYMBOL_GPL(restrictedmem_register_notifier);
> +
> +void restrictedmem_unregister_notifier(struct file *file,
> +				       struct restrictedmem_notifier *notifier)
> +{
> +	struct restrictedmem_data *data = file->f_mapping->private_data;
> +
> +	mutex_lock(&data->lock);
> +	list_del(&notifier->list);
> +	mutex_unlock(&data->lock);
> +}
> +EXPORT_SYMBOL_GPL(restrictedmem_unregister_notifier);
> +
> +int restrictedmem_get_page(struct file *file, pgoff_t offset,
> +			   struct page **pagep, int *order)
> +{
> +	struct restrictedmem_data *data = file->f_mapping->private_data;
> +	struct file *memfd = data->memfd;
> +	struct folio *folio;
> +	struct page *page;
> +	int ret;
> +
> +	ret = shmem_get_folio(file_inode(memfd), offset, &folio, SGP_WRITE);
> +	if (ret)
> +		return ret;
> +
> +	page = folio_file_page(folio, offset);
> +	*pagep = page;
> +	if (order)
> +		*order = thp_order(compound_head(page));
> +
> +	SetPageUptodate(page);
> +	unlock_page(page);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(restrictedmem_get_page);
> +
> +void restrictedmem_error_page(struct page *page, struct address_space *mapping)
> +{
> +	struct super_block *sb = restrictedmem_mnt->mnt_sb;
> +	struct inode *inode, *next;
> +
> +	if (!shmem_mapping(mapping))
> +		return;
> +
> +	spin_lock(&sb->s_inode_list_lock);
> +	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> +		struct restrictedmem_data *data = inode->i_mapping->private_data;
> +		struct file *memfd = data->memfd;
> +
> +		if (memfd->f_mapping == mapping) {
> +			pgoff_t start, end;
> +
> +			spin_unlock(&sb->s_inode_list_lock);
> +
> +			start = page->index;
> +			end = start + thp_nr_pages(page);
> +			restrictedmem_notifier_error(data, start, end);
> +			return;
> +		}
> +	}
> +	spin_unlock(&sb->s_inode_list_lock);
> +}
> -- 
> 2.25.1
> 

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Kirill A. Shutemov]

On Wed, Apr 12, 2023 at 06:07:28PM -0700, Sean Christopherson wrote:
> On Wed, Jan 25, 2023, Kirill A. Shutemov wrote:
> > On Wed, Jan 25, 2023 at 12:20:26AM +0000, Sean Christopherson wrote:
> > > On Tue, Jan 24, 2023, Liam Merwick wrote:
> > > > On 14/01/2023 00:37, Sean Christopherson wrote:
> > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > > This patch series implements KVM guest private memory for confidential
> > > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > > > TDX-protected guest memory, machine check can happen which can further
> > > > > > crash the running host system, this is terrible for multi-tenant
> > > > > > configurations. The host accesses include those from KVM userspace like
> > > > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > > > via a fd-based approach, but it can never access the guest memory
> > > > > > content.
> > > > > > 
> > > > > > The patch series touches both core mm and KVM code. I appreciate
> > > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > > > reviews are always welcome.
> > > > > >    - 01: mm change, target for mm tree
> > > > > >    - 02-09: KVM change, target for KVM tree
> > > > > 
> > > > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > > > is available here:
> > > > > 
> > > > >    git@github.com:sean-jc/linux.git x86/upm_base_support
> > > > > 
> > > > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > > > a WIP.
> > > > > 
> > > > 
> > > > When running LTP (https://github.com/linux-test-project/ltp) on the v10
> > > > bits (and also with Sean's branch above) I encounter the following NULL
> > > > pointer dereference with testcases/kernel/syscalls/madvise/madvise01
> > > > (100% reproducible).
> > > > 
> > > > It appears that in restrictedmem_error_page()
> > > > inode->i_mapping->private_data is NULL in the
> > > > list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) but I
> > > > don't know why.
> > > 
> > > Kirill, can you take a look?  Or pass the buck to someone who can? :-)
> > 
> > The patch below should help.
> > 
> > diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> > index 15c52301eeb9..39ada985c7c0 100644
> > --- a/mm/restrictedmem.c
> > +++ b/mm/restrictedmem.c
> > @@ -307,14 +307,29 @@ void restrictedmem_error_page(struct page *page, struct address_space *mapping)
> >  
> >  	spin_lock(&sb->s_inode_list_lock);
> >  	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> > -		struct restrictedmem *rm = inode->i_mapping->private_data;
> >  		struct restrictedmem_notifier *notifier;
> > -		struct file *memfd = rm->memfd;
> > +		struct restrictedmem *rm;
> >  		unsigned long index;
> > +		struct file *memfd;
> >  
> > -		if (memfd->f_mapping != mapping)
> > +		if (atomic_read(&inode->i_count))
> 
> Kirill, should this be
> 
> 		if (!atomic_read(&inode->i_count))
> 			continue;
> 
> i.e. skip unreferenced inodes, not skip referenced inodes?

Ouch. Yes.

But looking at other instances of s_inodes usage, I think we can drop the
check altogether. inode cannot be completely free until it is removed from
s_inodes list.

While there, replace list_for_each_entry_safe() with
list_for_each_entry() as we don't remove anything from the list.

diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
index 55e99e6c09a1..8e8a4420d3d1 100644
--- a/mm/restrictedmem.c
+++ b/mm/restrictedmem.c
@@ -194,22 +194,19 @@ static int restricted_error_remove_page(struct address_space *mapping,
 					struct page *page)
 {
 	struct super_block *sb = restrictedmem_mnt->mnt_sb;
-	struct inode *inode, *next;
+	struct inode *inode;
 	pgoff_t start, end;
 
 	start = page->index;
 	end = start + thp_nr_pages(page);
 
 	spin_lock(&sb->s_inode_list_lock);
-	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
+	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
 		struct restrictedmem_notifier *notifier;
 		struct restrictedmem *rm;
 		unsigned long index;
 		struct file *memfd;
 
-		if (atomic_read(&inode->i_count))
-			continue;
-
 		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
 			spin_unlock(&inode->i_lock);
-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

[Ackerley Tng]

Chao Peng <chao.p.peng@linux.intel.com> writes:

> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

> Introduce 'memfd_restricted' system call with the ability to create
> memory areas that are restricted from userspace access through ordinary
> MMU operations (e.g. read/write/mmap). The memory content is expected to
> be used through the new in-kernel interface by a third kernel module.

> ...

> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> new file mode 100644
> index 000000000000..56953c204e5c
> --- /dev/null
> +++ b/mm/restrictedmem.c
> @@ -0,0 +1,318 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "linux/sbitmap.h"
> +#include <linux/pagemap.h>
> +#include <linux/pseudo_fs.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/syscalls.h>
> +#include <uapi/linux/falloc.h>
> +#include <uapi/linux/magic.h>
> +#include <linux/restrictedmem.h>
> +
> +struct restrictedmem_data {
> +	struct mutex lock;
> +	struct file *memfd;

Can this be renamed to file, or lower_file (as in stacking filesystems)?

It's a little confusing because this pointer doesn't actually refer to
an fd.

'memfd' is already used by udmabuf to refer to an actual fd [1], which
makes this a little misleading.

[1]  
https://elixir.bootlin.com/linux/v6.2.10/source/tools/testing/selftests/drivers/dma-buf/udmabuf.c#L63

> +	struct list_head notifiers;
> +};
> +
> ...

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Sean Christopherson]

On Thu, Apr 13, 2023, Christian Brauner wrote:
> On Thu, Aug 18, 2022 at 04:24:21PM +0300, Kirill A . Shutemov wrote:
> > On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote:
> > > Here's what I would prefer, and imagine much easier for you to maintain;
> > > but I'm no system designer, and may be misunderstanding throughout.
> > > 
> > > QEMU gets fd from opening /dev/kvm_something, uses ioctls (or perhaps
> > > the fallocate syscall interface itself) to allocate and free the memory,
> > > ioctl for initializing some of it too.  KVM in control of whether that
> > > fd can be read or written or mmap'ed or whatever, no need to prevent it
> > > in shmem.c, no need for flags, seals, notifications to and fro because
> > > KVM is already in control and knows the history.  If shmem actually has
> > > value, call into it underneath - somewhat like SysV SHM, and /dev/zero
> > > mmap, and i915/gem make use of it underneath.  If shmem has nothing to
> > > add, just allocate and free kernel memory directly, recorded in your
> > > own xarray.
> > 
> > I guess shim layer on top of shmem *can* work. I don't see immediately why
> > it would not. But I'm not sure it is right direction. We risk creating yet
> > another parallel VM with own rules/locking/accounting that opaque to
> > core-mm.
> 
> Sorry for necrobumping this thread but I've been reviewing the

No worries, I'm just stoked someone who actually knows what they're doing is
chiming in :-)

> memfd_restricted() extension that Ackerley is currently working on. I
> was pointed to this thread as this is what the extension is building
> on but I'll reply to both threads here.
> 
> From a glance at v10, memfd_restricted() is currently implemented as an
> in-kernel stacking filesystem. A call to memfd_restricted() creates a
> new restricted memfd file and a new unlinked tmpfs file and stashes the
> tmpfs file into the memfd file's private data member. It then uses the
> tmpfs file's f_ops and i_ops to perform the relevant file and inode
> operations. So it has the same callstack as a general stacking
> filesystem like overlayfs in some cases:
> 
>         memfd_restricted->getattr()
>         -> tmpfs->getattr()

...

> Since you're effectively acting like a stacking filesystem you should
> really use the device number of your memfd restricted filesystem. IOW,
> sm like:
> 
>         stat->dev = memfd_restricted_dentry->d_sb->s_dev;
> 
> But then you run into trouble if you want to go forward with Ackerley's
> extension that allows to explicitly pass in tmpfs fds to
> memfd_restricted(). Afaict, two tmpfs instances might allocate the same
> inode number. So now the inode and device number pair isn't unique
> anymore.
> 
> So you might best be served by allocating and reporting your own inode
> numbers as well.
> 
> But if you want to preserve the inode number and device number of the
> relevant tmpfs instance but still report memfd restricted as your
> filesystem type

Unless I missed something along the way, reporting memfd_restricted as a distinct
filesystem is very much a non-goal.  AFAIK it's purely a side effect of the
proposed implementation.

> then I think it's reasonable to ask whether a stacking implementation really
> makes sense here.
> 
> If you extend memfd_restricted() or even consider extending it in the
> future to take tmpfs file descriptors as arguments to identify the tmpfs
> instance in which to allocate the underlying tmpfs file for the new
> restricted memfd file you should really consider a tmpfs based
> implementation.
> 
> Because at that point it just feels like a pointless wrapper to get
> custom f_ops and i_ops. Plus it's wasteful because you allocate dentries
> and inodes that you don't really care about at all.
> 
> Just off the top of my hat you might be better served:
> * by a new ioctl() on tmpfs instances that
>   yield regular tmpfs file descriptors with restricted f_ops and i_ops.
>   That's not that different from btrfs subvolumes which effectively are
>   directories but are created through an ioctl().

I think this is more or less what we want to do, except via a dedicated syscall
instead of an ioctl() so that the primary interface isn't strictly tied to tmpfs,
e.g. so that it can be extended to other backing types in the future.

> * by a mount option to tmpfs that makes it act
>   in this restricted manner then you don't need an ioctl() and can get
>   away with regular open calls. Such a tmpfs instance would only create
>   regular, restricted memfds.

I'd prefer to not go this route, becuase IIUC, it would require relatively invasive
changes to shmem code, and IIUC would require similar changes to other support
backings in the future, e.g. hugetlbfs?  And as above, I don't think any of the
potential use cases need restrictedmem to be a uniquely identifiable mount.

One of the goals (hopefully not a pipe dream) is to design restrictmem in such a
way that extending it to support other backing types isn't terribly difficult.
In case it's not obvious, most of us working on this stuff aren't filesystems
experts, and many of us aren't mm experts either.  The more we (KVM folks for the
most part) can leverage existing code to do the heavy lifting, the better.

After giving myself a bit of a crash course in file systems, would something like
the below have any chance of (a) working, (b) getting merged, and (c) being
maintainable?

The idea is similar to a stacking filesystem, but instead of stacking, restrictedmem
hijacks a f_ops and a_ops to create a lightweight shim around tmpfs.  There are
undoubtedly issues and edge cases, I'm just looking for a quick "yes, this might
be doable" or a "no, that's absolutely bonkers, don't try it".

Thanks!


struct restrictedmem {
	struct rw_semaphore lock;
	struct file *file;
	const struct file_operations *backing_f_ops;
	const struct address_space_operations *backing_a_ops;
	struct xarray bindings;
	bool exclusive;
};

static int restrictedmem_release(struct inode *inode, struct file *file)
{
	struct restrictedmem *rm = inode->i_mapping->private_data;

	xa_destroy(&rm->bindings);
	kfree(rm);

	WARN_ON_ONCE(rm->backing_f_ops->release);
	return 0;
}

static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
				     loff_t offset, loff_t len)
{
	struct restrictedmem_notifier *notifier;
	unsigned long index;
	pgoff_t start, end;
	int ret;

	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
		return -EINVAL;

	start = offset >> PAGE_SHIFT;
	end = (offset + len) >> PAGE_SHIFT;

	/*
	 * Bindings must be stable across invalidation to ensure the start+end
	 * are balanced.
	 */
	down_read(&rm->lock);

	xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
		notifier->ops->invalidate_start(notifier, start, end);

	ret = rm->backing_f_ops->fallocate(rm->file, mode, offset, len);

	xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
		notifier->ops->invalidate_end(notifier, start, end);

	up_read(&rm->lock);

	return ret;
}

static long restrictedmem_fallocate(struct file *file, int mode,
				    loff_t offset, loff_t len)
{
	struct restrictedmem *rm = file->f_mapping->private_data;

	if (mode & FALLOC_FL_PUNCH_HOLE)
		return restrictedmem_punch_hole(rm, mode, offset, len);

	return rm->backing_f_ops->fallocate(file, mode, offset, len);
}

static int restrictedmem_migrate_folio(struct address_space *mapping,
				       struct folio *dst, struct folio *src,
				       enum migrate_mode)
{
	WARN_ON_ONCE(1);
	return -EINVAL;
}

static int restrictedmem_error_page(struct address_space *mapping,
				    struct page *page)
{
	struct restrictedmem *rm = mapping->private_data;
	struct restrictedmem_notifier *notifier;
	unsigned long index;
	pgoff_t start, end;

	start = page->index;
	end = start + thp_nr_pages(page);

	down_read(&rm->lock);

	xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
		notifier->ops->error(notifier, start, end);

	up_read(&rm->lock);

	return rm->backing_a_ops->error_remove_page(mapping, page);
}

static const struct file_operations restrictedmem_fops = {
	.release = restrictedmem_release,
	.fallocate = restrictedmem_fallocate,
};

static const struct address_space_operations restrictedmem_aops = {
	.dirty_folio = noop_dirty_folio,
#ifdef CONFIG_MIGRATION
	.migrate_folio	= restrictedmem_migrate_folio,
#endif
	.error_remove_page = restrictedmem_error_page,
};

static int restrictedmem_file_create(struct file *file)
{
	struct address_space *mapping = file->f_mapping;
	struct restrictedmem *rm;

	rm = kzalloc(sizeof(*rm), GFP_KERNEL);
	if (!rm)
		return -ENOMEM;

	rm->backing_f_ops = file->f_op;
	rm->backing_a_ops = mapping->a_ops;
	rm->file = file;
	init_rwsem(&rm->lock);
	xa_init(&rm->bindings);

	file->f_flags |= O_LARGEFILE;

	file->f_op = &restrictedmem_fops;
	mapping->a_ops = &restrictedmem_aops;

	mapping_set_unevictable(mapping);
	mapping_set_unmovable(mapping);
	mapping_set_gfp_mask(mapping,
			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
	return 0;
}


static int restrictedmem_create(struct vfsmount *mount)
{
	struct file *file;
	int fd, err;

	fd = get_unused_fd_flags(0);
	if (fd < 0)
		return fd;

	file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0, VM_NORESERVE);
	if (IS_ERR(file)) {
		err = PTR_ERR(file);
		goto err_fd;
	}
	if (WARN_ON_ONCE(file->private_data)) {
		err = -EEXIST;
		goto err_fd;
	}

	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
	file->f_flags |= O_LARGEFILE;

	err = restrictedmem_file_create(file);
	if (err) {
		fput(file);
		goto err_fd;
	}

	fd_install(fd, file);
	return fd;
err_fd:
	put_unused_fd(fd);
	return err;
}

SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
{
	struct vfsmount *mnt;
	struct path *path;
	struct fd f;
	int ret;

	if (flags)
		return -EINVAL;

	f = fdget_raw(mount_fd);
	if (!f.file)
		return -EBADF;

	ret = -EINVAL;

	path = &f.file->f_path;
	if (path->dentry != path->mnt->mnt_root)
		goto out;


	/* Disallow bind-mounts that aren't bind-mounts of the whole filesystem. */
	mnt = path->mnt;
	if (mnt->mnt_root != mnt->mnt_sb->s_root)
		goto out;

	/*
	 * The filesystem must be mounted no-execute, executing from guest
	 * private memory in the host is nonsensical and unsafe.
	 */
	if (!(mnt->mnt_sb->s_iflags & SB_I_NOEXEC))
		goto out;

	/* Currently only TMPFS is supported as underlying storage. */
	if (mnt->mnt_sb->s_magic != TMPFS_MAGIC)
		goto out;

	ret = mnt_want_write(mnt);
	if (ret)
		goto out;

	ret = restrictedmem_create(mnt);

	if (mnt)
		mnt_drop_write(mnt);
out:
	if (f.file)
		fdput(f);

	return ret;
}

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Ackerley Tng]

Christian Brauner <brauner@kernel.org> writes:

> On Wed, Apr 05, 2023 at 09:58:44PM +0000, Ackerley Tng wrote:

>> ...

>> > > Why do you even need this flag? It seems that @mount_fd being < 0 is
>> > > sufficient to indicate that a new restricted memory fd is supposed  
>> to be
>> > > created in the system instance.


>> I'm hoping to have this patch series merged after Chao's patch series
>> introduces the memfd_restricted() syscall [1].

> I'm curious, is there an LSFMM session for this?

As far as I know, there is no LSFMM session for this.

Re: [RFC PATCH v3 1/2] mm: restrictedmem: Allow userspace to specify mount for memfd_restricted

[Sean Christopherson]

On Thu, Apr 13, 2023, Ackerley Tng wrote:
> Christian Brauner <brauner@kernel.org> writes:
> > I'm curious, is there an LSFMM session for this?
> 
> As far as I know, there is no LSFMM session for this.

Correct, no LSFMM session.  In hindsight, that's obviously something we should
have pursued :-(

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Sean Christopherson]

On Tue, Mar 28, 2023, Chao Peng wrote:
> On Fri, Mar 24, 2023 at 10:29:25AM +0800, Xiaoyao Li wrote:
> > On 3/24/2023 10:10 AM, Chao Peng wrote:
> > > On Wed, Mar 22, 2023 at 05:41:31PM -0700, Isaku Yamahata wrote:
> > > > On Wed, Mar 08, 2023 at 03:40:26PM +0800,
> > > > Chao Peng <chao.p.peng@linux.intel.com> wrote:
> > > > 
> > > > > On Wed, Mar 08, 2023 at 12:13:24AM +0000, Ackerley Tng wrote:
> > > > > > Chao Peng <chao.p.peng@linux.intel.com> writes:
> > > > > > 
> > > > > > > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> > > > > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > > > +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
> > > > > > > +{
> > > > > > > +	if (!offset)
> > > > > > > +		return true;
> > > > > > > +	if (!gpa)
> > > > > > > +		return false;
> > > > > > > +
> > > > > > > +	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
> > > > 
> > > > This check doesn't work expected. For example, offset = 2GB, gpa=4GB
> > > > this check fails.
> > > 
> > > This case is expected to fail as Sean initially suggested[*]:
> > >    I would rather reject memslot if the gfn has lesser alignment than
> > >    the offset. I'm totally ok with this approach _if_ there's a use case.
> > >    Until such a use case presents itself, I would rather be conservative
> > >    from a uAPI perspective.
> > > 
> > > I understand that we put tighter restriction on this but if you see such
> > > restriction is really a big issue for real usage, instead of a
> > > theoretical problem, then we can loosen the check here. But at that time
> > > below code is kind of x86 specific and may need improve.
> > > 
> > > BTW, in latest code, I replaced count_trailing_zeros() with fls64():
> > >    return !!(fls64(offset) >= fls64(gpa));
> > 
> > wouldn't it be !!(ffs64(offset) <= ffs64(gpa)) ?
> 
> As the function document explains, here we want to return true when
> ALIGNMENT(offset) >= ALIGNMENT(gpa), so '>=' is what we need.
> 
> It's worthy clarifying that in Sean's original suggestion he actually
> mentioned the opposite. He said 'reject memslot if the gfn has lesser
> alignment than the offset', but I wonder this is his purpose, since
> if ALIGNMENT(offset) < ALIGNMENT(gpa), we wouldn't be possible to map
> the page as largepage. Consider we have below config:
> 
>   gpa=2M, offset=1M
> 
> In this case KVM tries to map gpa at 2M as 2M hugepage but the physical
> page at the offset(1M) in private_fd cannot provide the 2M page due to
> misalignment.
> 
> But as we discussed in the off-list thread, here we do find a real use
> case indicating this check is too strict. i.e. QEMU immediately fails
> when launch a guest > 2G memory. For this case QEMU splits guest memory
> space into two slots:
> 
>   Slot#1(ram_below_4G): gpa=0x0, offset=0x0, size=2G
>   Slot#2(ram_above_4G): gpa=4G,  offset=2G,  size=totalsize-2G
> 
> This strict alignment check fails for slot#2 because offset(2G) has less
> alignment than gpa(4G). To allow this, one solution can revert to my
> previous change in kvm_alloc_memslot_metadata() to disallow hugepage
> only when the offset/gpa are not aligned to related page size.
> 
> Sean, How do you think?

I agree, a pure alignment check is too restrictive, and not really what I intended
despite past me literally saying that's what I wanted :-)  I think I may have also
inverted the "less alignment" statement, but luckily I believe that ends up being
a moot point.

The goal is to avoid having to juggle scenarios where KVM wants to create a hugepage,
but restrictedmem can't provide one because of a misaligned file offset.  I think
the rule we want is that the offset must be aligned to the largest page size allowed
by the memslot _size_.  E.g. on x86, if the memslot size is >=1GiB then the offset
must be 1GiB or beter, ditto for >=2MiB and >=4KiB (ignoring that 4KiB is already a
requirement).

We could loosen that to say the largest size allowed by the memslot, but I don't
think that's worth the effort unless it's trivially easy to implement in code,
e.g. KVM could technically allow a 4KiB aligned offset if the memslot is 2MiB
sized but only 4KiB aligned on the GPA.  I doubt there's a real use case for such
a memslot, so I want to disallow that unless it's super easy to implement.

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Ackerley Tng]

Sean Christopherson <seanjc@google.com> writes:

> On Thu, Apr 13, 2023, Christian Brauner wrote:
>> On Thu, Aug 18, 2022 at 04:24:21PM +0300, Kirill A . Shutemov wrote:
>> > On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote:
>> > > Here's what I would prefer, and imagine much easier for you to  
>> maintain;
>> > > but I'm no system designer, and may be misunderstanding throughout.
>> > >
>> > > QEMU gets fd from opening /dev/kvm_something, uses ioctls (or perhaps
>> > > the fallocate syscall interface itself) to allocate and free the  
>> memory,
>> > > ioctl for initializing some of it too.  KVM in control of whether  
>> that
>> > > fd can be read or written or mmap'ed or whatever, no need to prevent  
>> it
>> > > in shmem.c, no need for flags, seals, notifications to and fro  
>> because
>> > > KVM is already in control and knows the history.  If shmem actually  
>> has
>> > > value, call into it underneath - somewhat like SysV SHM, and  
>> /dev/zero
>> > > mmap, and i915/gem make use of it underneath.  If shmem has nothing  
>> to
>> > > add, just allocate and free kernel memory directly, recorded in your
>> > > own xarray.
>> >
>> > I guess shim layer on top of shmem *can* work. I don't see immediately  
>> why
>> > it would not. But I'm not sure it is right direction. We risk creating  
>> yet
>> > another parallel VM with own rules/locking/accounting that opaque to
>> > core-mm.

>> Sorry for necrobumping this thread but I've been reviewing the

> No worries, I'm just stoked someone who actually knows what they're doing  
> is
> chiming in :-)


+1, thanks Christian!

>> memfd_restricted() extension that Ackerley is currently working on. I
>> was pointed to this thread as this is what the extension is building
>> on but I'll reply to both threads here.

>>  From a glance at v10, memfd_restricted() is currently implemented as an
>> in-kernel stacking filesystem. A call to memfd_restricted() creates a
>> new restricted memfd file and a new unlinked tmpfs file and stashes the
>> tmpfs file into the memfd file's private data member. It then uses the
>> tmpfs file's f_ops and i_ops to perform the relevant file and inode
>> operations. So it has the same callstack as a general stacking
>> filesystem like overlayfs in some cases:

>>          memfd_restricted->getattr()
>>          -> tmpfs->getattr()

> ...

>> Since you're effectively acting like a stacking filesystem you should
>> really use the device number of your memfd restricted filesystem. IOW,
>> sm like:

>>          stat->dev = memfd_restricted_dentry->d_sb->s_dev;

>> But then you run into trouble if you want to go forward with Ackerley's
>> extension that allows to explicitly pass in tmpfs fds to
>> memfd_restricted(). Afaict, two tmpfs instances might allocate the same
>> inode number. So now the inode and device number pair isn't unique
>> anymore.

>> So you might best be served by allocating and reporting your own inode
>> numbers as well.

>> But if you want to preserve the inode number and device number of the
>> relevant tmpfs instance but still report memfd restricted as your
>> filesystem type

> Unless I missed something along the way, reporting memfd_restricted as a  
> distinct
> filesystem is very much a non-goal.  AFAIK it's purely a side effect of  
> the
> proposed implementation.

>> then I think it's reasonable to ask whether a stacking implementation  
>> really
>> makes sense here.

>> If you extend memfd_restricted() or even consider extending it in the
>> future to take tmpfs file descriptors as arguments to identify the tmpfs
>> instance in which to allocate the underlying tmpfs file for the new
>> restricted memfd file you should really consider a tmpfs based
>> implementation.

>> Because at that point it just feels like a pointless wrapper to get
>> custom f_ops and i_ops. Plus it's wasteful because you allocate dentries
>> and inodes that you don't really care about at all.

>> Just off the top of my hat you might be better served:
>> * by a new ioctl() on tmpfs instances that
>>    yield regular tmpfs file descriptors with restricted f_ops and i_ops.
>>    That's not that different from btrfs subvolumes which effectively are
>>    directories but are created through an ioctl().

> I think this is more or less what we want to do, except via a dedicated  
> syscall
> instead of an ioctl() so that the primary interface isn't strictly tied  
> to tmpfs,
> e.g. so that it can be extended to other backing types in the future.

>> * by a mount option to tmpfs that makes it act
>>    in this restricted manner then you don't need an ioctl() and can get
>>    away with regular open calls. Such a tmpfs instance would only create
>>    regular, restricted memfds.

> I'd prefer to not go this route, becuase IIUC, it would require  
> relatively invasive
> changes to shmem code, and IIUC would require similar changes to other  
> support
> backings in the future, e.g. hugetlbfs?  And as above, I don't think any  
> of the
> potential use cases need restrictedmem to be a uniquely identifiable
> mount.

FWIW, I'm starting to look at extending restrictedmem to hugetlbfs and
the separation that the current implementation has is very helpful. Also
helps that hugetlbfs and tmpfs are structured similarly, I guess.


> One of the goals (hopefully not a pipe dream) is to design restrictmem in  
> such a
> way that extending it to support other backing types isn't terribly  
> difficult.
> In case it's not obvious, most of us working on this stuff aren't  
> filesystems
> experts, and many of us aren't mm experts either.  The more we (KVM folks  
> for the
> most part) can leverage existing code to do the heavy lifting, the better.

> After giving myself a bit of a crash course in file systems, would  
> something like
> the below have any chance of (a) working, (b) getting merged, and (c)  
> being
> maintainable?

> The idea is similar to a stacking filesystem, but instead of stacking,  
> restrictedmem
> hijacks a f_ops and a_ops to create a lightweight shim around tmpfs.   
> There are
> undoubtedly issues and edge cases, I'm just looking for a quick "yes,  
> this might
> be doable" or a "no, that's absolutely bonkers, don't try it".

Not an FS expert by any means, but I did think of approaching it this
way as well!

"Hijacking" perhaps gives this approach a bit of a negative
connotation. I thought this is pretty close to subclassing (as in Object
Oriented Programming). When some methods (e.g. fallocate) are called,
restrictedmem does some work, and calls the same method in the
superclass.

The existing restrictedmem code is a more like instantiating an shmem
object and keeping that object as a field within the restrictedmem
object.

Some (maybe small) issues I can think of now:

(1)

One difficulty with this approach is that other functions may make
assumptions about private_data being of a certain type, or functions may
use private_data.

I checked and IIUC neither shmem nor hugetlbfs use the private_data
field in the inode's i_mapping (also file's f_mapping).

But there's fs/buffer.c which uses private_data, although those
functions seem to be used by FSes like ext4 and fat, not memory-backed
FSes.

We can probably fix this if any backing filesystems of restrictedmem,
like tmpfs and future ones use private_data.

Could the solution here be to store private_data of the superclass
instance in restrictedmem, and then override every method in the
superclass that uses private_data to first restore private_data before
making the superclass call? Perhaps we can take private_lock to change
private_data.

(2)

Perhaps there are other slightly hidden cases that might need cleaning up.

For example, one of the patches in this series amends the
shmem_mapping() function from

return mapping->a_ops == &shmem_aops;

to

return mapping->host->i_sb->s_magic == TMPFS_MAGIC;

The former/original is more accurate since it checks a property of the
mapping itself instead of checking a property of the mapping's host's
superblock.

The impact of changing this guard is more obvious if we now override
a_ops but keep the mapping's host's superblock's s_magic.

Specifically for this example, maybe we should handle restrictedmem in
the caller (me_pagecache_clean()) specially, in addition to shmem.


> Thanks!


> struct restrictedmem {
> 	struct rw_semaphore lock;
> 	struct file *file;
> 	const struct file_operations *backing_f_ops;
> 	const struct address_space_operations *backing_a_ops;
> 	struct xarray bindings;
> 	bool exclusive;
> };

> static int restrictedmem_release(struct inode *inode, struct file *file)
> {
> 	struct restrictedmem *rm = inode->i_mapping->private_data;

> 	xa_destroy(&rm->bindings);
> 	kfree(rm);

> 	WARN_ON_ONCE(rm->backing_f_ops->release);
> 	return 0;
> }

> static long restrictedmem_punch_hole(struct restrictedmem *rm, int mode,
> 				     loff_t offset, loff_t len)
> {
> 	struct restrictedmem_notifier *notifier;
> 	unsigned long index;
> 	pgoff_t start, end;
> 	int ret;

> 	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> 		return -EINVAL;

> 	start = offset >> PAGE_SHIFT;
> 	end = (offset + len) >> PAGE_SHIFT;

> 	/*
> 	 * Bindings must be stable across invalidation to ensure the start+end
> 	 * are balanced.
> 	 */
> 	down_read(&rm->lock);

> 	xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
> 		notifier->ops->invalidate_start(notifier, start, end);

> 	ret = rm->backing_f_ops->fallocate(rm->file, mode, offset, len);

> 	xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
> 		notifier->ops->invalidate_end(notifier, start, end);

> 	up_read(&rm->lock);

> 	return ret;
> }

> static long restrictedmem_fallocate(struct file *file, int mode,
> 				    loff_t offset, loff_t len)
> {
> 	struct restrictedmem *rm = file->f_mapping->private_data;

> 	if (mode & FALLOC_FL_PUNCH_HOLE)
> 		return restrictedmem_punch_hole(rm, mode, offset, len);

> 	return rm->backing_f_ops->fallocate(file, mode, offset, len);
> }

> static int restrictedmem_migrate_folio(struct address_space *mapping,
> 				       struct folio *dst, struct folio *src,
> 				       enum migrate_mode)
> {
> 	WARN_ON_ONCE(1);
> 	return -EINVAL;
> }

> static int restrictedmem_error_page(struct address_space *mapping,
> 				    struct page *page)
> {
> 	struct restrictedmem *rm = mapping->private_data;
> 	struct restrictedmem_notifier *notifier;
> 	unsigned long index;
> 	pgoff_t start, end;

> 	start = page->index;
> 	end = start + thp_nr_pages(page);

> 	down_read(&rm->lock);

> 	xa_for_each_range(&rm->bindings, index, notifier, start, end - 1)
> 		notifier->ops->error(notifier, start, end);

> 	up_read(&rm->lock);

> 	return rm->backing_a_ops->error_remove_page(mapping, page);
> }

When I was thinking of this I was stuck on handling error_remove_page,
because it was looking up the superblock to iterate over the inodes to
find the right mapping. Glad to see that the solution is simply to use
the given mapping from the arguments!


> static const struct file_operations restrictedmem_fops = {
> 	.release = restrictedmem_release,
> 	.fallocate = restrictedmem_fallocate,
> };

> static const struct address_space_operations restrictedmem_aops = {
> 	.dirty_folio = noop_dirty_folio,
> #ifdef CONFIG_MIGRATION
> 	.migrate_folio	= restrictedmem_migrate_folio,
> #endif
> 	.error_remove_page = restrictedmem_error_page,
> };

> static int restrictedmem_file_create(struct file *file)
> {
> 	struct address_space *mapping = file->f_mapping;
> 	struct restrictedmem *rm;

> 	rm = kzalloc(sizeof(*rm), GFP_KERNEL);
> 	if (!rm)
> 		return -ENOMEM;

> 	rm->backing_f_ops = file->f_op;
> 	rm->backing_a_ops = mapping->a_ops;
> 	rm->file = file;

We don't really need to do this, since rm->file is already the same as
file, we could just pass the file itself when it's needed

> 	init_rwsem(&rm->lock);
> 	xa_init(&rm->bindings);

> 	file->f_flags |= O_LARGEFILE;

> 	file->f_op = &restrictedmem_fops;
> 	mapping->a_ops = &restrictedmem_aops;

I think we probably have to override inode_operations as well, because
otherwise other methods would become available to a restrictedmem file
(like link, unlink, mkdir, tmpfile). Or maybe that's a feature instead
of a bug.


> 	mapping_set_unevictable(mapping);
> 	mapping_set_unmovable(mapping);
> 	mapping_set_gfp_mask(mapping,
> 			     mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> 	return 0;
> }


> static int restrictedmem_create(struct vfsmount *mount)
> {
> 	struct file *file;
> 	int fd, err;

> 	fd = get_unused_fd_flags(0);
> 	if (fd < 0)
> 		return fd;

> 	file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0,  
> VM_NORESERVE);
> 	if (IS_ERR(file)) {
> 		err = PTR_ERR(file);
> 		goto err_fd;
> 	}
> 	if (WARN_ON_ONCE(file->private_data)) {
> 		err = -EEXIST;
> 		goto err_fd;
> 	}

Did you intend this as a check that the backing filesystem isn't using
the private_data field in the mapping?

I think you meant file->f_mapping->private_data.

On this note, we will probably have to fix things whenever any backing
filesystems need the private_data field.


> 	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
> 	file->f_flags |= O_LARGEFILE;

> 	err = restrictedmem_file_create(file);
> 	if (err) {
> 		fput(file);
> 		goto err_fd;
> 	}

> 	fd_install(fd, file);
> 	return fd;
> err_fd:
> 	put_unused_fd(fd);
> 	return err;
> }

> SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, int, mount_fd)
> {
> 	struct vfsmount *mnt;
> 	struct path *path;
> 	struct fd f;
> 	int ret;

> 	if (flags)
> 		return -EINVAL;

> 	f = fdget_raw(mount_fd);
> 	if (!f.file)
> 		return -EBADF;

> 	ret = -EINVAL;

> 	path = &f.file->f_path;
> 	if (path->dentry != path->mnt->mnt_root)
> 		goto out;


> 	/* Disallow bind-mounts that aren't bind-mounts of the whole filesystem.  
> */
> 	mnt = path->mnt;
> 	if (mnt->mnt_root != mnt->mnt_sb->s_root)
> 		goto out;

> 	/*
> 	 * The filesystem must be mounted no-execute, executing from guest
> 	 * private memory in the host is nonsensical and unsafe.
> 	 */
> 	if (!(mnt->mnt_sb->s_iflags & SB_I_NOEXEC))
> 		goto out;

> 	/* Currently only TMPFS is supported as underlying storage. */
> 	if (mnt->mnt_sb->s_magic != TMPFS_MAGIC)
> 		goto out;

> 	ret = mnt_want_write(mnt);
> 	if (ret)
> 		goto out;

> 	ret = restrictedmem_create(mnt);

> 	if (mnt)
> 		mnt_drop_write(mnt);
> out:
> 	if (f.file)
> 		fdput(f);

> 	return ret;
> }

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Sean Christopherson]

On Fri, Apr 14, 2023, Ackerley Tng wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > On Thu, Apr 13, 2023, Christian Brauner wrote:
> > > * by a mount option to tmpfs that makes it act
> > >    in this restricted manner then you don't need an ioctl() and can get
> > >    away with regular open calls. Such a tmpfs instance would only create
> > >    regular, restricted memfds.
> 
> > I'd prefer to not go this route, becuase IIUC, it would require relatively
> > invasive changes to shmem code, and IIUC would require similar changes to
> > other support backings in the future, e.g. hugetlbfs?  And as above, I
> > don't think any of the potential use cases need restrictedmem to be a
> > uniquely identifiable mount.
> 
> FWIW, I'm starting to look at extending restrictedmem to hugetlbfs and
> the separation that the current implementation has is very helpful. Also
> helps that hugetlbfs and tmpfs are structured similarly, I guess.
> 
> > One of the goals (hopefully not a pipe dream) is to design restrictmem in
> > such a way that extending it to support other backing types isn't terribly
> > difficult.  In case it's not obvious, most of us working on this stuff
> > aren't filesystems experts, and many of us aren't mm experts either.  The
> > more we (KVM folks for the most part) can leverage existing code to do the
> > heavy lifting, the better.
> 
> > After giving myself a bit of a crash course in file systems, would
> > something like the below have any chance of (a) working, (b) getting
> > merged, and (c) being maintainable?
> 
> > The idea is similar to a stacking filesystem, but instead of stacking,
> > restrictedmem hijacks a f_ops and a_ops to create a lightweight shim around
> > tmpfs.  There are undoubtedly issues and edge cases, I'm just looking for a
> > quick "yes, this might be doable" or a "no, that's absolutely bonkers,
> > don't try it".
> 
> Not an FS expert by any means, but I did think of approaching it this
> way as well!
> 
> "Hijacking" perhaps gives this approach a bit of a negative connotation.

Heh, commandeer then.

> I thought this is pretty close to subclassing (as in Object
> Oriented Programming). When some methods (e.g. fallocate) are called,
> restrictedmem does some work, and calls the same method in the
> superclass.
> 
> The existing restrictedmem code is a more like instantiating an shmem
> object and keeping that object as a field within the restrictedmem
> object.
> 
> Some (maybe small) issues I can think of now:
> 
> (1)
> 
> One difficulty with this approach is that other functions may make
> assumptions about private_data being of a certain type, or functions may
> use private_data.
> 
> I checked and IIUC neither shmem nor hugetlbfs use the private_data
> field in the inode's i_mapping (also file's f_mapping).
> 
> But there's fs/buffer.c which uses private_data, although those
> functions seem to be used by FSes like ext4 and fat, not memory-backed
> FSes.
> 
> We can probably fix this if any backing filesystems of restrictedmem,
> like tmpfs and future ones use private_data.

Ya, if we go the route of poking into f_ops and stuff, I would want to add
WARN_ON_ONCE() hardening of everything that restrictemem wants to "commandeer" ;-)

> > static int restrictedmem_file_create(struct file *file)
> > {
> > 	struct address_space *mapping = file->f_mapping;
> > 	struct restrictedmem *rm;
> 
> > 	rm = kzalloc(sizeof(*rm), GFP_KERNEL);
> > 	if (!rm)
> > 		return -ENOMEM;
> 
> > 	rm->backing_f_ops = file->f_op;
> > 	rm->backing_a_ops = mapping->a_ops;
> > 	rm->file = file;
> 
> We don't really need to do this, since rm->file is already the same as
> file, we could just pass the file itself when it's needed

Aha!  I was working on getting rid of it, but forgot to go back and do another
pass.

> > 	init_rwsem(&rm->lock);
> > 	xa_init(&rm->bindings);
> 
> > 	file->f_flags |= O_LARGEFILE;
> 
> > 	file->f_op = &restrictedmem_fops;
> > 	mapping->a_ops = &restrictedmem_aops;
> 
> I think we probably have to override inode_operations as well, because
> otherwise other methods would become available to a restrictedmem file
> (like link, unlink, mkdir, tmpfile). Or maybe that's a feature instead
> of a bug.

I think we want those?  What we want to restrict are operations that require
read/write/execute access to the file, everything else should be ok. fallocate()
is a special case because restrictmem needs to tell KVM to unmap the memory when
a hole is punched.  I assume ->setattr() needs similar treatment to handle
ftruncate()?

I'd love to hear Christian's input on this aspect of things.

> > 	if (WARN_ON_ONCE(file->private_data)) {
> > 		err = -EEXIST;
> > 		goto err_fd;
> > 	}
> 
> Did you intend this as a check that the backing filesystem isn't using
> the private_data field in the mapping?
>
> I think you meant file->f_mapping->private_data.

Ya, sounds right.  I should have added disclaimers that (a) I wrote this quite
quickly and (b) it's compile tested only at this point.

> On this note, we will probably have to fix things whenever any backing
> filesystems need the private_data field.

Yep.

> > 	f = fdget_raw(mount_fd);
> > 	if (!f.file)
> > 		return -EBADF;

...

> > 	/*
> > 	 * The filesystem must be mounted no-execute, executing from guest
> > 	 * private memory in the host is nonsensical and unsafe.
> > 	 */
> > 	if (!(mnt->mnt_sb->s_iflags & SB_I_NOEXEC))
> > 		goto out;

Looking at this more closely, I don't think we need to require NOEXEC, things like
like execve() should get squashed by virtue of not providing any read/write
implementations.  And dropping my misguided NOEXEC requirement means there's no
reason to disallow using the kernel internal mount.

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Sean Christopherson]

On Fri, Apr 14, 2023, Sean Christopherson wrote:
> On Fri, Apr 14, 2023, Ackerley Tng wrote:
> > Sean Christopherson <seanjc@google.com> writes:
> > > 	if (WARN_ON_ONCE(file->private_data)) {
> > > 		err = -EEXIST;
> > > 		goto err_fd;
> > > 	}
> > 
> > Did you intend this as a check that the backing filesystem isn't using
> > the private_data field in the mapping?
> >
> > I think you meant file->f_mapping->private_data.
> 
> Ya, sounds right.  I should have added disclaimers that (a) I wrote this quite
> quickly and (b) it's compile tested only at this point.

FWIW, here's a very lightly tested version that doesn't explode on a basic selftest.

https://github.com/sean-jc/linux/tree/x86/upm_base_support

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Chao Peng]

On Tue, Jan 24, 2023 at 01:27:50AM +0000, Sean Christopherson wrote:
> On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > On Thu, Jan 19, 2023 at 03:25:08PM +0000,
> > Sean Christopherson <seanjc@google.com> wrote:
> > 
> > > On Thu, Jan 19, 2023, Isaku Yamahata wrote:
> > > > On Sat, Jan 14, 2023 at 12:37:59AM +0000,
> > > > Sean Christopherson <seanjc@google.com> wrote:
> > > > 
> > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
> > > > > > This patch series implements KVM guest private memory for confidential
> > > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
> > > > > > TDX-protected guest memory, machine check can happen which can further
> > > > > > crash the running host system, this is terrible for multi-tenant
> > > > > > configurations. The host accesses include those from KVM userspace like
> > > > > > QEMU. This series addresses KVM userspace induced crash by introducing
> > > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
> > > > > > via a fd-based approach, but it can never access the guest memory
> > > > > > content.
> > > > > > 
> > > > > > The patch series touches both core mm and KVM code. I appreciate
> > > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
> > > > > > reviews are always welcome.
> > > > > >   - 01: mm change, target for mm tree
> > > > > >   - 02-09: KVM change, target for KVM tree
> > > > > 
> > > > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
> > > > > is available here:
> > > > > 
> > > > >   git@github.com:sean-jc/linux.git x86/upm_base_support
> > > > > 
> > > > > It compiles and passes the selftest, but it's otherwise barely tested.  There are
> > > > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
> > > > > a WIP.
> > > > > 
> > > > > As for next steps, can you (handwaving all of the TDX folks) take a look at what
> > > > > I pushed and see if there's anything horrifically broken, and that it still works
> > > > > for TDX?
> > > > > 
> > > > > Fuad (and pKVM folks) same ask for you with respect to pKVM.  Absolutely no rush
> > > > > (and I mean that).
> > > > > 
> > > > > On my side, the two things on my mind are (a) tests and (b) downstream dependencies
> > > > > (SEV and TDX).  For tests, I want to build a lists of tests that are required for
> > > > > merging so that the criteria for merging are clear, and so that if the list is large
> > > > > (haven't thought much yet), the work of writing and running tests can be distributed.
> > > > > 
> > > > > Regarding downstream dependencies, before this lands, I want to pull in all the
> > > > > TDX and SNP series and see how everything fits together.  Specifically, I want to
> > > > > make sure that we don't end up with a uAPI that necessitates ugly code, and that we
> > > > > don't miss an opportunity to make things simpler.  The patches in the SNP series to
> > > > > add "legacy" SEV support for UPM in particular made me slightly rethink some minor
> > > > > details.  Nothing remotely major, but something that needs attention since it'll
> > > > > be uAPI.
> > > > 
> > > > Although I'm still debuging with TDX KVM, I needed the following.
> > > > kvm_faultin_pfn() is called without mmu_lock held.  the race to change
> > > > private/shared is handled by mmu_seq.  Maybe dedicated function only for
> > > > kvm_faultin_pfn().
> > > 
> > > Gah, you're not on the other thread where this was discussed[*].  Simply deleting
> > > the lockdep assertion is safe, for guest types that rely on the attributes to
> > > define shared vs. private, KVM rechecks the attributes under the protection of
> > > mmu_seq.
> > > 
> > > I'll get a fixed version pushed out today.
> > > 
> > > [*] https://lore.kernel.org/all/Y8gpl+LwSuSgBFks@google.com
> > 
> > Now I have tdx kvm working. I've uploaded at the followings.
> > It's rebased to v6.2-rc3.
> >         git@github.com:yamahata/linux.git tdx/upm
> >         git@github.com:yamahata/qemu.git tdx/upm
> 
> And I finally got a working, building version updated and pushed out (again to):
> 
>   git@github.com:sean-jc/linux.git x86/upm_base_support
> 
> Took longer than expected to get the memslot restrictions sussed out.  I'm done
> working on the code for now, my plan is to come back to it+TDX+SNP in 2-3 weeks
> to resolves any remaining todos (that no one else tackles) and to do the whole
> "merge the world" excersise.

Hi Sean,

In case you started working on the code again, I have a branch [1]
originally planned as v11 candidate which I believe I addressed all the
discussions we had for v10 except the very latest one [2] and integrated
all the newly added selftests from Ackerley and myself. The branch was
based on your original upm_base_support and then rebased to your
kvm-x86/mmu head. Feel free to take anything you think useful( most of
them are trivial things but also some fixes for bugs).

[1] https://github.com/chao-p/linux/commits/privmem-v11.6
[2] https://lore.kernel.org/all/20230413160405.h6ov2yl6l3i7mvsj@box.shutemov.name/

Chao
> 
> > kvm_mmu_do_page_fault() needs the following change.
> > kvm_mem_is_private() queries mem_attr_array.  kvm_faultin_pfn() also uses
> > kvm_mem_is_private(). So the shared-private check in kvm_faultin_pfn() doesn't
> > make sense. This change would belong to TDX KVM patches, though.
> 
> Yeah, SNP needs similar treatment.  Sorting that out is high up on the todo list.

Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

[Sean Christopherson]

On Mon, Apr 17, 2023, Chao Peng wrote:
> In case you started working on the code again, I have a branch [1]
> originally planned as v11 candidate which I believe I addressed all the
> discussions we had for v10 except the very latest one [2] and integrated
> all the newly added selftests from Ackerley and myself. The branch was
> based on your original upm_base_support and then rebased to your
> kvm-x86/mmu head. Feel free to take anything you think useful( most of
> them are trivial things but also some fixes for bugs).

Nice!  I am going to work on splicing together the various series this week, I'll
make sure to grab your work.

Thanks much! 

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Ackerley Tng]

Sean Christopherson <seanjc@google.com> writes:

> On Tue, Mar 28, 2023, Chao Peng wrote:
>> On Fri, Mar 24, 2023 at 10:29:25AM +0800, Xiaoyao Li wrote:
>> > On 3/24/2023 10:10 AM, Chao Peng wrote:
>> > > On Wed, Mar 22, 2023 at 05:41:31PM -0700, Isaku Yamahata wrote:
>> > > > On Wed, Mar 08, 2023 at 03:40:26PM +0800,
>> > > > Chao Peng <chao.p.peng@linux.intel.com> wrote:
>> > > >
>> > > > > On Wed, Mar 08, 2023 at 12:13:24AM +0000, Ackerley Tng wrote:
>> > > > > > Chao Peng <chao.p.peng@linux.intel.com> writes:
>> > > > > >
>> > > > > > > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean  
>> Christopherson wrote:
>> > > > > > > > On Fri, Dec 02, 2022, Chao Peng wrote:
>> > > > > > > +static bool kvm_check_rmem_offset_alignment(u64 offset, u64  
>> gpa)
>> > > > > > > +{
>> > > > > > > +	if (!offset)
>> > > > > > > +		return true;
>> > > > > > > +	if (!gpa)
>> > > > > > > +		return false;
>> > > > > > > +
>> > > > > > > +	return !!(count_trailing_zeros(offset) >=  
>> count_trailing_zeros(gpa));
>> > > >
>> > > > This check doesn't work expected. For example, offset = 2GB,  
>> gpa=4GB
>> > > > this check fails.
>> > >
>> > > This case is expected to fail as Sean initially suggested[*]:
>> > >    I would rather reject memslot if the gfn has lesser alignment than
>> > >    the offset. I'm totally ok with this approach _if_ there's a use  
>> case.
>> > >    Until such a use case presents itself, I would rather be  
>> conservative
>> > >    from a uAPI perspective.
>> > >
>> > > I understand that we put tighter restriction on this but if you see  
>> such
>> > > restriction is really a big issue for real usage, instead of a
>> > > theoretical problem, then we can loosen the check here. But at that  
>> time
>> > > below code is kind of x86 specific and may need improve.
>> > >
>> > > BTW, in latest code, I replaced count_trailing_zeros() with fls64():
>> > >    return !!(fls64(offset) >= fls64(gpa));
>> >
>> > wouldn't it be !!(ffs64(offset) <= ffs64(gpa)) ?

>> As the function document explains, here we want to return true when
>> ALIGNMENT(offset) >= ALIGNMENT(gpa), so '>=' is what we need.

>> It's worthy clarifying that in Sean's original suggestion he actually
>> mentioned the opposite. He said 'reject memslot if the gfn has lesser
>> alignment than the offset', but I wonder this is his purpose, since
>> if ALIGNMENT(offset) < ALIGNMENT(gpa), we wouldn't be possible to map
>> the page as largepage. Consider we have below config:

>>    gpa=2M, offset=1M

>> In this case KVM tries to map gpa at 2M as 2M hugepage but the physical
>> page at the offset(1M) in private_fd cannot provide the 2M page due to
>> misalignment.

>> But as we discussed in the off-list thread, here we do find a real use
>> case indicating this check is too strict. i.e. QEMU immediately fails
>> when launch a guest > 2G memory. For this case QEMU splits guest memory
>> space into two slots:

>>    Slot#1(ram_below_4G): gpa=0x0, offset=0x0, size=2G
>>    Slot#2(ram_above_4G): gpa=4G,  offset=2G,  size=totalsize-2G

>> This strict alignment check fails for slot#2 because offset(2G) has less
>> alignment than gpa(4G). To allow this, one solution can revert to my
>> previous change in kvm_alloc_memslot_metadata() to disallow hugepage
>> only when the offset/gpa are not aligned to related page size.

>> Sean, How do you think?

> I agree, a pure alignment check is too restrictive, and not really what I  
> intended
> despite past me literally saying that's what I wanted :-)  I think I may  
> have also
> inverted the "less alignment" statement, but luckily I believe that ends  
> up being
> a moot point.

> The goal is to avoid having to juggle scenarios where KVM wants to create  
> a hugepage,
> but restrictedmem can't provide one because of a misaligned file offset.   
> I think
> the rule we want is that the offset must be aligned to the largest page  
> size allowed
> by the memslot _size_.  E.g. on x86, if the memslot size is >=1GiB then  
> the offset
> must be 1GiB or beter, ditto for >=2MiB and >=4KiB (ignoring that 4KiB is  
> already a
> requirement).

> We could loosen that to say the largest size allowed by the memslot, but  
> I don't
> think that's worth the effort unless it's trivially easy to implement in  
> code,
> e.g. KVM could technically allow a 4KiB aligned offset if the memslot is  
> 2MiB
> sized but only 4KiB aligned on the GPA.  I doubt there's a real use case  
> for such
> a memslot, so I want to disallow that unless it's super easy to implement.

Checking my understanding here about why we need this alignment check:

When KVM requests a page from restrictedmem, KVM will provide an offset
into the file in terms of 4K pages.

When shmem is configured to use hugepages, shmem_get_folio() will round
the requested offset down to the nearest hugepage-aligned boundary in
shmem_alloc_hugefolio().

Example of problematic configuration provided to
KVM_SET_USER_MEMORY_REGION2:

+ shmem configured to use 1GB pages
+ restrictedmem_offset provided to KVM_SET_USER_MEMORY_REGION2: 0x4000
+ memory_size provided in KVM_SET_USER_MEMORY_REGION2: 1GB
+ KVM requests offset (pgoff_t) 0x8, which translates to offset 0x8000

restrictedmem_get_page() and shmem_get_folio() returns the page for
offset 0x0 in the file, since rounding down 0x8000 to the nearest 1GB is
0x0. This is allocating outside the range that KVM is supposed to use,
since the parameters provided in KVM_SET_USER_MEMORY_REGION2 is only
supposed to be offset 0x4000 to (0x4000 + 1GB = 0x40004000) in the file.

IIUC shmem will actually just round down (0x4000 rounded down to nearest
1GB will be 0x0) and allocate without checking bounds, so if offset 0x0
to 0x4000 in the file were supposed to be used by something else, there
might be issues.

Hence, this alignment check ensures that rounding down of any offsets
provided by KVM (based on page size configured in the backing file
provided) to restrictedmem_get_page() must not go below the offset
provided to KVM_SET_USER_MEMORY_REGION2.

Enforcing alignment of restrictedmem_offset based on the currently-set
page size in the backing file (i.e. shmem) may not be effective, since
the size of the pages in the backing file can be adjusted to a larger
size after KVM_SET_USER_MEMORY_REGION2 succeeds. With that, we may still
end up allocating outside the range that KVM was provided with.

Hence, to be safe, we should check alignment to the max page size across
all backing filesystems, so the constraint is

     rounding down restrictedmem_offset to
     min(max page size across all backing filesystems,
         max page size that fits in memory_size) == restrictedmem_offset

which is the same check as

     restrictedmem_offset must be aligned to min(max page size across all
     backing filesystems, max page size that fits in memory_size)

which can safely reduce to

     restrictedmem_offset must be aligned to max page size that fits in
     memory_size

since "max page size that fits in memory_size" is probably <= to "max
page size across all backing filesystems", and if it's larger, it'll
just be a tighter constraint.

If the above understanding is correct:

+ We must enforce this in the KVM_SET_USER_MEMORY_REGION2 handler, since
   IIUC shmem will just round down and allocate without checking bounds.

     + I think this is okay because holes in the restrictedmem file (in
       terms of offset) made to accommodate this constraint don't cost us
       anything anyway(?) Are they just arbitrary offsets in a file? In
       our case, this file is usually a new and empty file.

     + In the case of migration of a restrictedmem file between two KVM
       VMs, this constraint would cause a problem is if the largest
       possible page size on the destination machine is larger than that
       of the source machine. In that case, we might have to move the
       data in the file to a different offset (a separate problem).

+ On this note, it seems like there is no check for when the range is
   smaller than the allocated page? Like if the range provided is 4KB in
   size, but shmem is then configured to use a 1GB page, will we end up
   allocating past the end of the range?

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Christian Brauner]

On Thu, Apr 13, 2023 at 03:28:43PM -0700, Sean Christopherson wrote:
> On Thu, Apr 13, 2023, Christian Brauner wrote:
> > On Thu, Aug 18, 2022 at 04:24:21PM +0300, Kirill A . Shutemov wrote:
> > > On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote:
> > > > Here's what I would prefer, and imagine much easier for you to maintain;
> > > > but I'm no system designer, and may be misunderstanding throughout.
> > > > 
> > > > QEMU gets fd from opening /dev/kvm_something, uses ioctls (or perhaps
> > > > the fallocate syscall interface itself) to allocate and free the memory,
> > > > ioctl for initializing some of it too.  KVM in control of whether that
> > > > fd can be read or written or mmap'ed or whatever, no need to prevent it
> > > > in shmem.c, no need for flags, seals, notifications to and fro because
> > > > KVM is already in control and knows the history.  If shmem actually has
> > > > value, call into it underneath - somewhat like SysV SHM, and /dev/zero
> > > > mmap, and i915/gem make use of it underneath.  If shmem has nothing to
> > > > add, just allocate and free kernel memory directly, recorded in your
> > > > own xarray.
> > > 
> > > I guess shim layer on top of shmem *can* work. I don't see immediately why
> > > it would not. But I'm not sure it is right direction. We risk creating yet
> > > another parallel VM with own rules/locking/accounting that opaque to
> > > core-mm.
> > 
> > Sorry for necrobumping this thread but I've been reviewing the
> 
> No worries, I'm just stoked someone who actually knows what they're doing is
> chiming in :-)

It's a dangerous business, going out of your subsystem. You step into
code, and if you don't watch your hands, there is no knowing where you
might be swept off to.

That saying goes for me here specifically...

> 
> > memfd_restricted() extension that Ackerley is currently working on. I
> > was pointed to this thread as this is what the extension is building
> > on but I'll reply to both threads here.
> > 
> > From a glance at v10, memfd_restricted() is currently implemented as an
> > in-kernel stacking filesystem. A call to memfd_restricted() creates a
> > new restricted memfd file and a new unlinked tmpfs file and stashes the
> > tmpfs file into the memfd file's private data member. It then uses the
> > tmpfs file's f_ops and i_ops to perform the relevant file and inode
> > operations. So it has the same callstack as a general stacking
> > filesystem like overlayfs in some cases:
> > 
> >         memfd_restricted->getattr()
> >         -> tmpfs->getattr()
> 
> ...
> 
> > Since you're effectively acting like a stacking filesystem you should
> > really use the device number of your memfd restricted filesystem. IOW,
> > sm like:
> > 
> >         stat->dev = memfd_restricted_dentry->d_sb->s_dev;
> > 
> > But then you run into trouble if you want to go forward with Ackerley's
> > extension that allows to explicitly pass in tmpfs fds to
> > memfd_restricted(). Afaict, two tmpfs instances might allocate the same
> > inode number. So now the inode and device number pair isn't unique
> > anymore.
> > 
> > So you might best be served by allocating and reporting your own inode
> > numbers as well.
> > 
> > But if you want to preserve the inode number and device number of the
> > relevant tmpfs instance but still report memfd restricted as your
> > filesystem type
> 
> Unless I missed something along the way, reporting memfd_restricted as a distinct
> filesystem is very much a non-goal.  AFAIK it's purely a side effect of the
> proposed implementation.

In the current implementation you would have to put in effort to fake
this. For example, you would need to also implement ->statfs
super_operation where you'd need to fill in the details of the tmpfs
instance. At that point all that memfd_restricted fs code that you've
written is nothing but deadweight, I would reckon.

> 
> > then I think it's reasonable to ask whether a stacking implementation really
> > makes sense here.
> > 
> > If you extend memfd_restricted() or even consider extending it in the
> > future to take tmpfs file descriptors as arguments to identify the tmpfs
> > instance in which to allocate the underlying tmpfs file for the new
> > restricted memfd file you should really consider a tmpfs based
> > implementation.
> > 
> > Because at that point it just feels like a pointless wrapper to get
> > custom f_ops and i_ops. Plus it's wasteful because you allocate dentries
> > and inodes that you don't really care about at all.
> > 
> > Just off the top of my hat you might be better served:
> > * by a new ioctl() on tmpfs instances that
> >   yield regular tmpfs file descriptors with restricted f_ops and i_ops.
> >   That's not that different from btrfs subvolumes which effectively are
> >   directories but are created through an ioctl().
> 
> I think this is more or less what we want to do, except via a dedicated syscall
> instead of an ioctl() so that the primary interface isn't strictly tied to tmpfs,
> e.g. so that it can be extended to other backing types in the future.

Ok. But just to point this out, this would make memfd_restricted()
a multiplexer on types of memory. And my wild guess is that not all
memory types you might reasonably want to use will have a filesystem
like interface such. So in the future you might end up with multiple
ways of specifying the type of memory:

// use tmpfs backing
memfd_restricted(fd_tmpfs, 0);

// use hugetlbfs backing
memfd_restricted(fd_hugetlbfs, 0);

// use non-fs type memory backing
memfd_restricted(-EBADF, MEMFD_SUPER_FANCY_MEMORY_TYPE);

interface wise I find an unpleasant design. But that multi-memory-open
goal also makes it a bit hard to come up with a clean design (On
possibility would be to use an extensible struct - versioned by size -
similar to openat2() and clone3() such that you can specify all types of
options on the memory in the future.).

> 
> > * by a mount option to tmpfs that makes it act
> >   in this restricted manner then you don't need an ioctl() and can get
> >   away with regular open calls. Such a tmpfs instance would only create
> >   regular, restricted memfds.
> 
> I'd prefer to not go this route, becuase IIUC, it would require relatively invasive
> changes to shmem code, and IIUC would require similar changes to other support
> backings in the future, e.g. hugetlbfs?  And as above, I don't think any of the
> potential use cases need restrictedmem to be a uniquely identifiable mount.

Ok, see my comment above then.

> 
> One of the goals (hopefully not a pipe dream) is to design restrictmem in such a
> way that extending it to support other backing types isn't terribly difficult.

Not necessarily difficult, just difficult to do tastefully imho. But
it's not that has traditionally held people back. ;)

> In case it's not obvious, most of us working on this stuff aren't filesystems
> experts, and many of us aren't mm experts either.  The more we (KVM folks for the
> most part) can leverage existing code to do the heavy lifting, the better.

Well, hopefully we can complement each other's knowledge here.

> 
> After giving myself a bit of a crash course in file systems, would something like
> the below have any chance of (a) working, (b) getting merged, and (c) being
> maintainable?
> 
> The idea is similar to a stacking filesystem, but instead of stacking, restrictedmem
> hijacks a f_ops and a_ops to create a lightweight shim around tmpfs.  There are
> undoubtedly issues and edge cases, I'm just looking for a quick "yes, this might
> be doable" or a "no, that's absolutely bonkers, don't try it".

Maybe, but I think it's weird. _Replacing_ f_ops isn't something that's
unprecedented. It happens everytime a character device is opened (see
fs/char_dev.c:chrdev_open()). And debugfs does a similar (much more
involved) thing where it replaces it's proxy f_ops with the relevant
subsystem's f_ops. The difference is that in both cases the replace
happens at ->open() time; and the replace is done once. Afterwards only
the newly added f_ops are relevant.

In your case you'd be keeping two sets of {f,a}_ops; one usable by
userspace and another only usable by in-kernel consumers. And there are
some concerns (non-exhaustive list), I think:

* {f,a}_ops weren't designed for this. IOW, one set of {f,a}_ops is
  authoritative per @file and it is left to the individual subsystems to
  maintain driver specific ops (see the sunrpc stuff or sockets).
* lifetime management for the two sets of {f,a}_ops: If the ops belong
  to a module then you need to make sure that the module can't get
  unloaded while you're using the fops. Might not be a concern in this
  case.
* brittleness: Not all f_ops for example deal with userspace
  functionality some deal with cleanup when the file is closed like
  ->release(). So it's delicate to override that functionality with
  custom f_ops. Restricted memfds could easily forget to cleanup
  resources.
* Potential for confusion why there's two sets of {f,a}_ops.
* f_ops specifically are generic across a vast amount of consumers and
  are subject to change. If memfd_restricted() has specific requirements
  because of this weird double-use they won't be taken into account.

I find this hard to navigate tbh and it feels like taking a shortcut to
avoid building a proper api. If you only care about a specific set of
operations specific to memfd restricte that needs to be available to
in-kernel consumers, I wonder if you shouldn't just go one step further
then your proposal below and build a dedicated minimal ops api. Idk,
sketching like a madman on a drawning board here with no claim to
feasibility from a mm perspective whatsoever:

struct restrictedmem_ops {
	// only contains very limited stuff you need or special stuff
	// you nee, similar to struct proto_ops (sockets) and so on
};

struct restrictedmem {
	const struct restrictedmem_ops ops;
};

This would avoid fuzzing with two different set of {f,a}_ops in this
brittle way. It would force you to clarify the semantics that you need
and the operations that you need or don't need implemented. And it would
get rid of the ambiguity inherent to using two sets of {f,a}_ops.

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Sean Christopherson]

On Wed, Apr 19, 2023, Christian Brauner wrote:
> On Thu, Apr 13, 2023 at 03:28:43PM -0700, Sean Christopherson wrote:
> > > But if you want to preserve the inode number and device number of the
> > > relevant tmpfs instance but still report memfd restricted as your
> > > filesystem type
> > 
> > Unless I missed something along the way, reporting memfd_restricted as a distinct
> > filesystem is very much a non-goal.  AFAIK it's purely a side effect of the
> > proposed implementation.
> 
> In the current implementation you would have to put in effort to fake
> this. For example, you would need to also implement ->statfs
> super_operation where you'd need to fill in the details of the tmpfs
> instance. At that point all that memfd_restricted fs code that you've
> written is nothing but deadweight, I would reckon.

After digging a bit, I suspect the main reason Kirill implemented an overlay to
inode_operations was to prevent modifying the file size via ->setattr().  Relying
on shmem_setattr() to unmap entries in KVM's MMU wouldn't work because, by design,
the memory can't be mmap()'d into host userspace. 

	if (attr->ia_valid & ATTR_SIZE) {
		if (memfd->f_inode->i_size)
			return -EPERM;

		if (!PAGE_ALIGNED(attr->ia_size))
			return -EINVAL;	
	}

But I think we can solve this particular problem by using F_SEAL_{GROW,SHRINK} or
SHMEM_LONGPIN.  For a variety of reasons, I'm leaning more and more toward making
this a KVM ioctl() instead of a dedicated syscall, at which point we can be both
more flexible and more draconian, e.g. let userspace provide the file size at the
time of creation, but make the size immutable, at least by default.

> > After giving myself a bit of a crash course in file systems, would something like
> > the below have any chance of (a) working, (b) getting merged, and (c) being
> > maintainable?
> > 
> > The idea is similar to a stacking filesystem, but instead of stacking, restrictedmem
> > hijacks a f_ops and a_ops to create a lightweight shim around tmpfs.  There are
> > undoubtedly issues and edge cases, I'm just looking for a quick "yes, this might
> > be doable" or a "no, that's absolutely bonkers, don't try it".
> 
> Maybe, but I think it's weird.

Yeah, agreed.

> _Replacing_ f_ops isn't something that's unprecedented. It happens everytime
> a character device is opened (see fs/char_dev.c:chrdev_open()). And debugfs
> does a similar (much more involved) thing where it replaces it's proxy f_ops
> with the relevant subsystem's f_ops. The difference is that in both cases the
> replace happens at ->open() time; and the replace is done once. Afterwards
> only the newly added f_ops are relevant.
> 
> In your case you'd be keeping two sets of {f,a}_ops; one usable by
> userspace and another only usable by in-kernel consumers. And there are
> some concerns (non-exhaustive list), I think:
> 
> * {f,a}_ops weren't designed for this. IOW, one set of {f,a}_ops is
>   authoritative per @file and it is left to the individual subsystems to
>   maintain driver specific ops (see the sunrpc stuff or sockets).
> * lifetime management for the two sets of {f,a}_ops: If the ops belong
>   to a module then you need to make sure that the module can't get
>   unloaded while you're using the fops. Might not be a concern in this
>   case.

Ah, whereas I assume the owner of inode_operations is pinned by ??? (dentry?)
holding a reference to the inode?

> * brittleness: Not all f_ops for example deal with userspace
>   functionality some deal with cleanup when the file is closed like
>   ->release(). So it's delicate to override that functionality with
>   custom f_ops. Restricted memfds could easily forget to cleanup
>   resources.
> * Potential for confusion why there's two sets of {f,a}_ops.
> * f_ops specifically are generic across a vast amount of consumers and
>   are subject to change. If memfd_restricted() has specific requirements
>   because of this weird double-use they won't be taken into account.
> 
> I find this hard to navigate tbh and it feels like taking a shortcut to
> avoid building a proper api.

Agreed.  At the very least, it would be better to take an explicit dependency on
whatever APIs are being used instead of somewhat blindly bouncing through ->fallocate().
I think that gives us a clearer path to getting something merged too, as we'll
need Acks on making specific functions visible, i.e. will give MM maintainers
something concrete to react too.

> If you only care about a specific set of operations specific to memfd
> restricte that needs to be available to in-kernel consumers, I wonder if you
> shouldn't just go one step further then your proposal below and build a
> dedicated minimal ops api.

This is actually very doable for shmem.  Unless I'm missing something, because
our use case doesn't allow mmap(), swap, or migration, a good chunk of
shmem_fallocate() is simply irrelevant.  The result is only ~100 lines of code,
and quite straightforward.

My biggest concern, outside of missing a detail in shmem, is adding support for
HugeTLBFS, which is likely going to be requested/needed sooner than later.  At a
glance, hugetlbfs_fallocate() is quite a bit more complex, i.e. not something I'm
keen to duplicate.  But that's also a future problem to some extent, as it's
purely kernel internals; the uAPI side of things doesn't seem like it'll be messy
at all.

Thanks again!

Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Christian Brauner]

On Wed, Apr 19, 2023 at 05:49:55PM -0700, Sean Christopherson wrote:
> On Wed, Apr 19, 2023, Christian Brauner wrote:
> > On Thu, Apr 13, 2023 at 03:28:43PM -0700, Sean Christopherson wrote:
> > > > But if you want to preserve the inode number and device number of the
> > > > relevant tmpfs instance but still report memfd restricted as your
> > > > filesystem type
> > > 
> > > Unless I missed something along the way, reporting memfd_restricted as a distinct
> > > filesystem is very much a non-goal.  AFAIK it's purely a side effect of the
> > > proposed implementation.
> > 
> > In the current implementation you would have to put in effort to fake
> > this. For example, you would need to also implement ->statfs
> > super_operation where you'd need to fill in the details of the tmpfs
> > instance. At that point all that memfd_restricted fs code that you've
> > written is nothing but deadweight, I would reckon.
> 
> After digging a bit, I suspect the main reason Kirill implemented an overlay to
> inode_operations was to prevent modifying the file size via ->setattr().  Relying
> on shmem_setattr() to unmap entries in KVM's MMU wouldn't work because, by design,
> the memory can't be mmap()'d into host userspace. 
> 
> 	if (attr->ia_valid & ATTR_SIZE) {
> 		if (memfd->f_inode->i_size)
> 			return -EPERM;
> 
> 		if (!PAGE_ALIGNED(attr->ia_size))
> 			return -EINVAL;	
> 	}
> 
> But I think we can solve this particular problem by using F_SEAL_{GROW,SHRINK} or
> SHMEM_LONGPIN.  For a variety of reasons, I'm leaning more and more toward making
> this a KVM ioctl() instead of a dedicated syscall, at which point we can be both
> more flexible and more draconian, e.g. let userspace provide the file size at the
> time of creation, but make the size immutable, at least by default.
> 
> > > After giving myself a bit of a crash course in file systems, would something like
> > > the below have any chance of (a) working, (b) getting merged, and (c) being
> > > maintainable?
> > > 
> > > The idea is similar to a stacking filesystem, but instead of stacking, restrictedmem
> > > hijacks a f_ops and a_ops to create a lightweight shim around tmpfs.  There are
> > > undoubtedly issues and edge cases, I'm just looking for a quick "yes, this might
> > > be doable" or a "no, that's absolutely bonkers, don't try it".
> > 
> > Maybe, but I think it's weird.
> 
> Yeah, agreed.
> 
> > _Replacing_ f_ops isn't something that's unprecedented. It happens everytime
> > a character device is opened (see fs/char_dev.c:chrdev_open()). And debugfs
> > does a similar (much more involved) thing where it replaces it's proxy f_ops
> > with the relevant subsystem's f_ops. The difference is that in both cases the
> > replace happens at ->open() time; and the replace is done once. Afterwards
> > only the newly added f_ops are relevant.
> > 
> > In your case you'd be keeping two sets of {f,a}_ops; one usable by
> > userspace and another only usable by in-kernel consumers. And there are
> > some concerns (non-exhaustive list), I think:
> > 
> > * {f,a}_ops weren't designed for this. IOW, one set of {f,a}_ops is
> >   authoritative per @file and it is left to the individual subsystems to
> >   maintain driver specific ops (see the sunrpc stuff or sockets).
> > * lifetime management for the two sets of {f,a}_ops: If the ops belong
> >   to a module then you need to make sure that the module can't get
> >   unloaded while you're using the fops. Might not be a concern in this
> >   case.
> 
> Ah, whereas I assume the owner of inode_operations is pinned by ??? (dentry?)
> holding a reference to the inode?

I don't think it would be possible to safely replace inode_operations
after the inode's been made visible in caches.

It works with file_operations because when a file is opened a new struct
file is allocated which isn't reachable anywhere before fd_install() is
called. So it is possible to replace f_ops in the default
f->f_op->open() method (which is what devices do as the inode is located
on e.g., ext4/xfs/tmpfs but the functionality of the device usually
provided by some driver/module through its file_operations). The default
f_ops are taken from i_fop of the inode.

The lifetime of the file_/inode_operations will be aligned with the
lifetime of the module they're originating from. If only
file_/inode_operations are used from within the same module then there
should never be any lifetime concerns.

So an inode doesn't explictly pin file_/inode_operations because there's
usually no need to do that and it be weird if each new inode would take
a reference on the f_ops/i_ops on the off-chance that someone _might_
open the file. Let alone the overhead of calling try_module_get()
everytime a new inode is added to the cache. There are various fs
objects - the superblock which is pinning the filesystem/module - that
exceed the lifetime of inodes and dentries. Both also may be dropped
from their respective caches and readded later.

Pinning of the module for f_ops is done because it is possible that some
filesystem/driver might want to use the file_operations of some other
filesystem/driver by default and they are in separate modules. So the
fops_get() in do_dentry_open is there because it's not guaranteed that
file_/inode_operations originate from the same module as the inode
that's opened. If the module is still alive during the open then a
reference to its f_ops is taken if not then the open will fail with
ENODEV.

That's to the best of my knowledge.

> 
> > * brittleness: Not all f_ops for example deal with userspace
> >   functionality some deal with cleanup when the file is closed like
> >   ->release(). So it's delicate to override that functionality with
> >   custom f_ops. Restricted memfds could easily forget to cleanup
> >   resources.
> > * Potential for confusion why there's two sets of {f,a}_ops.
> > * f_ops specifically are generic across a vast amount of consumers and
> >   are subject to change. If memfd_restricted() has specific requirements
> >   because of this weird double-use they won't be taken into account.
> > 
> > I find this hard to navigate tbh and it feels like taking a shortcut to
> > avoid building a proper api.
> 
> Agreed.  At the very least, it would be better to take an explicit dependency on
> whatever APIs are being used instead of somewhat blindly bouncing through ->fallocate().
> I think that gives us a clearer path to getting something merged too, as we'll
> need Acks on making specific functions visible, i.e. will give MM maintainers
> something concrete to react too.
> 
> > If you only care about a specific set of operations specific to memfd
> > restricte that needs to be available to in-kernel consumers, I wonder if you
> > shouldn't just go one step further then your proposal below and build a
> > dedicated minimal ops api.
> 
> This is actually very doable for shmem.  Unless I'm missing something, because
> our use case doesn't allow mmap(), swap, or migration, a good chunk of
> shmem_fallocate() is simply irrelevant.  The result is only ~100 lines of code,
> and quite straightforward.
> 
> My biggest concern, outside of missing a detail in shmem, is adding support for
> HugeTLBFS, which is likely going to be requested/needed sooner than later.  At a
> glance, hugetlbfs_fallocate() is quite a bit more complex, i.e. not something I'm
> keen to duplicate.  But that's also a future problem to some extent, as it's
> purely kernel internals; the uAPI side of things doesn't seem like it'll be messy
> at all.
> 
> Thanks again!

Sure thing.

Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

[Sean Christopherson]

On Tue, Apr 18, 2023, Ackerley Tng wrote:
> Sean Christopherson <seanjc@google.com> writes:
> > I agree, a pure alignment check is too restrictive, and not really what I
> > intended despite past me literally saying that's what I wanted :-)  I think
> > I may have also inverted the "less alignment" statement, but luckily I
> > believe that ends up being a moot point.
> 
> > The goal is to avoid having to juggle scenarios where KVM wants to create a
> > hugepage, but restrictedmem can't provide one because of a misaligned file
> > offset.  I think the rule we want is that the offset must be aligned to the
> > largest page size allowed by the memslot _size_.  E.g. on x86, if the
> > memslot size is >=1GiB then the offset must be 1GiB or beter, ditto for
> > >=2MiB and >=4KiB (ignoring that 4KiB is already a requirement).
> 
> > We could loosen that to say the largest size allowed by the memslot, but I
> > don't think that's worth the effort unless it's trivially easy to implement
> > in code, e.g. KVM could technically allow a 4KiB aligned offset if the
> > memslot is 2MiB sized but only 4KiB aligned on the GPA.  I doubt there's a
> > real use case for such a memslot, so I want to disallow that unless it's
> > super easy to implement.
> 
> Checking my understanding here about why we need this alignment check:
> 
> When KVM requests a page from restrictedmem, KVM will provide an offset
> into the file in terms of 4K pages.
> 
> When shmem is configured to use hugepages, shmem_get_folio() will round
> the requested offset down to the nearest hugepage-aligned boundary in
> shmem_alloc_hugefolio().
> 
> Example of problematic configuration provided to
> KVM_SET_USER_MEMORY_REGION2:
> 
> + shmem configured to use 1GB pages
> + restrictedmem_offset provided to KVM_SET_USER_MEMORY_REGION2: 0x4000
> + memory_size provided in KVM_SET_USER_MEMORY_REGION2: 1GB
> + KVM requests offset (pgoff_t) 0x8, which translates to offset 0x8000
> 
> restrictedmem_get_page() and shmem_get_folio() returns the page for
> offset 0x0 in the file, since rounding down 0x8000 to the nearest 1GB is
> 0x0. This is allocating outside the range that KVM is supposed to use,
> since the parameters provided in KVM_SET_USER_MEMORY_REGION2 is only
> supposed to be offset 0x4000 to (0x4000 + 1GB = 0x40004000) in the file.
> 
> IIUC shmem will actually just round down (0x4000 rounded down to nearest
> 1GB will be 0x0) and allocate without checking bounds, so if offset 0x0
> to 0x4000 in the file were supposed to be used by something else, there
> might be issues.
> 
> Hence, this alignment check ensures that rounding down of any offsets
> provided by KVM (based on page size configured in the backing file
> provided) to restrictedmem_get_page() must not go below the offset
> provided to KVM_SET_USER_MEMORY_REGION2.
> 
> Enforcing alignment of restrictedmem_offset based on the currently-set
> page size in the backing file (i.e. shmem) may not be effective, since
> the size of the pages in the backing file can be adjusted to a larger
> size after KVM_SET_USER_MEMORY_REGION2 succeeds. With that, we may still
> end up allocating outside the range that KVM was provided with.
> 
> Hence, to be safe, we should check alignment to the max page size across
> all backing filesystems, so the constraint is
> 
>     rounding down restrictedmem_offset to
>     min(max page size across all backing filesystems,
>         max page size that fits in memory_size) == restrictedmem_offset
> 
> which is the same check as
> 
>     restrictedmem_offset must be aligned to min(max page size across all
>     backing filesystems, max page size that fits in memory_size)
> 
> which can safely reduce to
> 
>     restrictedmem_offset must be aligned to max page size that fits in
>     memory_size
> 
> since "max page size that fits in memory_size" is probably <= to "max
> page size across all backing filesystems", and if it's larger, it'll
> just be a tighter constraint.

Yes?  The alignment check isn't strictly required, KVM _could_ deal with the above
scenario, it's just a lot simpler and safer for KVM if the file offset needs to
be sanely aligned.

> If the above understanding is correct:
> 
> + We must enforce this in the KVM_SET_USER_MEMORY_REGION2 handler, since
>   IIUC shmem will just round down and allocate without checking bounds.
> 
>     + I think this is okay because holes in the restrictedmem file (in
>       terms of offset) made to accommodate this constraint don't cost us
>       anything anyway(?) Are they just arbitrary offsets in a file? In
>       our case, this file is usually a new and empty file.
> 
>     + In the case of migration of a restrictedmem file between two KVM
>       VMs, this constraint would cause a problem is if the largest
>       possible page size on the destination machine is larger than that
>       of the source machine. In that case, we might have to move the
>       data in the file to a different offset (a separate problem).

Hmm, I was thinking this would be a non-issue because the check would be tied to
the max page _possible_ page size irrespective of hardware support, but that would
be problematic if KVM ever supports 512GiB pages.  I'm not sure that speculatively
requiring super huge memslots to be 512GiB aligned is sensible.

Aha!  If we go with a KVM ioctl(), a clean way around this is tie the alignment
requirement to the memfd flags, e.g. if userspace requests the memfd to be backed
by PMD hugepages, then the memslot offset needs to be 2MiB aligned on x86.  That
will continue to work if (big if) KVM supports 512GiB pages because the "legacy"
memfd would still be capped at 2MiB pages.

Architectures that support variable hugepage sizes might need to do something
else, but I don't think that possibility affects what x86 can/can't do.

> + On this note, it seems like there is no check for when the range is
>   smaller than the allocated page? Like if the range provided is 4KB in
>   size, but shmem is then configured to use a 1GB page, will we end up
>   allocating past the end of the range?

No, KVM already gracefully handles situations like this.  Well, x86 does, I assume
other architectures do too :-)

As above, the intent of the extra restriction is so that KVM doen't need even more
weird code (read: math) to gracefully handle the new edge cases that would come with
fd-only memslots.

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Nicolas Saenz Julienne]

Hi,

On Fri Dec 2, 2022 at 6:13 AM UTC, Chao Peng wrote:

[...]

> +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: u64 memory attributes bitmask(out)
> +:Returns: 0 on success, <0 on error
> +
> +Returns supported memory attributes bitmask. Supported memory attributes will
> +have the corresponding bits set in u64 memory attributes bitmask.
> +
> +The following memory attributes are defined::
> +
> +  #define KVM_MEMORY_ATTRIBUTE_READ              (1ULL << 0)
> +  #define KVM_MEMORY_ATTRIBUTE_WRITE             (1ULL << 1)
> +  #define KVM_MEMORY_ATTRIBUTE_EXECUTE           (1ULL << 2)
> +  #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
> +
> +4.139 KVM_SET_MEMORY_ATTRIBUTES
> +-----------------------------------------
> +
> +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> +:Architectures: x86
> +:Type: vm ioctl
> +:Parameters: struct kvm_memory_attributes(in/out)
> +:Returns: 0 on success, <0 on error
> +
> +Sets memory attributes for pages in a guest memory range. Parameters are
> +specified via the following structure::
> +
> +  struct kvm_memory_attributes {
> +	__u64 address;
> +	__u64 size;
> +	__u64 attributes;
> +	__u64 flags;
> +  };
> +
> +The user sets the per-page memory attributes to a guest memory range indicated
> +by address/size, and in return KVM adjusts address and size to reflect the
> +actual pages of the memory range have been successfully set to the attributes.
> +If the call returns 0, "address" is updated to the last successful address + 1
> +and "size" is updated to the remaining address size that has not been set
> +successfully. The user should check the return value as well as the size to
> +decide if the operation succeeded for the whole range or not. The user may want
> +to retry the operation with the returned address/size if the previous range was
> +partially successful.
> +
> +Both address and size should be page aligned and the supported attributes can be
> +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> +
> +The "flags" field may be used for future extensions and should be set to 0s.

We have been looking into adding support for the Hyper-V VSM extensions
which Windows uses to implement Credential Guard. This interface seems
like a good fit for one of its underlying features. I just wanted to
share a bit about it, and see if we can expand it to fit this use-case.
Note that this was already briefly discussed between Sean and Alex some
time ago[1].

VSM introduces isolated guest execution contexts called Virtual Trust
Levels (VTL) [2]. Each VTL has its own memory access protections,
virtual processors states, interrupt controllers and overlay pages. VTLs
are hierarchical and might enforce memory protections on less privileged
VTLs. Memory protections are enforced on a per-GPA granularity.

The list of possible protections is:
- No access -- This needs a new memory attribute, I think.
- Read-only, no execute
- Read-only, execute
- Read/write, no execute
- Read/write, execute

We implemented this in the past by using a separate address space per
VTL and updating memory regions on protection changes. But having to
update the memory slot layout for every permission change scales poorly,
especially as we have to perform 100.000s of these operations at boot
(see [1] for a little more context).

I believe the biggest barrier for us to use memory attributes is not
having the ability to target specific address spaces, or to the very
least having some mechanism to maintain multiple independent layers of
attributes.

Also sorry for not posting our VSM patches. They are not ready for
upstream review yet, but we're working on it.

Nicolas

[1] https://patchwork.kernel.org/comment/25054908/
[2] See Chapter 15 of Microsoft's 'Hypervisor Top Level Functional Specification':
    https://raw.githubusercontent.com/MicrosoftDocs/Virtualization-Documentation/main/tlfs/Hypervisor%20Top%20Level%20Functional%20Specification%20v6.0b.pdf

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Fri, May 19, 2023, Nicolas Saenz Julienne wrote:
> Hi,
> 
> On Fri Dec 2, 2022 at 6:13 AM UTC, Chao Peng wrote:
> 
> [...]
> > +The user sets the per-page memory attributes to a guest memory range indicated
> > +by address/size, and in return KVM adjusts address and size to reflect the
> > +actual pages of the memory range have been successfully set to the attributes.
> > +If the call returns 0, "address" is updated to the last successful address + 1
> > +and "size" is updated to the remaining address size that has not been set
> > +successfully. The user should check the return value as well as the size to
> > +decide if the operation succeeded for the whole range or not. The user may want
> > +to retry the operation with the returned address/size if the previous range was
> > +partially successful.
> > +
> > +Both address and size should be page aligned and the supported attributes can be
> > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> > +
> > +The "flags" field may be used for future extensions and should be set to 0s.
> 
> We have been looking into adding support for the Hyper-V VSM extensions
> which Windows uses to implement Credential Guard. This interface seems
> like a good fit for one of its underlying features. I just wanted to
> share a bit about it, and see if we can expand it to fit this use-case.
> Note that this was already briefly discussed between Sean and Alex some
> time ago[1].
> 
> VSM introduces isolated guest execution contexts called Virtual Trust
> Levels (VTL) [2]. Each VTL has its own memory access protections,
> virtual processors states, interrupt controllers and overlay pages. VTLs
> are hierarchical and might enforce memory protections on less privileged
> VTLs. Memory protections are enforced on a per-GPA granularity.
> 
> The list of possible protections is:
> - No access -- This needs a new memory attribute, I think.

No, if KVM provides three bits for READ, WRITE, and EXECUTE, then userspace can
get all the possible combinations.  E.g. this is RWX=000b

> - Read-only, no execute

RWX=100b (using my completely arbitrary ordering of RWX bits :-) )

> - Read-only, execute

RWX=101b

> - Read/write, no execute

RWX=110b

> - Read/write, execute

RWX=111b

> We implemented this in the past by using a separate address space per
> VTL and updating memory regions on protection changes. But having to
> update the memory slot layout for every permission change scales poorly,
> especially as we have to perform 100.000s of these operations at boot
> (see [1] for a little more context).
> 
> I believe the biggest barrier for us to use memory attributes is not
> having the ability to target specific address spaces, or to the very
> least having some mechanism to maintain multiple independent layers of
> attributes.

Can you elaborate on "specific address spaces"?  In KVM, that usually means SMM,
but the VTL comment above makes me think you're talking about something entirely
different.  E.g. can you provide a brief summary of the requirements/expectations?

> Also sorry for not posting our VSM patches. They are not ready for
> upstream review yet, but we're working on it.
> 
> Nicolas
> 
> [1] https://patchwork.kernel.org/comment/25054908/
> [2] See Chapter 15 of Microsoft's 'Hypervisor Top Level Functional Specification':
>     https://raw.githubusercontent.com/MicrosoftDocs/Virtualization-Documentation/main/tlfs/Hypervisor%20Top%20Level%20Functional%20Specification%20v6.0b.pdf

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Nicolas Saenz Julienne]

Hi Sean,

On Fri May 19, 2023 at 6:23 PM UTC, Sean Christopherson wrote:
> On Fri, May 19, 2023, Nicolas Saenz Julienne wrote:
> > Hi,
> >
> > On Fri Dec 2, 2022 at 6:13 AM UTC, Chao Peng wrote:
> >
> > [...]
> > > +The user sets the per-page memory attributes to a guest memory range indicated
> > > +by address/size, and in return KVM adjusts address and size to reflect the
> > > +actual pages of the memory range have been successfully set to the attributes.
> > > +If the call returns 0, "address" is updated to the last successful address + 1
> > > +and "size" is updated to the remaining address size that has not been set
> > > +successfully. The user should check the return value as well as the size to
> > > +decide if the operation succeeded for the whole range or not. The user may want
> > > +to retry the operation with the returned address/size if the previous range was
> > > +partially successful.
> > > +
> > > +Both address and size should be page aligned and the supported attributes can be
> > > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> > > +
> > > +The "flags" field may be used for future extensions and should be set to 0s.
> >
> > We have been looking into adding support for the Hyper-V VSM extensions
> > which Windows uses to implement Credential Guard. This interface seems
> > like a good fit for one of its underlying features. I just wanted to
> > share a bit about it, and see if we can expand it to fit this use-case.
> > Note that this was already briefly discussed between Sean and Alex some
> > time ago[1].
> >
> > VSM introduces isolated guest execution contexts called Virtual Trust
> > Levels (VTL) [2]. Each VTL has its own memory access protections,
> > virtual processors states, interrupt controllers and overlay pages. VTLs
> > are hierarchical and might enforce memory protections on less privileged
> > VTLs. Memory protections are enforced on a per-GPA granularity.
> >
> > The list of possible protections is:
> > - No access -- This needs a new memory attribute, I think.
>
> No, if KVM provides three bits for READ, WRITE, and EXECUTE, then userspace can
> get all the possible combinations.  E.g. this is RWX=000b

That's not what the current implementation does, when attributes is
equal 0 it clears the entries from the xarray:

static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
					   struct kvm_memory_attributes *attrs)
{

    entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
[...]
    for (i = start; i < end; i++)
    	if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
    			    GFP_KERNEL_ACCOUNT)))
        		break;
}

From Documentation/core-api/xarray.rst:

"There is no difference between an entry that has never
been stored to, one that has been erased and one that has most recently
had ``NULL`` stored to it."

The way I understood the series, there needs to be a differentiation
between no attributes (regular page fault) and no-access.

> > We implemented this in the past by using a separate address space per
> > VTL and updating memory regions on protection changes. But having to
> > update the memory slot layout for every permission change scales poorly,
> > especially as we have to perform 100.000s of these operations at boot
> > (see [1] for a little more context).
> >
> > I believe the biggest barrier for us to use memory attributes is not
> > having the ability to target specific address spaces, or to the very
> > least having some mechanism to maintain multiple independent layers of
> > attributes.
>
> Can you elaborate on "specific address spaces"?  In KVM, that usually means SMM,
> but the VTL comment above makes me think you're talking about something entirely
> different.  E.g. can you provide a brief summary of the requirements/expectations?

I'll do so with a clear head on Monday. :)

Thanks!
Nicolas

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Fri, May 19, 2023, Nicolas Saenz Julienne wrote:
> Hi Sean,
> 
> On Fri May 19, 2023 at 6:23 PM UTC, Sean Christopherson wrote:
> > On Fri, May 19, 2023, Nicolas Saenz Julienne wrote:
> > > Hi,
> > >
> > > On Fri Dec 2, 2022 at 6:13 AM UTC, Chao Peng wrote:
> > >
> > > [...]
> > > > +The user sets the per-page memory attributes to a guest memory range indicated
> > > > +by address/size, and in return KVM adjusts address and size to reflect the
> > > > +actual pages of the memory range have been successfully set to the attributes.
> > > > +If the call returns 0, "address" is updated to the last successful address + 1
> > > > +and "size" is updated to the remaining address size that has not been set
> > > > +successfully. The user should check the return value as well as the size to
> > > > +decide if the operation succeeded for the whole range or not. The user may want
> > > > +to retry the operation with the returned address/size if the previous range was
> > > > +partially successful.
> > > > +
> > > > +Both address and size should be page aligned and the supported attributes can be
> > > > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> > > > +
> > > > +The "flags" field may be used for future extensions and should be set to 0s.
> > >
> > > We have been looking into adding support for the Hyper-V VSM extensions
> > > which Windows uses to implement Credential Guard. This interface seems
> > > like a good fit for one of its underlying features. I just wanted to
> > > share a bit about it, and see if we can expand it to fit this use-case.
> > > Note that this was already briefly discussed between Sean and Alex some
> > > time ago[1].
> > >
> > > VSM introduces isolated guest execution contexts called Virtual Trust
> > > Levels (VTL) [2]. Each VTL has its own memory access protections,
> > > virtual processors states, interrupt controllers and overlay pages. VTLs
> > > are hierarchical and might enforce memory protections on less privileged
> > > VTLs. Memory protections are enforced on a per-GPA granularity.
> > >
> > > The list of possible protections is:
> > > - No access -- This needs a new memory attribute, I think.
> >
> > No, if KVM provides three bits for READ, WRITE, and EXECUTE, then userspace can
> > get all the possible combinations.  E.g. this is RWX=000b
> 
> That's not what the current implementation does, when attributes is
> equal 0 it clears the entries from the xarray:
> 
> static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> 					   struct kvm_memory_attributes *attrs)
> {
> 
>     entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> [...]
>     for (i = start; i < end; i++)
>     	if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
>     			    GFP_KERNEL_ACCOUNT)))
>         		break;
> }
> 
> >From Documentation/core-api/xarray.rst:
> 
> "There is no difference between an entry that has never
> been stored to, one that has been erased and one that has most recently
> had ``NULL`` stored to it."
> 
> The way I understood the series, there needs to be a differentiation
> between no attributes (regular page fault) and no-access.

Ah, I see what you're saying.  There are multiple ways to solve things without a
"no access" flag while still maintaining an empty xarray for the default case.
E.g. invert the flags to be DENY flags[*], have an internal-only "entry valid" flag,
etc.

[*] I vaguely recall suggesting a "deny" approach somewhere, but I may just be
    making things up to make it look like I thought deeply about this ;-)

Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Nicolas Saenz Julienne]

Hi Sean,

On Fri May 19, 2023 at 6:23 PM UTC, Sean Christopherson wrote:
> On Fri, May 19, 2023, Nicolas Saenz Julienne wrote:
> > Hi,
> > On Fri Dec 2, 2022 at 6:13 AM UTC, Chao Peng wrote:

[...]

> > VSM introduces isolated guest execution contexts called Virtual Trust
> > Levels (VTL) [2]. Each VTL has its own memory access protections,
> > virtual processors states, interrupt controllers and overlay pages. VTLs
> > are hierarchical and might enforce memory protections on less privileged
> > VTLs. Memory protections are enforced on a per-GPA granularity.
> >
> > We implemented this in the past by using a separate address space per
> > VTL and updating memory regions on protection changes. But having to
> > update the memory slot layout for every permission change scales poorly,
> > especially as we have to perform 100.000s of these operations at boot
> > (see [1] for a little more context).
> >
> > I believe the biggest barrier for us to use memory attributes is not
> > having the ability to target specific address spaces, or to the very
> > least having some mechanism to maintain multiple independent layers of
> > attributes.
>
> Can you elaborate on "specific address spaces"?  In KVM, that usually means SMM,
> but the VTL comment above makes me think you're talking about something entirely
> different.  E.g. can you provide a brief summary of the requirements/expectations?

Let me refresh some concepts first. VTLs are vCPU modes implemented by
the hypervisor. Lower VTLs switch into higher VTLs [1] through a
hypercall or asynchronously through interrupts. Each VTL has its own CPU
architectural state, lapic and MSR state (applies to only some MSRs).
These are saved/restored when switching VTLS [2]. Additionally, VTLs
share a common GPA->HPA mapping, but protection bits differ depending on
which VTL the CPU is on. Privileged VTLs might revoke R/W/X(+MBEC,
optional) access bits from lower VTLs on a per-GPA basis.

In order to deal with the per-VTL memory protection bits, we extended
the number of KVM address spaces and assigned one to each VTL. The
hypervisor initializes all VTLs address spaces with the same mappings
and protections, they are expected to diverge during runtime. Operations
that rely on memory slots for GPA->HPA/HVA translations (including page
faults) are already address space aware, so adding VTL support was
fairly simple.

Ultimately, when a privileged VTL enforces memory protections on lower
VTLs we update that VTL's address space memory regions to reflect them.
Protection changes are requested through a hypercall, which expects the
new protection to be visible system wide upon returning from it. These
hypercalls happen around 100000+ times during boot, so we introduced an
"atomic memory slot update" API similar to Emanuele's [3] that allows
splitting memory regions/changing permissions concurrent with other
vCPUs.

Now, if we had a way to map memory attributes to specific VTLs, we could
use that instead. Actually, we wouldn't need to extend address spaces at
all to support this (we might still need them to support Overlay Pages,
but that's another story).

Hope it makes a little more sense now. :)

Nicolas

[1] In practice we've only seen VTL0 and VTL1 being used. The spec
    supports up to 16 VTLs.

[2] One can draw an analogy with arm's TrustZone. The hypervisor plays
    the role of EL3. Windows (VTL0) runs in Non-Secure (EL0/EL1) and the
    secure kernel (VTL1) in Secure World (EL1s/EL0s).

[3] https://lore.kernel.org/all/20220909104506.738478-1-eesposit@redhat.com/