[PATCH v7 09/14] KVM: Extend the memslot to support fd-based private memory

Chao Peng
2022-07-06T08:26:35Z

Extend the memslot definition to provide guest private memory through a
file descriptor(fd) instead of userspace_addr(hva). Such guest private
memory(fd) may never be mapped into userspace so no userspace_addr(hva)
can be used. Instead add another two new fields
(private_fd/private_offset), plus the existing memory_size to represent
the private memory range. Such memslot can still have the existing
userspace_addr(hva). When use, a single memslot can maintain both
private memory through private fd(private_fd/private_offset) and shared
memory through hva(userspace_addr). Whether the private or shared part
is effective for a guest GPA is maintained by other KVM code.

Since there is no userspace mapping for private fd so we cannot
rely on get_user_pages() to get the pfn in KVM, instead we add a new
memfile_notifier in the memslot and rely on it to get pfn by interacting
the callbacks from memory backing store with the fd/offset.

This new extension is indicated by a new flag KVM_MEM_PRIVATE. At
compile time, a new config HAVE_KVM_PRIVATE_MEM is added and right now
it is selected on X86_64 for Intel TDX usage.

To make KVM easy, internally we 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>
---
Documentation/virt/kvm/api.rst | 38 ++++++++++++++++----
arch/x86/kvm/Kconfig | 2 ++
arch/x86/kvm/x86.c | 2 +-
include/linux/kvm_host.h | 13 +++++--
include/uapi/linux/kvm.h | 28 +++++++++++++++
virt/kvm/Kconfig | 3 ++
virt/kvm/kvm_main.c | 64 +++++++++++++++++++++++++++++-----
7 files changed, 132 insertions(+), 18 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index bafaeedd455c..4f27c973a952 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 private_offset;
+ __u32 private_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 +1374,27 @@ 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 includes all the kvm_userspace_memory_region
+fields. It also includes additional fields for some specific 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 below flags:
+
+- KVM_MEM_LOG_DIRTY_PAGES 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.
+
+- KVM_MEM_READONLY 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_MEM_PRIVATE can be set to indicate a new slot has private memory backed by
+ a file descirptor(fd) and the content of the private memory is invisible to
+ userspace. In this case, userspace should use private_fd/private_offset in
+ kvm_userspace_memory_region_ext to instruct KVM to provide private memory to
+ guest. Userspace should guarantee not to map the same pfn indicated by
+ private_fd/private_offset to different gfns with 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 e3cbd7706136..1f160801e2a7 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -48,6 +48,8 @@ config KVM
select SRCU
select INTERVAL_TREE
select HAVE_KVM_PM_NOTIFIER if PM
+ select HAVE_KVM_PRIVATE_MEM if X86_64
+ select MEMFILE_NOTIFIER if HAVE_KVM_PRIVATE_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 567d13405445..77d16b90045c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12154,7 +12154,7 @@ 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 c262ebb168a7..1b203c8aa696 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/memfile_notifier.h>

#ifndef KVM_MAX_VCPU_IDS
#define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
@@ -576,8 +577,16 @@ struct kvm_memory_slot {
u32 flags;
short id;
u16 as_id;
+ struct file *private_file;
+ loff_t private_offset;
+ struct memfile_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;
@@ -1109,9 +1118,9 @@ 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 a36e78710382..c467c69b7ad7 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 private_offset;
+ __u32 private_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 private_offset;
+ __u32 private_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 a8c5c9f06b3c..ccaff13cc5b8 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -72,3 +72,6 @@ config KVM_XFER_TO_GUEST_WORK

config HAVE_KVM_PM_NOTIFIER
bool
+
+config HAVE_KVM_PRIVATE_MEM
+ bool
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3ae4944b9f15..230c8ff9659c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1508,7 +1508,7 @@ 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;

@@ -1902,7 +1902,7 @@ 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;
@@ -2006,7 +2006,7 @@ 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;

@@ -2018,7 +2018,7 @@ 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;
@@ -4608,6 +4608,33 @@ 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(private_offset);
+ SANITY_CHECK_MEM_REGION_EXT_FIELD(private_fd);
+}
+
static long kvm_vm_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg)
{
@@ -4631,14 +4658,35 @@ 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;
+ u32 flags;
+
+ kvm_sanity_check_user_mem_region_alias();
+
+ memset(&mem, 0, sizeof(mem));

r = -EFAULT;
- if (copy_from_user(&kvm_userspace_mem, argp,
- sizeof(kvm_userspace_mem)))
+
+ if (get_user(flags,
+ (u32 __user *)(argp + offsetof(typeof(mem), flags))))
+ goto out;
+
+ if (flags & KVM_MEM_PRIVATE) {
+ r = -EINVAL;
+ goto out;
+ }
+
+ size = sizeof(struct kvm_userspace_memory_region);
+
+ if (copy_from_user(&mem, argp, size))
+ goto out;
+
+ r = -EINVAL;
+ if ((flags ^ 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