[PATCH v4 00/12] KVM/hostmem: Support init-shared guest-memfd as VM backends

[PATCH v4 00/12] KVM/hostmem: Support init-shared guest-memfd as VM backends

[Michael Roth]

v1: https://lore.kernel.org/r/20251023185913.2923322-1-peterx@redhat.com
v2: https://lore.kernel.org/r/20251119172913.577392-1-peterx@redhat.com
v3: https://lore.kernel.org/r/20251215205203.1185099-1-peterx@redhat.com/
v4:
- Picked up v3 series from Peter Xu and rebased on 11.1.0
- Collected pending Reviewed-by's
- Per-patch changes:
  [01/12] Fix blank space (Xiaoyao)
          Fix commit message typos
  [02/12] Drop duplicated error-handling for capability checks
  [05/12] Fix up commit message, disambigurate "in-place" terminology (Xiaoyao)
  [07/12] Fix up commit message, disambigurate "in-place" terminology (Xiaoyao)
  [08/12] Disallow 'seal' and 'hugetlb' options based on guest-memfd=on
          Fix minor typo in comment
  [11/12] Fix up typo in g_test_skip() reason
          Pending: Move kvm_guest_memfd_init_shared_supported() to
            migration-util.c (Fabiano)

This patchset is also available at:

  https://github.com/amdese/qemu/commits/gmem-shared-mem-v4

and is based on top of v11.1.0


OVERVIEW
========

(cover letter shamelessly adapted from Peter's prior postings)

Recent kernels allow guest_memfd to be initialized with an 'init-shared'
flag that will default to allocating normal/non-private memory that can be
used to back non-confidential VMs.

This allows QEMU to make use of these init-shared guest_memfd instances via
a common memory backend that's usable for either provide a common memory
backend.

On the QEMU side, before this series, guest_memfd was only used for private
guest memory (and thus only applied to confidential VMs), and the guest_memfd
FDs would be created implicitly whenever a confidential environment was
detected/specified.

With this series, users can now explicitly configure QEMU to use guest_memfd
for non-private memory; thus, it can be used for non-confidential
VMs. It also has implications for confidential VMs, since with this series an
init-shared guest_memfd instance can now be specified for the shared memory
while the internally-allocated guest_memfd continues to be used for private
memory. This same infrastructure will also be used as the base for enabling
in-place conversion for confidential VMs, where these separate shared/private
paths will be modified to act on the same underlying guest_memfd instance and
use a unified pool of shared/private memory.

IMPLEMENTATION
==============

In the current patchset, I reused the memory-backend-memfd object, rather
than creating a new type of object.  After all, guest-memfd (at least from
userspace POV) works similarly like a memfd, except that it was tailored
for VM's use case. While there is potential that new guest_memfd features
may eventually necessitate introducing a dedicated guest_memfd memory
backend object, for now the memory-backend-memfd object is a good fit for
the current feature set.

This will also make it easier when in-place conversion comes around, since
confidential VMs typically already use memory-backend-memfd for their shared
memory, so by also making using that approach to specify the guest_memfd
backend for in-place conversion the command-line syntax remains similar, and
even allow choosing between memfd vs. guest_memfd to be handled automatically
based on whether or not we're dealing with a Confidential VM with in-place
conversion enabled.

This approach so far also does not involve gmem bindings to KVM instances,
hence it is not prone to issues when the same chunk of RAM will be attached
to more than one KVM memslots.

Now, instead of using a normal memfd backend using:

  -object memory-backend-memfd,id=ID,size=SIZE,share=on

One can also boot a VM with guest-memfd:

  -object memory-backend-memfd,id=ID,size=SIZE,share=on,guest-memfd=on

The init-shared guest-memfd relies on a recent kernel (6.18+). When run it on
an older qemu, you'll see errors like:

  qemu-system-x86_64: KVM does not support guest_memfd

One thing to mention is live migration is by default supported, however
postcopy is still currently not supported.  The postcopy support will have
some kernel dependency work to be merged in Linux first.

Thanks,

Peter Xu (11):
  kvm: Detect guest-memfd flags supported
  kvm: Provide explicit error for kvm_create_guest_memfd()
  ramblock: Rename guest_memfd to guest_memfd_private
  memory: Rename RAM_GUEST_MEMFD to RAM_GUEST_MEMFD_PRIVATE
  memory: Rename memory_region_has_guest_memfd() to *_private()
  hostmem: Rename guest_memfd to guest_memfd_private
  hostmem: Support fully shared guest memfd to back a VM
  machine: Rename machine_require_guest_memfd() to *_private()
  memory: Rename memory_region_init_ram_guest_memfd() to *_private()
  tests/migration-test: Support guest-memfd init shared mem type
  tests/migration-test: Add a precopy test for guest-memfd

Xiaoyao Li (1):
  kvm: Decouple memory attribute check from kvm_guest_memfd_supported

 qapi/qom.json                         |  6 ++-
 include/hw/boards.h                   |  2 +-
 include/system/hostmem.h              |  2 +-
 include/system/kvm.h                  |  1 +
 include/system/memory.h               | 27 ++++++------
 include/system/ram_addr.h             |  2 +-
 include/system/ramblock.h             |  7 +++-
 tests/qtest/migration/framework.h     |  4 ++
 accel/kvm/kvm-all.c                   | 33 ++++++++++++---
 accel/stubs/kvm-stub.c                |  6 +++
 backends/hostmem-file.c               |  2 +-
 backends/hostmem-memfd.c              | 55 +++++++++++++++++++++---
 backends/hostmem-ram.c                |  2 +-
 backends/hostmem-shm.c                |  2 +-
 backends/hostmem.c                    |  2 +-
 backends/igvm.c                       |  4 +-
 hw/core/machine.c                     |  2 +-
 hw/i386/pc.c                          |  6 +--
 hw/i386/pc_sysfw.c                    |  8 ++--
 hw/i386/x86-common.c                  |  8 ++--
 system/memory.c                       | 17 ++++----
 system/physmem.c                      | 37 ++++++++++-------
 target/i386/kvm/kvm.c                 |  3 +-
 tests/qtest/migration/framework.c     | 60 +++++++++++++++++++++++++++
 tests/qtest/migration/precopy-tests.c | 12 ++++++
 25 files changed, 239 insertions(+), 71 deletions(-)

-- 
2.50.1

[PATCH v4 01/12] kvm: Decouple memory attribute check from kvm_guest_memfd_supported

[Michael Roth]

From: Xiaoyao Li <xiaoyao.li@intel.com>

With the mmap support of guest memfd, KVM allows userspace to create
guest memfd serving as normal non-private memory for X86 DEFAULT VM.
However, KVM doesn't support private memory attribute for X86 DEFAULT
VM.

Make kvm_guest_memfd_supported not rely on KVM_MEMORY_ATTRIBUTE_PRIVATE
and check KVM_MEMORY_ATTRIBUTE_PRIVATE separately when the machine
requires guest_memfd to serve as private memory.

This allows QEMU to create guest memfd with mmap to serve as the memory
backend for X86 DEFAULT VM.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c    | 8 ++++++--
 accel/stubs/kvm-stub.c | 5 +++++
 include/system/kvm.h   | 1 +
 system/physmem.c       | 8 ++++++++
 4 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 83cbd120a8..cdc7554082 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1627,6 +1627,11 @@ int kvm_set_memory_attributes_shared(hwaddr start, uint64_t size)
     return kvm_set_memory_attributes(start, size, 0);
 }
 
+bool kvm_private_memory_attribute_supported(void)
+{
+    return !!(kvm_supported_memory_attributes & KVM_MEMORY_ATTRIBUTE_PRIVATE);
+}
+
 /* Called with KVMMemoryListener.slots_lock held */
 static void kvm_set_phys_mem(KVMMemoryListener *kml,
                              MemoryRegionSection *section, bool add)
@@ -3058,8 +3063,7 @@ static int kvm_init(AccelState *as, MachineState *ms)
     kvm_supported_memory_attributes = kvm_vm_check_extension(s, KVM_CAP_MEMORY_ATTRIBUTES);
     kvm_guest_memfd_supported =
         kvm_vm_check_extension(s, KVM_CAP_GUEST_MEMFD) &&
-        kvm_vm_check_extension(s, KVM_CAP_USER_MEMORY2) &&
-        (kvm_supported_memory_attributes & KVM_MEMORY_ATTRIBUTE_PRIVATE);
+        kvm_vm_check_extension(s, KVM_CAP_USER_MEMORY2);
     kvm_pre_fault_memory_supported = kvm_vm_check_extension(s, KVM_CAP_PRE_FAULT_MEMORY);
 
     if (s->kernel_irqchip_split == ON_OFF_AUTO_AUTO) {
diff --git a/accel/stubs/kvm-stub.c b/accel/stubs/kvm-stub.c
index 32b4b07403..3d34e3b99d 100644
--- a/accel/stubs/kvm-stub.c
+++ b/accel/stubs/kvm-stub.c
@@ -143,3 +143,8 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
 {
     return -ENOSYS;
 }
+
+bool kvm_private_memory_attribute_supported(void)
+{
+    return false;
+}
diff --git a/include/system/kvm.h b/include/system/kvm.h
index 714b8c7b01..d29624034c 100644
--- a/include/system/kvm.h
+++ b/include/system/kvm.h
@@ -551,6 +551,7 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp);
 
 int kvm_set_memory_attributes_private(hwaddr start, uint64_t size);
 int kvm_set_memory_attributes_shared(hwaddr start, uint64_t size);
+bool kvm_private_memory_attribute_supported(void);
 
 int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private);
 
diff --git a/system/physmem.c b/system/physmem.c
index c21ea92915..406338f165 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2192,6 +2192,14 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
                        object_get_typename(OBJECT(current_machine->cgs)));
             goto out_free;
         }
+
+        if (!kvm_private_memory_attribute_supported()) {
+            error_setg(errp, "cannot set up private guest memory for %s: "
+                       "KVM does not support private memory attribute",
+                       object_get_typename(OBJECT(current_machine->cgs)));
+            goto out_free;
+        }
+
         assert(new_block->guest_memfd < 0);
 
         ret = ram_block_coordinated_discard_require(true);
-- 
2.43.0

[PATCH v4 02/12] kvm: Detect guest-memfd flags supported

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Detect supported guest-memfd flags by the current kernel, and reject
creations of guest-memfd using invalid flags.  When the cap isn't
available, then no flag is supported.

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index cdc7554082..120cab1e22 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -107,6 +107,7 @@ bool kvm_pre_fault_memory_supported;
 static bool kvm_immediate_exit;
 static uint64_t kvm_supported_memory_attributes;
 static bool kvm_guest_memfd_supported;
+static uint64_t kvm_guest_memfd_flags_supported;
 static hwaddr kvm_max_slot_size = ~0;
 
 static const KVMCapabilityInfo kvm_required_capabilities[] = {
@@ -3065,6 +3066,8 @@ static int kvm_init(AccelState *as, MachineState *ms)
         kvm_vm_check_extension(s, KVM_CAP_GUEST_MEMFD) &&
         kvm_vm_check_extension(s, KVM_CAP_USER_MEMORY2);
     kvm_pre_fault_memory_supported = kvm_vm_check_extension(s, KVM_CAP_PRE_FAULT_MEMORY);
+    kvm_guest_memfd_flags_supported =
+        kvm_vm_check_extension(s, KVM_CAP_GUEST_MEMFD_FLAGS);
 
     if (s->kernel_irqchip_split == ON_OFF_AUTO_AUTO) {
         s->kernel_irqchip_split = mc->default_kernel_irqchip_split ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
@@ -4760,6 +4763,13 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
         return -1;
     }
 
+    if (flags & ~kvm_guest_memfd_flags_supported) {
+        error_setg(errp, "Current KVM instance does not support "
+                   "guest-memfd flag: 0x%"PRIx64,
+                   flags & ~kvm_guest_memfd_flags_supported);
+        return -1;
+    }
+
     fd = kvm_vm_ioctl(kvm_state, KVM_CREATE_GUEST_MEMFD, &guest_memfd);
     if (fd < 0) {
         error_setg_errno(errp, errno, "Error creating KVM guest_memfd");
-- 
2.43.0

[PATCH v4 03/12] kvm: Provide explicit error for kvm_create_guest_memfd()

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

So that there will be a verbal string returned when kvm not enabled, or
kvm not compiled.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c    | 5 +++++
 accel/stubs/kvm-stub.c | 1 +
 2 files changed, 6 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 120cab1e22..bda2e25a66 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -4758,6 +4758,11 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
         .flags = flags,
     };
 
+    if (!kvm_enabled()) {
+        error_setg(errp, "guest-memfd requires KVM accelerator");
+        return -1;
+    }
+
     if (!kvm_guest_memfd_supported) {
         error_setg(errp, "KVM does not support guest_memfd");
         return -1;
diff --git a/accel/stubs/kvm-stub.c b/accel/stubs/kvm-stub.c
index 3d34e3b99d..acbd0785e0 100644
--- a/accel/stubs/kvm-stub.c
+++ b/accel/stubs/kvm-stub.c
@@ -141,6 +141,7 @@ bool kvm_hwpoisoned_mem(void)
 
 int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
 {
+    error_setg(errp, "KVM is not enabled");
     return -ENOSYS;
 }
 
-- 
2.43.0

[PATCH v4 04/12] ramblock: Rename guest_memfd to guest_memfd_private

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Rename the field to reflect the fact that the guest_memfd in this case only
backs private portion of the ramblock rather than all of it.

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c       |  2 +-
 include/system/memory.h   |  7 ++++---
 include/system/ramblock.h |  7 ++++++-
 system/memory.c           |  2 +-
 system/physmem.c          | 33 +++++++++++++++++----------------
 5 files changed, 29 insertions(+), 22 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index bda2e25a66..3afe491242 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1729,7 +1729,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
         mem->ram_start_offset = ram_start_offset;
         mem->ram = ram;
         mem->flags = kvm_mem_flags(mr);
-        mem->guest_memfd = mr->ram_block->guest_memfd;
+        mem->guest_memfd = mr->ram_block->guest_memfd_private;
         mem->guest_memfd_offset = mem->guest_memfd >= 0 ?
                                   (uint8_t*)ram - mr->ram_block->host : 0;
 
diff --git a/include/system/memory.h b/include/system/memory.h
index 2192fc9bdc..96b0a0a444 100644
--- a/include/system/memory.h
+++ b/include/system/memory.h
@@ -1507,10 +1507,11 @@ bool memory_region_skip_iommu_map(const MemoryRegion *mr);
 void memory_region_set_skip_iommu_map(MemoryRegion *mr, bool skip);
 
 /**
- * memory_region_has_guest_memfd: check whether a memory region has guest_memfd
- *     associated
+ * memory_region_has_guest_memfd: check whether a memory region has
+ *     guest_memfd_private associated
  *
- * Returns %true if a memory region's ram_block has valid guest_memfd assigned.
+ * Returns %true if a memory region's ram_block has valid guest_memfd_private
+ * assigned.
  *
  * @mr: the memory region being queried
  */
diff --git a/include/system/ramblock.h b/include/system/ramblock.h
index f0639287bf..8ed5e10710 100644
--- a/include/system/ramblock.h
+++ b/include/system/ramblock.h
@@ -40,7 +40,12 @@ struct RAMBlock {
     Error *cpr_blocker;
     int fd;
     uint64_t fd_offset;
-    int guest_memfd;
+    /*
+     * When RAM_GUEST_MEMFD_PRIVATE flag is set, this ramblock can have
+     * private pages backed by guest_memfd_private specified, while shared
+     * pages are backed by the ramblock on its own.
+     */
+    int guest_memfd_private;
     RamBlockAttributes *attributes;
     size_t page_size;
     /* dirty bitmap used during migration */
diff --git a/system/memory.c b/system/memory.c
index 5fc36708ec..4e6d54148e 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -1843,7 +1843,7 @@ void memory_region_set_skip_iommu_map(MemoryRegion *mr, bool skip)
 
 bool memory_region_has_guest_memfd(const MemoryRegion *mr)
 {
-    return mr->ram_block && mr->ram_block->guest_memfd >= 0;
+    return mr->ram_block && mr->ram_block->guest_memfd_private >= 0;
 }
 
 uint8_t memory_region_get_dirty_log_mask(const MemoryRegion *mr)
diff --git a/system/physmem.c b/system/physmem.c
index 406338f165..b979518bf6 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2200,7 +2200,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
             goto out_free;
         }
 
-        assert(new_block->guest_memfd < 0);
+        assert(new_block->guest_memfd_private < 0);
 
         ret = ram_block_coordinated_discard_require(true);
         if (ret < 0) {
@@ -2210,9 +2210,9 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
             goto out_free;
         }
 
-        new_block->guest_memfd = kvm_create_guest_memfd(new_block->max_length,
-                                                        0, errp);
-        if (new_block->guest_memfd < 0) {
+        new_block->guest_memfd_private =
+            kvm_create_guest_memfd(new_block->max_length, 0, errp);
+        if (new_block->guest_memfd_private < 0) {
             qemu_mutex_unlock_ramlist();
             goto out_free;
         }
@@ -2229,7 +2229,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
         new_block->attributes = ram_block_attributes_create(new_block);
         if (!new_block->attributes) {
             error_setg(errp, "Failed to create ram block attribute");
-            close(new_block->guest_memfd);
+            close(new_block->guest_memfd_private);
             ram_block_coordinated_discard_require(false);
             qemu_mutex_unlock_ramlist();
             goto out_free;
@@ -2365,7 +2365,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, ram_addr_t max_size,
     new_block->max_length = max_size;
     new_block->resized = resized;
     new_block->flags = ram_flags;
-    new_block->guest_memfd = -1;
+    new_block->guest_memfd_private = -1;
     new_block->host = file_ram_alloc(new_block, max_size, fd,
                                      file_size < offset + max_size,
                                      offset, errp);
@@ -2538,7 +2538,7 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
     new_block->used_length = size;
     new_block->max_length = max_size;
     new_block->fd = -1;
-    new_block->guest_memfd = -1;
+    new_block->guest_memfd_private = -1;
     new_block->page_size = qemu_real_host_page_size();
     new_block->host = host;
     new_block->flags = ram_flags;
@@ -2589,8 +2589,8 @@ static void reclaim_ramblock(RAMBlock *block)
         qemu_anon_ram_free(block->host, block->max_length);
     }
 
-    if (block->guest_memfd >= 0) {
-        close(block->guest_memfd);
+    if (block->guest_memfd_private >= 0) {
+        close(block->guest_memfd_private);
         ram_block_coordinated_discard_require(false);
     }
 
@@ -2838,12 +2838,12 @@ int ram_block_rebind(Error **errp)
 
     RAMBLOCK_FOREACH(block) {
         if (block->flags & RAM_GUEST_MEMFD) {
-            if (block->guest_memfd >= 0) {
-                close(block->guest_memfd);
+            if (block->guest_memfd_private >= 0) {
+                close(block->guest_memfd_private);
             }
-            block->guest_memfd = kvm_create_guest_memfd(block->max_length,
-                                                        0, errp);
-            if (block->guest_memfd < 0) {
+            block->guest_memfd_private = kvm_create_guest_memfd(
+                block->max_length, 0, errp);
+            if (block->guest_memfd_private < 0) {
                 qemu_mutex_unlock_ramlist();
                 return -1;
             }
@@ -4227,7 +4227,7 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t offset, size_t length)
         return ret;
     }
 
-    if (rb->guest_memfd >= 0) {
+    if (rb->guest_memfd_private >= 0) {
         ret = ram_block_discard_guest_memfd_range(rb, offset, length);
     }
 
@@ -4241,7 +4241,8 @@ int ram_block_discard_guest_memfd_range(RAMBlock *rb, uint64_t offset,
 
 #ifdef CONFIG_FALLOCATE_PUNCH_HOLE
     /* ignore fd_offset with guest_memfd */
-    ret = fallocate(rb->guest_memfd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+    ret = fallocate(rb->guest_memfd_private,
+                    FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                     offset, length);
 
     if (ret) {
-- 
2.43.0

[PATCH v4 05/12] memory: Rename RAM_GUEST_MEMFD to RAM_GUEST_MEMFD_PRIVATE

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

This name is too generic, and can conflict with support for using
guest-memfd for shared memory. Add a _PRIVATE suffix to show what it
really means: it is using guest_memfd specifically for private memory;
whether or not guest_memfd is being used for shared memory is something
to be configured/determined separately.

This also paves way for in-place guest-memfd, which means we can have a
ramblock that allocates pages completely from guest-memfd (private or
shared).

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 backends/hostmem-file.c   |  2 +-
 backends/hostmem-memfd.c  |  2 +-
 backends/hostmem-ram.c    |  2 +-
 backends/hostmem-shm.c    |  2 +-
 include/system/memory.h   |  8 ++++----
 include/system/ramblock.h |  2 +-
 system/memory.c           |  2 +-
 system/physmem.c          | 10 +++++-----
 8 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 8e3219c061..1f20cd8fd6 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -86,7 +86,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     ram_flags |= fb->readonly ? RAM_READONLY_FD : 0;
     ram_flags |= fb->rom == ON_OFF_AUTO_ON ? RAM_READONLY : 0;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0;
+    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
     ram_flags |= fb->is_pmem ? RAM_PMEM : 0;
     ram_flags |= RAM_NAMED_FILE;
     return memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name,
diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index 923239f9cf..3f3e485709 100644
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -60,7 +60,7 @@ have_fd:
     backend->aligned = true;
     ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0;
+    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
     return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name,
                                           backend->size, ram_flags, fd, 0, errp);
 }
diff --git a/backends/hostmem-ram.c b/backends/hostmem-ram.c
index 062b1abb11..96ad29112d 100644
--- a/backends/hostmem-ram.c
+++ b/backends/hostmem-ram.c
@@ -30,7 +30,7 @@ ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     name = host_memory_backend_get_name(backend);
     ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0;
+    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
     return memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend),
                                                   name, backend->size,
                                                   ram_flags, errp);
diff --git a/backends/hostmem-shm.c b/backends/hostmem-shm.c
index 806e2670e0..e86fb2e0aa 100644
--- a/backends/hostmem-shm.c
+++ b/backends/hostmem-shm.c
@@ -54,7 +54,7 @@ have_fd:
     /* Let's do the same as memory-backend-ram,share=on would do. */
     ram_flags = RAM_SHARED;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0;
+    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
 
     return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
                                               backend_name, backend->size,
diff --git a/include/system/memory.h b/include/system/memory.h
index 96b0a0a444..e960738af5 100644
--- a/include/system/memory.h
+++ b/include/system/memory.h
@@ -262,7 +262,7 @@ typedef struct IOMMUTLBEvent {
 #define RAM_READONLY_FD (1 << 11)
 
 /* RAM can be private that has kvm guest memfd backend */
-#define RAM_GUEST_MEMFD   (1 << 12)
+#define RAM_GUEST_MEMFD_PRIVATE   (1 << 12)
 
 /*
  * In RAMBlock creation functions, if MAP_SHARED is 0 in the flags parameter,
@@ -1119,7 +1119,7 @@ void memory_region_init_io(MemoryRegion *mr,
  *        must be unique within any device
  * @size: size of the region.
  * @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_NORESERVE,
- *             RAM_GUEST_MEMFD.
+ *             RAM_GUEST_MEMFD_PRIVATE.
  * @errp: pointer to Error*, to store an error if it happens.
  *
  * Note that this function does not do anything to cause the data in the
@@ -1181,7 +1181,7 @@ bool memory_region_init_resizeable_ram(MemoryRegion *mr,
  *         (getpagesize()) will be used.
  * @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_PMEM,
  *             RAM_NORESERVE, RAM_PROTECTED, RAM_NAMED_FILE, RAM_READONLY,
- *             RAM_READONLY_FD, RAM_GUEST_MEMFD
+ *             RAM_READONLY_FD, RAM_GUEST_MEMFD_PRIVATE
  * @path: the path in which to allocate the RAM.
  * @offset: offset within the file referenced by path
  * @errp: pointer to Error*, to store an error if it happens.
@@ -1212,7 +1212,7 @@ bool memory_region_init_ram_from_file(MemoryRegion *mr,
  * @size: size of the region.
  * @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_PMEM,
  *             RAM_NORESERVE, RAM_PROTECTED, RAM_NAMED_FILE, RAM_READONLY,
- *             RAM_READONLY_FD, RAM_GUEST_MEMFD
+ *             RAM_READONLY_FD, RAM_GUEST_MEMFD_PRIVATE
  * @fd: the fd to mmap.
  * @offset: offset within the file referenced by fd
  * @errp: pointer to Error*, to store an error if it happens.
diff --git a/include/system/ramblock.h b/include/system/ramblock.h
index 8ed5e10710..4550a19a3f 100644
--- a/include/system/ramblock.h
+++ b/include/system/ramblock.h
@@ -251,7 +251,7 @@ static inline unsigned long int ramblock_recv_bitmap_offset(void *host_addr,
  *  @resized: callback after calls to qemu_ram_resize
  *  @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_PMEM,
  *              RAM_NORESERVE, RAM_PROTECTED, RAM_NAMED_FILE, RAM_READONLY,
- *              RAM_READONLY_FD, RAM_GUEST_MEMFD
+ *              RAM_READONLY_FD, RAM_GUEST_MEMFD_PRIVATE
  *  @mem_path or @fd: specify the backing file or device
  *  @offset: Offset into target file
  *  @grow: extend file if necessary (but an empty file is always extended).
diff --git a/system/memory.c b/system/memory.c
index 4e6d54148e..84dcd9954e 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -3660,7 +3660,7 @@ bool memory_region_init_ram_guest_memfd(MemoryRegion *mr, Object *owner,
                                         Error **errp)
 {
     if (!memory_region_init_ram_flags_nomigrate(mr, owner, name, size,
-                                                RAM_GUEST_MEMFD, errp)) {
+                                                RAM_GUEST_MEMFD_PRIVATE, errp)) {
         return false;
     }
     memory_region_register_ram(mr, owner);
diff --git a/system/physmem.c b/system/physmem.c
index b979518bf6..3a7a1a8b16 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2184,7 +2184,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
         }
     }
 
-    if (new_block->flags & RAM_GUEST_MEMFD) {
+    if (new_block->flags & RAM_GUEST_MEMFD_PRIVATE) {
         int ret;
 
         if (!kvm_enabled()) {
@@ -2321,7 +2321,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, ram_addr_t max_size,
     /* Just support these ram flags by now. */
     assert((ram_flags & ~(RAM_SHARED | RAM_PMEM | RAM_NORESERVE |
                           RAM_PROTECTED | RAM_NAMED_FILE | RAM_READONLY |
-                          RAM_READONLY_FD | RAM_GUEST_MEMFD |
+                          RAM_READONLY_FD | RAM_GUEST_MEMFD_PRIVATE |
                           RAM_RESIZEABLE)) == 0);
     assert(max_size >= size);
 
@@ -2478,7 +2478,7 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
     ram_flags &= ~RAM_PRIVATE;
 
     assert((ram_flags & ~(RAM_SHARED | RAM_RESIZEABLE | RAM_PREALLOC |
-                          RAM_NORESERVE | RAM_GUEST_MEMFD)) == 0);
+                          RAM_NORESERVE | RAM_GUEST_MEMFD_PRIVATE)) == 0);
     assert(!host ^ (ram_flags & RAM_PREALLOC));
     assert(max_size >= size);
 
@@ -2561,7 +2561,7 @@ RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
 RAMBlock *qemu_ram_alloc(ram_addr_t size, uint32_t ram_flags,
                          MemoryRegion *mr, Error **errp)
 {
-    assert((ram_flags & ~(RAM_SHARED | RAM_NORESERVE | RAM_GUEST_MEMFD |
+    assert((ram_flags & ~(RAM_SHARED | RAM_NORESERVE | RAM_GUEST_MEMFD_PRIVATE |
                           RAM_PRIVATE)) == 0);
     return qemu_ram_alloc_internal(size, size, NULL, NULL, ram_flags, mr, errp);
 }
@@ -2837,7 +2837,7 @@ int ram_block_rebind(Error **errp)
     qemu_mutex_lock_ramlist();
 
     RAMBLOCK_FOREACH(block) {
-        if (block->flags & RAM_GUEST_MEMFD) {
+        if (block->flags & RAM_GUEST_MEMFD_PRIVATE) {
             if (block->guest_memfd_private >= 0) {
                 close(block->guest_memfd_private);
             }
-- 
2.43.0

[PATCH v4 06/12] memory: Rename memory_region_has_guest_memfd() to *_private()

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Rename the function with "_private" suffix, to show that it returns true
only if it has an internal guest-memfd to back private pages (rather than
fully shared guest-memfd).

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c     | 6 +++---
 include/system/memory.h | 4 ++--
 system/memory.c         | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 3afe491242..9e73c84f7c 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -792,7 +792,7 @@ static int kvm_mem_flags(MemoryRegion *mr)
     if (readonly && kvm_readonly_mem_allowed) {
         flags |= KVM_MEM_READONLY;
     }
-    if (memory_region_has_guest_memfd(mr)) {
+    if (memory_region_has_guest_memfd_private(mr)) {
         assert(kvm_guest_memfd_supported);
         flags |= KVM_MEM_GUEST_MEMFD;
     }
@@ -1741,7 +1741,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
             abort();
         }
 
-        if (memory_region_has_guest_memfd(mr)) {
+        if (memory_region_has_guest_memfd_private(mr)) {
             err = kvm_set_memory_attributes_private(start_addr, slot_size);
             if (err) {
                 error_report("%s: failed to set memory attribute private: %s",
@@ -3372,7 +3372,7 @@ int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
         return ret;
     }
 
-    if (!memory_region_has_guest_memfd(mr)) {
+    if (!memory_region_has_guest_memfd_private(mr)) {
         /*
          * Because vMMIO region must be shared, guest TD may convert vMMIO
          * region to shared explicitly.  Don't complain such case.  See
diff --git a/include/system/memory.h b/include/system/memory.h
index e960738af5..e3096699ba 100644
--- a/include/system/memory.h
+++ b/include/system/memory.h
@@ -1507,7 +1507,7 @@ bool memory_region_skip_iommu_map(const MemoryRegion *mr);
 void memory_region_set_skip_iommu_map(MemoryRegion *mr, bool skip);
 
 /**
- * memory_region_has_guest_memfd: check whether a memory region has
+ * memory_region_has_guest_memfd_private: check whether a memory region has
  *     guest_memfd_private associated
  *
  * Returns %true if a memory region's ram_block has valid guest_memfd_private
@@ -1515,7 +1515,7 @@ void memory_region_set_skip_iommu_map(MemoryRegion *mr, bool skip);
  *
  * @mr: the memory region being queried
  */
-bool memory_region_has_guest_memfd(const MemoryRegion *mr);
+bool memory_region_has_guest_memfd_private(const MemoryRegion *mr);
 
 /**
  * memory_region_get_iommu: check whether a memory region is an iommu
diff --git a/system/memory.c b/system/memory.c
index 84dcd9954e..db52cfe90e 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -1841,7 +1841,7 @@ void memory_region_set_skip_iommu_map(MemoryRegion *mr, bool skip)
     mr->ram_device_skip_iommu_map = skip;
 }
 
-bool memory_region_has_guest_memfd(const MemoryRegion *mr)
+bool memory_region_has_guest_memfd_private(const MemoryRegion *mr)
 {
     return mr->ram_block && mr->ram_block->guest_memfd_private >= 0;
 }
-- 
2.43.0

[PATCH v4 07/12] hostmem: Rename guest_memfd to guest_memfd_private

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Rename the HostMemoryBackend.guest_memfd field to reflect what it really
means: whether it needs guest_memfd to back its private guest memory.
This will help avoid conflicts when we introduce supported for using
guest_memfd for shared guest memory via hostmem.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 backends/hostmem-file.c  | 2 +-
 backends/hostmem-memfd.c | 2 +-
 backends/hostmem-ram.c   | 2 +-
 backends/hostmem-shm.c   | 2 +-
 backends/hostmem.c       | 2 +-
 include/system/hostmem.h | 2 +-
 6 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 1f20cd8fd6..0e4cfd6dc6 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -86,7 +86,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     ram_flags |= fb->readonly ? RAM_READONLY_FD : 0;
     ram_flags |= fb->rom == ON_OFF_AUTO_ON ? RAM_READONLY : 0;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
+    ram_flags |= backend->guest_memfd_private ? RAM_GUEST_MEMFD_PRIVATE : 0;
     ram_flags |= fb->is_pmem ? RAM_PMEM : 0;
     ram_flags |= RAM_NAMED_FILE;
     return memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name,
diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index 3f3e485709..ea93f034e4 100644
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -60,7 +60,7 @@ have_fd:
     backend->aligned = true;
     ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
+    ram_flags |= backend->guest_memfd_private ? RAM_GUEST_MEMFD_PRIVATE : 0;
     return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name,
                                           backend->size, ram_flags, fd, 0, errp);
 }
diff --git a/backends/hostmem-ram.c b/backends/hostmem-ram.c
index 96ad29112d..6a507fad77 100644
--- a/backends/hostmem-ram.c
+++ b/backends/hostmem-ram.c
@@ -30,7 +30,7 @@ ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     name = host_memory_backend_get_name(backend);
     ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
+    ram_flags |= backend->guest_memfd_private ? RAM_GUEST_MEMFD_PRIVATE : 0;
     return memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend),
                                                   name, backend->size,
                                                   ram_flags, errp);
diff --git a/backends/hostmem-shm.c b/backends/hostmem-shm.c
index e86fb2e0aa..4766db6aad 100644
--- a/backends/hostmem-shm.c
+++ b/backends/hostmem-shm.c
@@ -54,7 +54,7 @@ have_fd:
     /* Let's do the same as memory-backend-ram,share=on would do. */
     ram_flags = RAM_SHARED;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
-    ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD_PRIVATE : 0;
+    ram_flags |= backend->guest_memfd_private ? RAM_GUEST_MEMFD_PRIVATE : 0;
 
     return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
                                               backend_name, backend->size,
diff --git a/backends/hostmem.c b/backends/hostmem.c
index 5dd5fb155c..d54d9091c3 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -290,7 +290,7 @@ static void host_memory_backend_init(Object *obj)
     /* TODO: convert access to globals to compat properties */
     backend->merge = machine_mem_merge(machine);
     backend->dump = machine_dump_guest_core(machine);
-    backend->guest_memfd = machine_require_guest_memfd(machine);
+    backend->guest_memfd_private = machine_require_guest_memfd(machine);
     backend->reserve = true;
     backend->prealloc_threads = machine->smp.cpus;
 }
diff --git a/include/system/hostmem.h b/include/system/hostmem.h
index 88fa791ac7..dcbf81aeae 100644
--- a/include/system/hostmem.h
+++ b/include/system/hostmem.h
@@ -76,7 +76,7 @@ struct HostMemoryBackend {
     uint64_t size;
     bool merge, dump, use_canonical_path;
     bool prealloc, is_mapped, share, reserve;
-    bool guest_memfd, aligned;
+    bool guest_memfd_private, aligned;
     uint32_t prealloc_threads;
     ThreadContext *prealloc_context;
     DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
-- 
2.43.0

[PATCH v4 08/12] hostmem: Support fully shared guest memfd to back a VM

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Host backends supports guest-memfd now by detecting whether it's a
confidential VM.  There's no way to choose it yet from the memory level to
use it fully shared.  If we use guest-memfd, it so far always implies we
need two layers of memory backends, while the guest-memfd only provides the
private set of pages.

This patch introduces a way so that QEMU can consume guest memfd as the
only source of memory to back the object (aka, fully shared).

To use the fully shared guest-memfd, one can add a memfd object with:

  -object memory-backend-memfd,guest-memfd=on,share=on

Note that share=on is required with fully shared guest_memfd.

PS: there's a trivial touch-up on fd<0 check, because the stub to create
guest-memfd may return negative but not -1.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 backends/hostmem-memfd.c | 56 ++++++++++++++++++++++++++++++++++++----
 qapi/qom.json            |  6 ++++-
 2 files changed, 56 insertions(+), 6 deletions(-)

diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index ea93f034e4..fbe65b00be 100644
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -18,6 +18,8 @@
 #include "qapi/error.h"
 #include "qom/object.h"
 #include "migration/cpr.h"
+#include "system/kvm.h"
+#include <linux/kvm.h>
 
 OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendMemfd, MEMORY_BACKEND_MEMFD)
 
@@ -28,6 +30,13 @@ struct HostMemoryBackendMemfd {
     bool hugetlb;
     uint64_t hugetlbsize;
     bool seal;
+    /*
+     * NOTE: this differs from HostMemoryBackend's guest_memfd_private,
+     * which represents an internally private guest-memfd that only backs
+     * private pages.  Instead, this flag marks the memory backend will
+     * 100% use the guest-memfd pages in-place.
+     */
+    bool guest_memfd;
 };
 
 static bool
@@ -47,11 +56,29 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         goto have_fd;
     }
 
-    fd = qemu_memfd_create(TYPE_MEMORY_BACKEND_MEMFD, backend->size,
-                           m->hugetlb, m->hugetlbsize, m->seal ?
-                           F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL : 0,
-                           errp);
-    if (fd == -1) {
+    if (m->guest_memfd) {
+        if (!backend->share) {
+            error_setg(errp, "guest-memfd=on must be used with share=on");
+            return false;
+        } else if (m->seal) {
+            error_setg(errp, "guest-memfd=on must be used with seal=off");
+            return false;
+        } else if (m->hugetlb) {
+            error_setg(errp, "guest-memfd=on must be used with hugetlb=off");
+        }
+
+        fd = kvm_create_guest_memfd(backend->size,
+                                    GUEST_MEMFD_FLAG_MMAP |
+                                    GUEST_MEMFD_FLAG_INIT_SHARED,
+                                    errp);
+    } else {
+        fd = qemu_memfd_create(TYPE_MEMORY_BACKEND_MEMFD, backend->size,
+                               m->hugetlb, m->hugetlbsize, m->seal ?
+                               F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL : 0,
+                               errp);
+    }
+
+    if (fd < 0) {
         return false;
     }
     cpr_save_fd(name, 0, fd);
@@ -65,6 +92,18 @@ have_fd:
                                           backend->size, ram_flags, fd, 0, errp);
 }
 
+static bool
+memfd_backend_get_guest_memfd(Object *o, Error **errp)
+{
+    return MEMORY_BACKEND_MEMFD(o)->guest_memfd;
+}
+
+static void
+memfd_backend_set_guest_memfd(Object *o, bool value, Error **errp)
+{
+    MEMORY_BACKEND_MEMFD(o)->guest_memfd = value;
+}
+
 static bool
 memfd_backend_get_hugetlb(Object *o, Error **errp)
 {
@@ -152,6 +191,13 @@ memfd_backend_class_init(ObjectClass *oc, const void *data)
         object_class_property_set_description(oc, "hugetlbsize",
                                               "Huge pages size (ex: 2M, 1G)");
     }
+
+    object_class_property_add_bool(oc, "guest-memfd",
+                                   memfd_backend_get_guest_memfd,
+                                   memfd_backend_set_guest_memfd);
+    object_class_property_set_description(oc, "guest-memfd",
+                                          "Use guest memfd");
+
     object_class_property_add_bool(oc, "seal",
                                    memfd_backend_get_seal,
                                    memfd_backend_set_seal);
diff --git a/qapi/qom.json b/qapi/qom.json
index c55776af7d..ee981fc44c 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -771,13 +771,17 @@
 # @seal: if true, create a sealed-file, which will block further
 #     resizing of the memory (default: true)
 #
+# @guest-memfd: if true, use guest-memfd to back the memory region.
+#     (default: false, since: 11.2)
+#
 # Since: 2.12
 ##
 { 'struct': 'MemoryBackendMemfdProperties',
   'base': 'MemoryBackendProperties',
   'data': { '*hugetlb': 'bool',
             '*hugetlbsize': 'size',
-            '*seal': 'bool' },
+            '*seal': 'bool',
+            '*guest-memfd': 'bool' },
   'if': 'CONFIG_LINUX' }
 
 ##
-- 
2.43.0

[PATCH v4 09/12] machine: Rename machine_require_guest_memfd() to *_private()

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Differenciate it from fully shared guest-memfd use cases.

When at it, add proper brackets in kvm_handle_hc_map_gpa_range() otherwise
checkpatch may complain.

Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 backends/hostmem.c       | 2 +-
 hw/core/machine.c        | 2 +-
 hw/i386/pc.c             | 2 +-
 hw/i386/pc_sysfw.c       | 4 ++--
 hw/i386/x86-common.c     | 4 ++--
 include/hw/core/boards.h | 2 +-
 target/i386/kvm/kvm.c    | 3 ++-
 7 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/backends/hostmem.c b/backends/hostmem.c
index d54d9091c3..0cc5adcd38 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -290,7 +290,7 @@ static void host_memory_backend_init(Object *obj)
     /* TODO: convert access to globals to compat properties */
     backend->merge = machine_mem_merge(machine);
     backend->dump = machine_dump_guest_core(machine);
-    backend->guest_memfd_private = machine_require_guest_memfd(machine);
+    backend->guest_memfd_private = machine_require_guest_memfd_private(machine);
     backend->reserve = true;
     backend->prealloc_threads = machine->smp.cpus;
 }
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 73b4d82b4a..b78e9c2135 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -1330,7 +1330,7 @@ bool machine_mem_merge(MachineState *machine)
     return machine->mem_merge;
 }
 
-bool machine_require_guest_memfd(MachineState *machine)
+bool machine_require_guest_memfd_private(MachineState *machine)
 {
     return machine->cgs && machine->cgs->require_guest_memfd;
 }
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index f064aa2b3e..3ca8468c0f 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -870,7 +870,7 @@ void pc_memory_init(PCMachineState *pcms,
 
     if (!is_tdx_vm()) {
         option_rom_mr = g_malloc(sizeof(*option_rom_mr));
-        if (machine_require_guest_memfd(machine)) {
+        if (machine_require_guest_memfd_private(machine)) {
             memory_region_init_ram_guest_memfd(option_rom_mr, NULL, "pc.rom",
                                             PC_ROM_SIZE, &error_fatal);
         } else {
diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
index 1a41a5972b..4a7694c131 100644
--- a/hw/i386/pc_sysfw.c
+++ b/hw/i386/pc_sysfw.c
@@ -51,7 +51,7 @@ static void pc_isa_bios_init(PCMachineState *pcms, MemoryRegion *isa_bios,
 
     /* map the last 128KB of the BIOS in ISA space */
     isa_bios_size = MIN(flash_size, 128 * KiB);
-    if (machine_require_guest_memfd(MACHINE(pcms))) {
+    if (machine_require_guest_memfd_private(MACHINE(pcms))) {
         memory_region_init_ram_guest_memfd(isa_bios, NULL, "isa-bios",
                                            isa_bios_size, &error_fatal);
     } else {
@@ -70,7 +70,7 @@ static void pc_isa_bios_init(PCMachineState *pcms, MemoryRegion *isa_bios,
            ((uint8_t*)flash_ptr) + (flash_size - isa_bios_size),
            isa_bios_size);
 
-    if (!machine_require_guest_memfd(current_machine)) {
+    if (!machine_require_guest_memfd_private(current_machine)) {
         memory_region_set_readonly(isa_bios, true);
     }
 }
diff --git a/hw/i386/x86-common.c b/hw/i386/x86-common.c
index 8f9419e7d3..dd526c561c 100644
--- a/hw/i386/x86-common.c
+++ b/hw/i386/x86-common.c
@@ -1036,7 +1036,7 @@ static void load_bios_from_file(X86MachineState *x86ms, const char *bios_name,
     ssize_t ret;
 
     /* BIOS load */
-    if (machine_require_guest_memfd(MACHINE(x86ms))) {
+    if (machine_require_guest_memfd_private(MACHINE(x86ms))) {
         memory_region_init_ram_guest_memfd(&x86ms->bios, NULL, "pc.bios",
                                            bios_size, &error_fatal);
         if (is_tdx_vm()) {
@@ -1106,7 +1106,7 @@ void x86_bios_rom_init(X86MachineState *x86ms, const char *default_firmware,
     bios_size = get_bios_size(x86ms, bios_name, filename);
     load_bios_from_file(x86ms, bios_name, filename, bios_size, isapc_ram_fw);
 
-    if (!machine_require_guest_memfd(MACHINE(x86ms))) {
+    if (!machine_require_guest_memfd_private(MACHINE(x86ms))) {
         /* map the last 128KB of the BIOS in ISA space */
         x86_isa_bios_init(&x86ms->isa_bios, rom_memory, &x86ms->bios,
                           !isapc_ram_fw);
diff --git a/include/hw/core/boards.h b/include/hw/core/boards.h
index 29c68931d8..7c46db4dd9 100644
--- a/include/hw/core/boards.h
+++ b/include/hw/core/boards.h
@@ -43,7 +43,7 @@ bool machine_usb(MachineState *machine);
 int machine_phandle_start(MachineState *machine);
 bool machine_dump_guest_core(MachineState *machine);
 bool machine_mem_merge(MachineState *machine);
-bool machine_require_guest_memfd(MachineState *machine);
+bool machine_require_guest_memfd_private(MachineState *machine);
 HotpluggableCPUList *machine_query_hotpluggable_cpus(MachineState *machine);
 void machine_set_cpu_numa_node(MachineState *machine,
                                const CpuInstanceProperties *props,
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 4272b6770c..176d65d44f 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -6488,8 +6488,9 @@ static int kvm_handle_hc_map_gpa_range(X86CPU *cpu, struct kvm_run *run)
     uint64_t gpa, size, attributes;
     int ret;
 
-    if (!machine_require_guest_memfd(current_machine))
+    if (!machine_require_guest_memfd_private(current_machine)) {
         return -EINVAL;
+    }
 
     gpa = run->hypercall.args[0];
     size = run->hypercall.args[1] * TARGET_PAGE_SIZE;
-- 
2.43.0

[PATCH v4 10/12] memory: Rename memory_region_init_ram_guest_memfd() to *_private()

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Differenciate it from fully shared guest-memfd use cases.

Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 backends/igvm.c         |  4 ++--
 hw/i386/pc.c            |  4 ++--
 hw/i386/pc_sysfw.c      |  4 ++--
 hw/i386/x86-common.c    |  4 ++--
 include/system/memory.h | 10 +++++-----
 system/memory.c         |  8 +++++---
 6 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/backends/igvm.c b/backends/igvm.c
index 80e87fe602..87e6290f46 100644
--- a/backends/igvm.c
+++ b/backends/igvm.c
@@ -256,8 +256,8 @@ static void *qigvm_prepare_memory(QIgvm *ctx, uint64_t addr, uint64_t size,
         igvm_pages = g_new0(MemoryRegion, 1);
         if (ctx->machine_state->cgs &&
             ctx->machine_state->cgs->require_guest_memfd) {
-            if (!memory_region_init_ram_guest_memfd(igvm_pages, NULL,
-                                                    region_name, size, errp)) {
+            if (!memory_region_init_ram_guest_memfd_private(
+                    igvm_pages, NULL, region_name, size, errp)) {
                 g_free(igvm_pages);
                 return NULL;
             }
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 3ca8468c0f..b9537edb82 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -871,8 +871,8 @@ void pc_memory_init(PCMachineState *pcms,
     if (!is_tdx_vm()) {
         option_rom_mr = g_malloc(sizeof(*option_rom_mr));
         if (machine_require_guest_memfd_private(machine)) {
-            memory_region_init_ram_guest_memfd(option_rom_mr, NULL, "pc.rom",
-                                            PC_ROM_SIZE, &error_fatal);
+            memory_region_init_ram_guest_memfd_private(
+                option_rom_mr, NULL, "pc.rom", PC_ROM_SIZE, &error_fatal);
         } else {
             memory_region_init_ram(option_rom_mr, NULL, "pc.rom", PC_ROM_SIZE,
                                 &error_fatal);
diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
index 4a7694c131..3e0b9e1d28 100644
--- a/hw/i386/pc_sysfw.c
+++ b/hw/i386/pc_sysfw.c
@@ -52,8 +52,8 @@ static void pc_isa_bios_init(PCMachineState *pcms, MemoryRegion *isa_bios,
     /* map the last 128KB of the BIOS in ISA space */
     isa_bios_size = MIN(flash_size, 128 * KiB);
     if (machine_require_guest_memfd_private(MACHINE(pcms))) {
-        memory_region_init_ram_guest_memfd(isa_bios, NULL, "isa-bios",
-                                           isa_bios_size, &error_fatal);
+        memory_region_init_ram_guest_memfd_private(
+            isa_bios, NULL, "isa-bios", isa_bios_size, &error_fatal);
     } else {
         memory_region_init_ram(isa_bios, NULL, "isa-bios", isa_bios_size,
                                &error_fatal);
diff --git a/hw/i386/x86-common.c b/hw/i386/x86-common.c
index dd526c561c..ffe9cc90b6 100644
--- a/hw/i386/x86-common.c
+++ b/hw/i386/x86-common.c
@@ -1037,8 +1037,8 @@ static void load_bios_from_file(X86MachineState *x86ms, const char *bios_name,
 
     /* BIOS load */
     if (machine_require_guest_memfd_private(MACHINE(x86ms))) {
-        memory_region_init_ram_guest_memfd(&x86ms->bios, NULL, "pc.bios",
-                                           bios_size, &error_fatal);
+        memory_region_init_ram_guest_memfd_private(
+            &x86ms->bios, NULL, "pc.bios", bios_size, &error_fatal);
         if (is_tdx_vm()) {
             tdx_set_tdvf_region(&x86ms->bios);
         }
diff --git a/include/system/memory.h b/include/system/memory.h
index e3096699ba..d9ccb0142b 100644
--- a/include/system/memory.h
+++ b/include/system/memory.h
@@ -1358,11 +1358,11 @@ bool memory_region_init_ram(MemoryRegion *mr,
                             uint64_t size,
                             Error **errp);
 
-bool memory_region_init_ram_guest_memfd(MemoryRegion *mr,
-                                        Object *owner,
-                                        const char *name,
-                                        uint64_t size,
-                                        Error **errp);
+bool memory_region_init_ram_guest_memfd_private(MemoryRegion *mr,
+                                                Object *owner,
+                                                const char *name,
+                                                uint64_t size,
+                                                Error **errp);
 
 /**
  * memory_region_init_rom: Initialize a ROM memory region.
diff --git a/system/memory.c b/system/memory.c
index db52cfe90e..05b2943bcd 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -3655,9 +3655,11 @@ bool memory_region_init_ram(MemoryRegion *mr, Object *owner,
     return true;
 }
 
-bool memory_region_init_ram_guest_memfd(MemoryRegion *mr, Object *owner,
-                                        const char *name, uint64_t size,
-                                        Error **errp)
+bool memory_region_init_ram_guest_memfd_private(MemoryRegion *mr,
+                                                Object *owner,
+                                                const char *name,
+                                                uint64_t size,
+                                                Error **errp)
 {
     if (!memory_region_init_ram_flags_nomigrate(mr, owner, name, size,
                                                 RAM_GUEST_MEMFD_PRIVATE, errp)) {
-- 
2.43.0

[PATCH v4 11/12] tests/migration-test: Support guest-memfd init shared mem type

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Support the guest-memfd type when the fd has init share enabled.  It means
the gmemfd can be used similarly to memfd.

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 tests/qtest/migration/framework.c | 60 +++++++++++++++++++++++++++++++
 tests/qtest/migration/framework.h |  4 +++
 2 files changed, 64 insertions(+)

diff --git a/tests/qtest/migration/framework.c b/tests/qtest/migration/framework.c
index a830b96f41..b7aef6b21c 100644
--- a/tests/qtest/migration/framework.c
+++ b/tests/qtest/migration/framework.c
@@ -26,6 +26,10 @@
 #include "qemu/range.h"
 #include "qemu/sockets.h"
 
+#ifdef CONFIG_LINUX
+#include <linux/kvm.h>
+#include <sys/ioctl.h>
+#endif
 
 #define QEMU_VM_FILE_MAGIC 0x5145564d
 #define QEMU_ENV_SRC "QTEST_QEMU_BINARY_SRC"
@@ -296,6 +300,9 @@ static char *migrate_mem_type_get_opts(MemType type, const char *memory_size)
     case MEM_TYPE_MEMFD:
         backend = g_strdup("-object memory-backend-memfd");
         break;
+    case MEM_TYPE_GUEST_MEMFD:
+        backend = g_strdup("-object memory-backend-memfd,guest-memfd=on");
+        break;
     default:
         g_assert_not_reached();
         break;
@@ -444,8 +451,55 @@ int migrate_args(char **from, char **to, MigrateStart *args)
     return 0;
 }
 
+static bool kvm_guest_memfd_init_shared_supported(const char **reason)
+{
+    assert(*reason == NULL);
+
+#ifdef CONFIG_LINUX
+    int ret, fd = -1;
+
+    if (!migration_get_env()->has_kvm) {
+        *reason = "KVM is not enabled in the current QEMU build";
+        goto out;
+    }
+
+    fd = open("/dev/kvm", O_RDWR);
+    if (fd < 0) {
+        *reason = "KVM module isn't available or missing permission";
+        goto out;
+    }
+
+    ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_GUEST_MEMFD);
+    if (!ret) {
+        *reason = "KVM module doesn't support guest-memfd";
+        goto out;
+    }
+
+    ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_GUEST_MEMFD_FLAGS);
+    if (ret < 0) {
+        *reason = "KVM doesn't support KVM_CAP_GUEST_MEMFD_FLAGS";
+        goto out;
+    }
+
+    if (!(ret & GUEST_MEMFD_FLAG_INIT_SHARED)) {
+        *reason = "KVM doesn't support GUEST_MEMFD_FLAG_INIT_SHARED";
+        goto out;
+    }
+out:
+    if (fd >= 0) {
+        close(fd);
+    }
+#else
+    *reason = "KVM not supported on non-Linux OS";
+#endif
+
+    return !*reason;
+}
+
 static bool migrate_mem_type_prepare(MemType type)
 {
+    const char *reason = NULL;
+
     switch (type) {
     case MEM_TYPE_SHMEM:
         if (!g_file_test("/dev/shm", G_FILE_TEST_IS_DIR)) {
@@ -453,6 +507,12 @@ static bool migrate_mem_type_prepare(MemType type)
             return false;
         }
         break;
+    case MEM_TYPE_GUEST_MEMFD:
+        if (!kvm_guest_memfd_init_shared_supported(&reason)) {
+            g_test_skip(reason);
+            return false;
+        }
+        break;
     default:
         break;
     }
diff --git a/tests/qtest/migration/framework.h b/tests/qtest/migration/framework.h
index 941cbd7102..10761f6e28 100644
--- a/tests/qtest/migration/framework.h
+++ b/tests/qtest/migration/framework.h
@@ -34,6 +34,10 @@ typedef enum {
      * but only anonymously allocated.
      */
     MEM_TYPE_MEMFD,
+    /*
+     * Use guest-memfd, shared mappings.
+     */
+    MEM_TYPE_GUEST_MEMFD,
     MEM_TYPE_NUM,
 } MemType;
 
-- 
2.43.0

[PATCH v4 12/12] tests/migration-test: Add a precopy test for guest-memfd

[Michael Roth]

From: Peter Xu <peterx@redhat.com>

Add a plain tcp test for guest-memfd.  Note that the test will be
automatically skipped whenever not supported (e.g. qemu compiled without
KVM, or host kernel doesn't support kvm, or old kernels, etc.).

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 tests/qtest/migration/precopy-tests.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tests/qtest/migration/precopy-tests.c b/tests/qtest/migration/precopy-tests.c
index a23d51126b..8146f37d61 100644
--- a/tests/qtest/migration/precopy-tests.c
+++ b/tests/qtest/migration/precopy-tests.c
@@ -182,6 +182,14 @@ static void test_precopy_tcp_plain(char *name, MigrateCommon *args)
     test_precopy_common(args);
 }
 
+static void test_precopy_tcp_plain_gmemfd(char *name, MigrateCommon *args)
+{
+    args->uri = "tcp:127.0.0.1:0";
+    args->start.mem_type = MEM_TYPE_GUEST_MEMFD;
+
+    test_precopy_common(args);
+}
+
 static void test_precopy_tcp_switchover_ack(char *name, MigrateCommon *args)
 {
     /*
@@ -1108,6 +1116,8 @@ void migration_test_add_precopy(MigrationTestEnv *env)
         return;
     }
 
+    migration_test_add("/migration/precopy/tcp/plain/guest-memfd",
+                       test_precopy_tcp_plain_gmemfd);
     migration_test_add("/migration/precopy/tcp/plain/switchover-ack",
                        test_precopy_tcp_switchover_ack);
 
-- 
2.43.0