[PATCH v12 00/45] guest_memfd: In-place conversion support

[Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>]

Here's v12. Thanks everyone for the comments and fast responses!  We're now
at ~4 weeks to soft-close at 7.3-rc5.

v12 is based on 7.3-rc1 (contains the mm/ bugfixes). Like v11, v12 is also
dependent on another series [3], which makes kvm_gmem_get_pfn() NOT return
a refcounted page to KVM.

Here's everything stitched together for your convenience:

https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-v12

This revision resolves the issue on v10/v11 to do with over-zapping of
non-gmem memory because of the requested filters. [1]

The resolution is in a new patch "KVM: guest_memfd: Always fault from
guest_memfd if in-place conversion is enabled". I also updated the
documentation as requested.

Documentation updates are in these patches:

+ KVM: guest_memfd: Stub in ability to enable in-place shared<=>private conversion
+ KVM: guest_memfd: Always fault from guest_memfd if in-place conversion is enabled
+ KVM: guest_memfd: Add base support for KVM_SET_MEMORY_ATTRIBUTES2

The documentation update in v10's "KVM: Let userspace disable per-VM mem
attributes, enable per-gmem attributes" was misplaced imo so I folded it
conceptually into the patches above.

private_mem_conversions_test was updated in v11 to test dual backing, and
that's meaningless now since with gmem_in_place_conversions, we're now
always faulting from guest_memfd, and the userspace_addr not being from the
gmem associated with the memslot is considered a user error.

I now only have 1 patch "KVM: selftests: Update
private_mem_conversions_test for in-place conversions" instead of 2 in v11.

Resolves discussion at [2].

Here's v12 with tests:

https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-coco-selftests-v12

Tested with both CONFIG_KVM_VM_MEMORY_ATTRIBUTES enabled and disabled:

+ tools/testing/selftests/kvm/guest_memfd_test.c
+ tools/testing/selftests/kvm/pre_fault_memory_test.c
+ tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c
+ tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
+ tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c

[1] https://lore.kernel.org/all/apCLFSbj8sq2biJp@google.com/
[2] https://lore.kernel.org/all/apCj6gz8x24Dkle8@google.com/
[3] https://lore.kernel.org/all/20260826-gmem-no-return-page-v4-0-3bb9c1ddb4e3@google.com/

v11: https://patch.msgid.link/20260826-gmem-inplace-conversion-v11-0-0a15d8a799aa@google.com
v10: https://lore.kernel.org/r/20260807-gmem-inplace-conversion-v10-0-2fc18ee6d3ba@google.com
v9: https://lore.kernel.org/r/20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@google.com
v8: https://lore.kernel.org/r/20260618-gmem-inplace-conversion-v8-0-9d2959357853@google.com
v7: https://lore.kernel.org/r/20260522-gmem-inplace-conversion-v7-0-2f0fae496530@google.com
v6: https://lore.kernel.org/r/20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4@google.com
RFC v5: https://lore.kernel.org/r/20260428-gmem-inplace-conversion-v5-0-d8608ccfca22@google.com
RFC v4: https://lore.kernel.org/all/20260326-gmem-inplace-conversion-v4-0-e202fe950ffd@google.com/T/
RFC v3: https://lore.kernel.org/r/20260313-gmem-inplace-conversion-v3-0-5fc12a70ec89@google.com/T/
RFC v2: https://lore.kernel.org/all/cover.1770071243.git.ackerleytng@google.com/T/
RFC v1: https://lore.kernel.org/all/cover.1760731772.git.ackerleytng@google.com/T/

Previous versions of this feature, part of other series, are available at:

+ https://lore.kernel.org/all/bd163de3118b626d1005aa88e71ef2fb72f0be0f.1726009989.git.ackerleytng@google.com/
+ https://lore.kernel.org/all/20250117163001.2326672-6-tabba@google.com/
+ https://lore.kernel.org/all/b784326e9ccae6a08388f1bf39db70a2204bdc51.1747264138.git.ackerleytng@google.com/

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
Ackerley Tng (23):
      KVM: Rename kvm_mem_is_private() to kvm_is_private_gfn()
      KVM: guest_memfd: Always fault from guest_memfd if in-place conversion is enabled
      KVM: guest_memfd: Pass mapping type filter to invalidation helper
      KVM: guest_memfd: Add base support for KVM_SET_MEMORY_ATTRIBUTES2
      KVM: guest_memfd: Ensure pages are not in use before conversion
      KVM: guest_memfd: Call arch make_shared callback for to-shared conversion
      KVM: guest_memfd: Return early if range already has requested attributes
      KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check
      KVM: guest_memfd: Zero page while getting pfn
      KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION
      KVM: selftests: Test basic single-page conversion flow
      KVM: selftests: Test conversion flow when INIT_SHARED
      KVM: selftests: Test conversion precision in guest_memfd
      KVM: selftests: Test conversion before allocation
      KVM: selftests: Convert with allocated folios in different layouts
      KVM: selftests: Test that truncation does not change shared/private status
      KVM: selftests: Add helpers to pin pages with CONFIG_GUP_TEST
      KVM: selftests: Test conversion with elevated page refcount
      KVM: selftests: Reset shared memory after hole-punching
      KVM: selftests: Provide function to look up guest_memfd details from gpa
      KVM: selftests: Make TEST_EXPECT_SIGBUS thread-safe
      KVM: selftests: Set up page size and alignment independently for guest_memfd
      KVM: selftests: Update private_mem_conversions_test for in-place conversions

Michael Roth (1):
      KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE

Sean Christopherson (21):
      KVM: guest_memfd: Optimize away conversion overheads via dead-code elimination
      KVM: guest_memfd: Use kvm_mem_is_private() when populating guest_memfd memory
      KVM: guest_memfd: Introduce per-gmem attributes, use to guard user mappings
      KVM: Rename KVM_GENERIC_MEMORY_ATTRIBUTES to KVM_VM_MEMORY_ATTRIBUTES
      KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem is defined
      KVM: Rename memory attribute APIs to prepare for in-place gmem conversion
      KVM: Provide generic interface for checking memory private/shared status
      KVM: guest_memfd: Stub in ability to enable in-place shared<=>private conversion
      KVM: Consolidate private memory and guest_memfd ifdeffery in kvm_host.h
      KVM: guest_memfd: Invalidate both SHARED and PRIVATE mappings for in-place conversions
      KVM: Move KVM_VM_MEMORY_ATTRIBUTES config definition to x86
      KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes
      KVM: guest_memfd: Enable INIT_SHARED on guest_memfd for x86 Coco VMs
      KVM: selftests: Create gmem fd before "regular" fd when adding memslot
      KVM: selftests: Rename guest_memfd{,_offset} to gmem_{fd,offset}
      KVM: selftests: Add support for mmap() on guest_memfd in core library
      KVM: selftests: Add selftests global for guest memory attributes capability
      KVM: selftests: Add helpers for calling ioctls on guest_memfd
      KVM: selftests: Test that shared/private status is consistent across processes
      KVM: selftests: Provide common function to set memory attributes
      KVM: selftests: Update private memory exits test to work with per-gmem attributes

 Documentation/admin-guide/kernel-parameters.txt    |  25 +
 Documentation/virt/kvm/api.rst                     | 107 ++++-
 .../virt/kvm/x86/amd-memory-encryption.rst         |  14 +-
 Documentation/virt/kvm/x86/intel-tdx.rst           |   4 +
 arch/x86/include/asm/kvm-x86-ops.h                 |   2 +-
 arch/x86/include/asm/kvm_host.h                    |   9 +-
 arch/x86/kvm/Kconfig                               |  15 +-
 arch/x86/kvm/mmu/mmu.c                             |  28 +-
 arch/x86/kvm/svm/sev.c                             |  13 +-
 arch/x86/kvm/vmx/tdx.c                             |   8 +-
 arch/x86/kvm/x86.c                                 |  20 +-
 include/linux/kvm_host.h                           |  83 ++--
 include/trace/events/kvm.h                         |   6 +-
 include/uapi/linux/kvm.h                           |  16 +
 mm/folio.c                                         |   2 +
 tools/testing/selftests/kvm/Makefile.kvm           |   1 +
 tools/testing/selftests/kvm/include/kvm_util.h     | 139 +++++-
 tools/testing/selftests/kvm/include/test_util.h    |  34 +-
 tools/testing/selftests/kvm/lib/kvm_util.c         | 222 +++++----
 tools/testing/selftests/kvm/lib/test_util.c        |   7 -
 .../kvm/x86/guest_memfd_conversions_test.c         | 512 +++++++++++++++++++++
 .../kvm/x86/private_mem_conversions_test.c         |  66 ++-
 .../selftests/kvm/x86/private_mem_kvm_exits_test.c |  36 +-
 virt/kvm/Kconfig                                   |   3 -
 virt/kvm/guest_memfd.c                             | 469 +++++++++++++++++--
 virt/kvm/kvm_main.c                                |  92 ++--
 26 files changed, 1646 insertions(+), 287 deletions(-)
---
base-commit: a0c789941a3d705d00c018b3c9348b4b930c0c74
change-id: 20260225-gmem-inplace-conversion-bd0dbd39753a

Best regards,
--
Ackerley Tng <ackerleytng@google.com>