[PATCH v12 00/45] guest_memfd: In-place conversion support
From: Ackerley Tng via B4 Relay
Date: Sun Aug 30 2026 - 20:27:05 EST
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@xxxxxxxxxx/
[2] https://lore.kernel.org/all/apCj6gz8x24Dkle8@xxxxxxxxxx/
[3] https://lore.kernel.org/all/20260826-gmem-no-return-page-v4-0-3bb9c1ddb4e3@xxxxxxxxxx/
v11: https://patch.msgid.link/20260826-gmem-inplace-conversion-v11-0-0a15d8a799aa@xxxxxxxxxx
v10: https://lore.kernel.org/r/20260807-gmem-inplace-conversion-v10-0-2fc18ee6d3ba@xxxxxxxxxx
v9: https://lore.kernel.org/r/20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@xxxxxxxxxx
v8: https://lore.kernel.org/r/20260618-gmem-inplace-conversion-v8-0-9d2959357853@xxxxxxxxxx
v7: https://lore.kernel.org/r/20260522-gmem-inplace-conversion-v7-0-2f0fae496530@xxxxxxxxxx
v6: https://lore.kernel.org/r/20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4@xxxxxxxxxx
RFC v5: https://lore.kernel.org/r/20260428-gmem-inplace-conversion-v5-0-d8608ccfca22@xxxxxxxxxx
RFC v4: https://lore.kernel.org/all/20260326-gmem-inplace-conversion-v4-0-e202fe950ffd@xxxxxxxxxx/T/
RFC v3: https://lore.kernel.org/r/20260313-gmem-inplace-conversion-v3-0-5fc12a70ec89@xxxxxxxxxx/T/
RFC v2: https://lore.kernel.org/all/cover.1770071243.git.ackerleytng@xxxxxxxxxx/T/
RFC v1: https://lore.kernel.org/all/cover.1760731772.git.ackerleytng@xxxxxxxxxx/T/
Previous versions of this feature, part of other series, are available at:
+ https://lore.kernel.org/all/bd163de3118b626d1005aa88e71ef2fb72f0be0f.1726009989.git.ackerleytng@xxxxxxxxxx/
+ https://lore.kernel.org/all/20250117163001.2326672-6-tabba@xxxxxxxxxx/
+ https://lore.kernel.org/all/b784326e9ccae6a08388f1bf39db70a2204bdc51.1747264138.git.ackerleytng@xxxxxxxxxx/
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
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@xxxxxxxxxx>