[PATCH v12 00/45] guest_memfd: In-place conversion support
From: Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>
Date: 2026-08-31 00:25:25
Also in:
b4-sent, kvm, linux-coco, linux-doc, linux-kselftest, linux-mm, lkml
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/ (local) [2] https://lore.kernel.org/all/apCj6gz8x24Dkle8@google.com/ (local) [3] https://lore.kernel.org/all/20260826-gmem-no-return-page-v4-0-3bb9c1ddb4e3@google.com/ (local) 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 (local) v9: https://lore.kernel.org/r/20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@google.com (local) v8: https://lore.kernel.org/r/20260618-gmem-inplace-conversion-v8-0-9d2959357853@google.com (local) v7: https://lore.kernel.org/r/20260522-gmem-inplace-conversion-v7-0-2f0fae496530@google.com (local) v6: https://lore.kernel.org/r/20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4@google.com (local) RFC v5: https://lore.kernel.org/r/20260428-gmem-inplace-conversion-v5-0-d8608ccfca22@google.com (local) RFC v4: https://lore.kernel.org/all/20260326-gmem-inplace-conversion-v4-0-e202fe950ffd@google.com/T/ (local) RFC v3: https://lore.kernel.org/r/20260313-gmem-inplace-conversion-v3-0-5fc12a70ec89@google.com/T/ (local) RFC v2: https://lore.kernel.org/all/cover.1770071243.git.ackerleytng@google.com/T/ (local) RFC v1: https://lore.kernel.org/all/cover.1760731772.git.ackerleytng@google.com/T/ (local) Previous versions of this feature, part of other series, are available at: + https://lore.kernel.org/all/bd163de3118b626d1005aa88e71ef2fb72f0be0f.1726009989.git.ackerleytng@google.com/ (local) + https://lore.kernel.org/all/20250117163001.2326672-6-tabba@google.com/ (local) + https://lore.kernel.org/all/b784326e9ccae6a08388f1bf39db70a2204bdc51.1747264138.git.ackerleytng@google.com/ (local) Signed-off-by: Ackerley Tng <redacted> --- 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 [off-list ref]