[PATCH v9 00/41] guest_memfd: In-place conversion support
From: Ackerley Tng via B4 Relay
Date: Tue Jul 28 2026 - 20:43:13 EST
This is v9 of guest_memfd in-place conversion support. Please find the
motivation for this series from v8 and before.
Here are the changes from v8->v9:
+ Ordering changes: Reverted to the v7 and
github/sean-jc/linux/x86/gmem_inplace ordering.
+ Xiaoyao/Sean, hope this works better.
+ For Sean (since github/sean-jc/linux/x86/gmem_inplace was never on-list)
+ Extracted these patches out of your "KVM: guest_memfd: Wire up
core per-gmem attribute interfaces" to have the wiring up patch
focus on wiring up.
+ "KVM: guest_memfd: Introduce function to check GFN
private/shared status"
+ "guest_memfd: Introduce function to check GFN private/shared
status"
+ Moved the patches that allow conversions for TDX and SNP after
the TDX and SNP changes to make source addr optional, so that
once conversions can be used with TDX they will work.
+ Added to the description of "KVM: Let userspace disable per-VM
mem attributes, enable per-gmem attributes" to explain the
components of the change better.
+ Centralized interpretation of a maple tree entry - the part where
guest_memfd will default to the initial shared/private state if
entry is NULL - into kvm_gmem_interpret_entry().
+ "KVM: selftests: Add support for mmap() on guest_memfd in core library"
+ For guest_memfd, always mmap with MAP_SHARED. guest_memfd only
supports MAP_SHARED.
+ Dropped "KVM: selftests: Check fd/flags provided to mmap() when
setting up memslot" [1], since it was meant to check that when a
guest_memfd is used as region->fd, the flag provided to mmap()
will include MAP_SHARED.
+ "KVM: guest_memfd: Wire up core private/shared attribute interfaces"
+ Renamed kvm_gmem_range_is_private() to kvm_range_is_private()
since this function checks both VM and guest_memfd attributes.
+ Dropped "Use actual size for invalidation in kvm_gmem_release()"
since now the invalidation logic doesn't determine filter based on
range. Only zap pages not already in the desired state. [Suzuki]
+ To address Vlastimil and David's comments [2] on freezing refcounts,
in this patch series we're checking for safe refcounts to ensure
that there are no other users of the memory. For this series, we can
tolerate speculative bump+release of the refcounts, since those
don't access memory. I'll definitely re-look refcount freezing when
we get to the point that we need to restructure (split/merge) huge
pages. Thanks!
+ Addressed the other comments from v8
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
This series is based on kvm-x86/next, and here's the tree for your convenience:
https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-v9
I tested v9 with CoCo selftests on top of the branch above:
https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-coco-selftests-v9
Older series:
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/
[1] https://lore.kernel.org/all/20260618-gmem-inplace-conversion-v8-43-9d2959357853@xxxxxxxxxx/
[2] https://lore.kernel.org/all/088e9969-9104-4163-8ad4-59bec96014e0@xxxxxxxxxx/
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
Ackerley Tng (23):
KVM: guest_memfd: Introduce function to check GFN private/shared status
KVM: guest_memfd: Filter both shared and private when invalidating
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
mm: swap: Introduce lru_add_drain_progressive()
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: Let userspace disable per-VM mem attributes, enable per-gmem attributes
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: Update private_mem_conversions_test to mmap() guest_memfd
Michael Roth (1):
KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE
Sean Christopherson (17):
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: Wire up core private/shared attribute interfaces
KVM: Consolidate private memory and guest_memfd ifdeffery in kvm_host.h
KVM: Move KVM_VM_MEMORY_ATTRIBUTES config definition to x86
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/virt/kvm/api.rst | 78 +++-
.../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 | 6 +-
arch/x86/kvm/Kconfig | 15 +-
arch/x86/kvm/mmu/mmu.c | 16 +-
arch/x86/kvm/svm/sev.c | 11 +-
arch/x86/kvm/vmx/tdx.c | 8 +-
arch/x86/kvm/x86.c | 20 +-
include/linux/kvm_host.h | 76 +--
include/linux/swap.h | 2 +
include/trace/events/kvm.h | 6 +-
include/uapi/linux/kvm.h | 16 +
mm/gup.c | 19 +-
mm/swap.c | 17 +
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 | 164 ++++---
tools/testing/selftests/kvm/lib/test_util.c | 7 -
.../kvm/x86/guest_memfd_conversions_test.c | 509 +++++++++++++++++++++
.../kvm/x86/private_mem_conversions_test.c | 53 ++-
.../selftests/kvm/x86/private_mem_kvm_exits_test.c | 36 +-
virt/kvm/Kconfig | 3 -
virt/kvm/guest_memfd.c | 465 +++++++++++++++++--
virt/kvm/kvm_main.c | 92 ++--
27 files changed, 1551 insertions(+), 262 deletions(-)
---
base-commit: 3c7d7f908d574277a845423ec32250a8d8df44c8
change-id: 20260225-gmem-inplace-conversion-bd0dbd39753a
Best regards,
--
Ackerley Tng <ackerleytng@xxxxxxxxxx>