(resending to fix Message-ID) Here's a second revision of guest_memfd In-place conversion support.
In this version, other than addressing comments from RFCv1 [1], the largest change is that guest_memfd now does not avoid participation in LRU; it participates in LRU by joining the unevictable list (no change from before this series). While checking for elevated refcounts during shared to private conversions, guest_memfd will now do an lru_add_drain_all() if elevated refcounts were found, before concluding that there are true users of the shared folio and erroring out. I'd still like feedback on these points, if any: 1. Having private/shared status stored in a maple tree (Thanks Michael for your support of using maple trees over xarrays for performance! [5]). 2. Having a new guest_memfd ioctl (not a vm ioctl) that performs conversions. 3. Using ioctls/structs/input attribute similar to the existing vm ioctl KVM_SET_MEMORY_ATTRIBUTES to perform conversions. 4. Storing requested attributes directly in the maple tree. 5. Using a KVM module-wide param to toggle between setting memory attributes via vm and guest_memfd ioctls (making them mututally exclusive - a single loaded KVM module can only do one of the two.). This series is based on kvm/next as at 2026-01-21, and here's the tree for your convenience: https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-v2 The "Don't set FGP_ACCESSED when getting folios" patch from RFCv1 is still useful but no longer related to conversion, and was posted separately [6]. Older series: + RFCv1 is at [1] + Previous versions of this feature, part of other series, are available at [2][3][4]. [1] https://lore.kernel.org/all/[email protected]/T/ [2] https://lore.kernel.org/all/bd163de3118b626d1005aa88e71ef2fb72f0be0f.1726009989.git.ackerley...@google.com/ [3] https://lore.kernel.org/all/[email protected]/ [4] https://lore.kernel.org/all/b784326e9ccae6a08388f1bf39db70a2204bdc51.1747264138.git.ackerley...@google.com/ [5] https://lore.kernel.org/all/[email protected]/ [6] https://lore.kernel.org/all/[email protected]/ Ackerley Tng (19): KVM: guest_memfd: Update kvm_gmem_populate() to use gmem attributes KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2 KVM: guest_memfd: Add support for KVM_SET_MEMORY_ATTRIBUTES2 KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check KVM: selftests: Update framework to use KVM_SET_MEMORY_ATTRIBUTES2 KVM: selftests: Test using guest_memfd for guest private memory KVM: selftests: Test basic single-page conversion flow KVM: selftests: Test conversion flow when INIT_SHARED KVM: selftests: Test indexing in guest_memfd KVM: selftests: Test conversion before allocation KVM: selftests: Convert with allocated folios in different layouts KVM: selftests: Test precision of conversion KVM: selftests: Test that truncation does not change shared/private status 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 KVM: selftests: Add script to exercise private_mem_conversions_test Sean Christopherson (18): 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: Stub in ability to disable per-VM memory attribute tracking KVM: guest_memfd: Wire up kvm_get_memory_attributes() to per-gmem attributes KVM: guest_memfd: Enable INIT_SHARED on guest_memfd for x86 Coco VMs KVM: Move KVM_VM_MEMORY_ATTRIBUTES config definition to x86 KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes 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: Check fd/flags provided to mmap() when setting up memslot KVM: selftests: Update pre-fault test to work with per-guest_memfd attributes KVM: selftests: Update private memory exits test work with per-gmem attributes Documentation/virt/kvm/api.rst | 72 ++- arch/x86/include/asm/kvm_host.h | 2 +- arch/x86/kvm/Kconfig | 15 +- arch/x86/kvm/mmu/mmu.c | 4 +- arch/x86/kvm/x86.c | 13 +- include/linux/kvm_host.h | 53 +- include/trace/events/kvm.h | 4 +- include/uapi/linux/kvm.h | 17 + tools/testing/selftests/kvm/.gitignore | 1 + tools/testing/selftests/kvm/Makefile.kvm | 1 + .../kvm/guest_memfd_conversions_test.c | 486 ++++++++++++++++++ .../testing/selftests/kvm/guest_memfd_test.c | 57 +- .../testing/selftests/kvm/include/kvm_util.h | 128 ++++- .../testing/selftests/kvm/include/test_util.h | 31 +- tools/testing/selftests/kvm/lib/kvm_util.c | 130 +++-- tools/testing/selftests/kvm/lib/test_util.c | 7 - .../selftests/kvm/pre_fault_memory_test.c | 2 +- .../kvm/x86/private_mem_conversions_test.c | 48 +- .../kvm/x86/private_mem_conversions_test.py | 152 ++++++ .../kvm/x86/private_mem_kvm_exits_test.c | 36 +- virt/kvm/Kconfig | 4 +- virt/kvm/guest_memfd.c | 399 +++++++++++++- virt/kvm/kvm_main.c | 104 +++- 23 files changed, 1590 insertions(+), 176 deletions(-) create mode 100644 tools/testing/selftests/kvm/guest_memfd_conversions_test.c create mode 100755 tools/testing/selftests/kvm/x86/private_mem_conversions_test.py -- 2.53.0.rc1.225.gd81095ad13-goog
