[RFC PATCH v1 00/37] guest_memfd: In-place conversion support

[Ackerley Tng <ackerleytng@google.com>]

Hello,

IIUC this is the first independent patch series for guest_memfd's in-place
conversion series! Happy to finally bring this out on its own.

Previous versions of this feature, part of other series, are available at
[1][2][3].

Many prior discussions have led up to these main features of this series, and
these are the main points I'd like feedback on.

1. Having private/shared status stored in a maple tree (Thanks Michael for your
   support of using maple trees over xarrays for performance! [4]).
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.)
6. Skipping LRU in guest_memfd folios - make guest_memfd folios not participate
   in LRU to avoid LRU refcounts from interfering with conversions.

This series is based on kvm/next, followed by

+ v12 of NUMA mempolicy support patches [5]
+ 3 cleanup patches from Sean [6][7][8]

Everything is stitched together here for your convenience

https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-v1

Thank you all for helping with this series!

If I missed out your comment from a previous series, it's not intentional!
Please do raise it again.

TODOs:

+ There might be an issue with memory failure handling because when guest_memfd
  folios stop participating in LRU. From a preliminary analysis,
  HWPoisonHandlable() is only true if PageLRU() is true. This needs further
  investigation.

[1] https://lore.kernel.org/all/bd163de3118b626d1005aa88e71ef2fb72f0be0f.1726009989.git.ackerleytng@google.com/
[2] https://lore.kernel.org/all/20250117163001.2326672-6-tabba@google.com/
[3] https://lore.kernel.org/all/b784326e9ccae6a08388f1bf39db70a2204bdc51.1747264138.git.ackerleytng@google.com/
[4] https://lore.kernel.org/all/20250529054227.hh2f4jmyqf6igd3i@amd.com/
[5] https://lore.kernel.org/all/20251007221420.344669-1-seanjc@google.com/T/
[6] https://lore.kernel.org/all/20250924174255.2141847-1-seanjc@google.com/
[7] https://lore.kernel.org/all/20251007224515.374516-1-seanjc@google.com/
[8] https://lore.kernel.org/all/20251007223625.369939-1-seanjc@google.com/

Ackerley Tng (19):
  KVM: guest_memfd: Update kvm_gmem_populate() to use gmem attributes
  KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2
  KVM: guest_memfd: Don't set FGP_ACCESSED when getting folios
  KVM: guest_memfd: Skip LRU for guest_memfd folios
  KVM: guest_memfd: Add support for KVM_SET_MEMORY_ATTRIBUTES
  KVM: selftests: Update framework to use KVM_SET_MEMORY_ATTRIBUTES2
  KVM: selftests: guest_memfd: Test basic single-page conversion flow
  KVM: selftests: guest_memfd: Test conversion flow when INIT_SHARED
  KVM: selftests: guest_memfd: Test indexing in guest_memfd
  KVM: selftests: guest_memfd: Test conversion before allocation
  KVM: selftests: guest_memfd: Convert with allocated folios in
    different layouts
  KVM: selftests: guest_memfd: Test precision of conversion
  KVM: selftests: guest_memfd: Test that truncation does not change
    shared/private status
  KVM: selftests: guest_memfd: 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 helpers for calling ioctls on guest_memfd
  KVM: selftests: guest_memfd: Test that shared/private status is
    consistent across processes
  KVM: selftests: Add selftests global for guest memory attributes
    capability
  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                      |  44 +-
 include/trace/events/kvm.h                    |   4 +-
 include/uapi/linux/kvm.h                      |  17 +
 mm/filemap.c                                  |   1 +
 mm/memcontrol.c                               |   2 +
 tools/testing/selftests/kvm/.gitignore        |   1 +
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../kvm/guest_memfd_conversions_test.c        | 498 ++++++++++++++++++
 .../testing/selftests/kvm/include/kvm_util.h  | 127 ++++-
 .../testing/selftests/kvm/include/test_util.h |  29 +-
 tools/testing/selftests/kvm/lib/kvm_util.c    | 128 +++--
 tools/testing/selftests/kvm/lib/test_util.c   |   7 -
 .../selftests/kvm/pre_fault_memory_test.c     |   2 +-
 .../kvm/x86/private_mem_conversions_test.c    |  55 +-
 .../kvm/x86/private_mem_conversions_test.py   | 159 ++++++
 .../kvm/x86/private_mem_kvm_exits_test.c      |  36 +-
 virt/kvm/Kconfig                              |   4 +-
 virt/kvm/guest_memfd.c                        | 414 +++++++++++++--
 virt/kvm/kvm_main.c                           | 104 +++-
 24 files changed, 1554 insertions(+), 185 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

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2.51.0.858.gf9c4a03a3a-goog