[PATCH RFC v3 0/4] guest_memfd: Track amount of memory allocated on inode

[Ackerley Tng]

Hi,

Currently, guest_memfd doesn't update inode's i_blocks or i_bytes at
all. Hence, st_blocks in the struct populated by a userspace fstat()
call on a guest_memfd will always be 0. This patch series makes
guest_memfd track the amount of memory allocated on an inode, which
allows fstat() to accurately report that on requests from userspace.

The inode's i_blocks and i_bytes fields are updated when the folio is
associated or disassociated from the guest_memfd inode, which are at
allocation and truncation times respectively.

RFC v3 uses the .invalidate_folio() callback to update accounting in inode
fields at truncation time, and sets AS_RELEASE_ALWAYS for guest_memfd
mappings to enable .invalidate_folio() for guest_memfd.

RFC v3 series is based on kvm-x86/next.

+ RFC v2: Removed a full custom implementation of .evict_inode for
  guest_memfd in favor of adding .unaccount_folio callback.
  + https://lore.kernel.org/all/20260225-gmem-st-blocks-v2-0-87d7098119a9@xxxxxxxxxx/T/
+ RFC v1: https://lore.kernel.org/all/cover.1771826352.git.ackerleytng@xxxxxxxxxx/T/

Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
Ackerley Tng (4):
      KVM: guest_memfd: Track amount of memory allocated on inode
      KVM: guest_memfd: Set release always on guest_memfd mappings
      KVM: selftests: Wrap fstat() to assert success
      KVM: selftests: Test that st_blocks is updated on allocation

 tools/testing/selftests/kvm/guest_memfd_test.c     | 32 +++++++++++++++-------
 tools/testing/selftests/kvm/include/kvm_syscalls.h |  2 ++
 virt/kvm/guest_memfd.c                             | 15 ++++++++++
 3 files changed, 39 insertions(+), 10 deletions(-)
---
base-commit: 5128b972fb2801ad9aca54d990a75611ab5283a9
change-id: 20260225-gmem-st-blocks-733f35d10211

Best regards,
--
Ackerley Tng <ackerleytng@xxxxxxxxxx>