[PATCH v3 0/3] vfio/pci: fix huge_fault write handling and add selftest

[Mina Almasry <almasrymina@google.com>]

Fix vfio_pci_vmf_insert_pfn() passing write=false to
vmf_insert_pfn_pmd() and vmf_insert_pfn_pud(), which causes an infinite
write page-fault loop when vma->vm_page_prot starts read-only (such as
after soft-dirty clearing via /proc/<pid>/clear_refs in CRIU or live
migration, or on arm64 without hardware DBM), and add a companion VFIO
PCI selftest covering both read-then-write upgrade and initial write
faults after clear_refs.

Changes in v3:
- Add Patch 2/3 introducing vfio_pci_find_mem_bar() in libvfio to locate
  a memory-backed BAR (or range within a BAR) from a table of known
  devices (starting with QEMU's pci-testdev 1b36:0005 BAR 2), per David
  Matlack.
- Update Patch 3/3 (bar_write_fault_after_clear_refs) to require a known
  memory-backed BAR >= SZ_2M via vfio_pci_find_mem_bar(), zap BAR
  mappings via PCI_COMMAND_MEMORY before both sub-tests instead of
  re-mmapping (addressing both David Matlack's and Sashiko's feedback),
  and leave PCI_COMMAND_MEMORY enabled afterward.
- Link to v2: https://lore.kernel.org/all/20261101062049.998160-1-almasrymina@google.com/

Changes in v2:
- Expand Patch 1/2 commit log with practical trigger scenarios (CRIU /
  clear_refs soft-dirty clearing and arm64 software dirty tracking) for
  stable backport evaluation, per Alex Williamson.
- Drop the Assisted-by tag from Patch 1/2.
- Add Patch 2/2 selftest in vfio_pci_device_test (bar_write_fault_after_clear_refs),
  as suggested by Alex Williamson.
- Link to v1: https://lore.kernel.org/all/20261024015540.538758-1-almasrymina@google.com/

Mina Almasry (3):
  vfio/pci: pass FAULT_FLAG_WRITE to vmf_insert_pfn_pmd/pud()
  vfio: selftests: Add vfio_pci_find_mem_bar() helper
  vfio: selftests: Test BAR write faults after clear_refs

 drivers/vfio/pci/vfio_pci_core.c              |  6 +-
 .../lib/include/libvfio/vfio_pci_device.h     | 10 +++
 .../selftests/vfio/lib/vfio_pci_device.c      | 67 +++++++++++++++++++
 .../selftests/vfio/vfio_pci_device_test.c     | 65 ++++++++++++++++++
 4 files changed, 146 insertions(+), 2 deletions(-)


base-commit: 076d7e989cb69f6ded7d60f2a080eb909930061b
-- 
2.56.0.385.gac671c819a-goog