[PATCH v2 0/2] vfio/nvgrace-gpu: Separate the fallback-mode open_device

[Andrea Parri <parri.andrea@gmail.com>]

In fallback mode, where the ACPI memory properties are missing or the
C2C link is down, nvgrace-gpu opens a device through
nvgrace_gpu_open_device() but closes it through
vfio_pci_core_close_device().  The open registers an empty usemem range
for poison handling that nothing unregisters, so a second open fails
with -EBUSY, and the first open after an unbind hits a KASAN
slab-use-after-free in register_pfn_address_space().

Patch 1 gives the fallback table its own open_device, as Alex suggested
on v1, and is marked for stable.  Patch 2 drops a usemem length check
in nvgrace_gpu_open_device() that only existed for fallback mode.

Tested on x86-64 under virtme-ng with KASAN, not on Grace hardware.  A
QEMU cxl-type3 function, bound through driver_override, takes the
fallback path and is opened through a noiommu VFIO cdev.  On v7.3-rc7
the second open fails with -EBUSY and the open after unbind and rebind
reports the use-after-free.  With patch 1, and with the whole series,
neither happens.  Patch 2 only affects full mode, which this setup
cannot reach.

Changes in v2:
- Replace the usemem.memlength guards with a core-only open_device for
  the fallback table (Alex)
- Add patch 2
- Fallback open no longer fails when BAR0 cannot be mapped; Ankit
  confirmed fallback mode does not need that check
- Rebase on v7.3-rc7

v1: https://lore.kernel.org/r/20260925161024.189771-1-parri.andrea@gmail.com/

Andrea Parri (2):
  vfio/nvgrace-gpu: Use a core-only open_device in fallback mode
  vfio/nvgrace-gpu: Drop the usemem length check in open_device

 drivers/vfio/pci/nvgrace-gpu/main.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)


base-commit: 24a19b953e2a3d0ea5a8c4951a0ab8f32720c907
-- 
2.53.0