Re: [PATCH v8 1/9] vfio/pci: Remove DMABUF export dependency on vdev->memory_lock

[sashiko-bot@kernel.org]

> The VFIO_DEVICE_FEATURE_DMA_BUF export previously used
> vdev->memory_lock to protect VFIO's list of exported DMABUFs
> (vdev->dmabufs) and their revocation status.  When adding a new
> export, memory_lock was taken for write.
> 
> A future commit will refactor DMABUF export into a function used from
> mmap(), which would create a new mmap_lock -> memory_lock dependency.
> 
> In preparation, this commit introduces a vdev->dmabuf_lock that
> protects the dmabufs list, per-DMABUF revocation state, and a new
> bars_revoked flag.  The flag tracks the device-wide BAR revocation
> state set via vfio_pci_dma_buf_move() under dmabuf_lock, removing the
> test of __vfio_pci_memory_enabled() and dependency on
> vdev->memory_lock.
> 
> This is a cleanup currently, but allows the future export path to
> avoid holding memory_lock under mmap_lock and a therefore avoid a
> deadlock scenario (a fault handler attempting to take mmap_lock in a
> vfio-pci variant driver thread that holds memory_lock, vs another
> thread doing an mmap/export holding them both in the other order).
> 
> Signed-off-by: Matt Evans <matt@ozlabs.org>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261006193643.76330-1-matt@ozlabs.org?part=1