Re: [PATCH v8 8/9] vfio/pci: Support mmap() of a VFIO DMABUF

[sashiko-bot@kernel.org]

> A VFIO DMABUF can export a subset of a BAR to userspace by fd; add
> support for mmap() of this fd.  This provides another route for a
> process to map BARs, in which the process can only map a specific
> subset of a BAR represented by the exported DMABUF.
> 
> mmap() support enables userspace drivers to safely delegate BAR
> sub-ranges to other processes by sharing a DMABUF fd, without having
> to share the (omnipotent) VFIO device fd with them.
> 
> Since the main VFIO BAR mmap() is now DMABUF-aware, the new mmap() reuses
> the existing vm_ops.
> 
> The lifecycle of an exported DMABUF remains decoupled from that of the
> device fd it came from, i.e. the device fd could be closed with DMABUF
> VMAs present, meaning a fault on a VMA could happen concurrently with
> vfio_pci_dma_buf_cleanup().
> 
> To deal with this scenario, the fault handler now temporarily takes a
> VFIO device registration to ensure the vdev remains valid, and then
> vdev locks can be taken.
> 
> Signed-off-by: Matt Evans <matt@ozlabs.org>

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

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Sashiko AI review · https://sashiko.dev/#/patchset/20261006193643.76330-1-matt@ozlabs.org?part=8