Re: [PATCH v8 6/9] vfio/pci: Convert BAR mmap() to use a DMABUF

[sashiko-bot@kernel.org]

> Convert the VFIO device fd fops->mmap to create a DMABUF representing
> the BAR mapping, and make the VMA fault handler look up PFNs from the
> corresponding DMABUF.  This supports future code mmap()ing BAR
> DMABUFs, and iommufd work to support Type1 P2P.
> 
> First, vfio_pci_core_mmap() uses the new
> vfio_pci_core_mmap_prep_dmabuf() helper to export a DMABUF
> representing a single BAR range.  Then, the vfio_pci_mmap_huge_fault()
> callback is updated to understand revoked buffers, and uses the new
> vfio_pci_dma_buf_find_pfn() helper to determine the PFN for a given
> fault address.
> 
> Now that the VFIO DMABUFs can be mmap()ed, vfio_pci_dma_buf_move()
> zaps PTEs (used on the revocation and cleanup paths).
> 
> CONFIG_VFIO_PCI_CORE now unconditionally selects
> CONFIG_DMA_SHARED_BUFFER.  The CONFIG_VFIO_PCI_DMABUF feature
> conditionally includes support for VFIO_DEVICE_FEATURE_DMA_BUF,
> depending on the availability of CONFIG_PCI_P2PDMA.
> 
> When the DMABUF feature is not present, DMABUFs are used internally
> for the BAR mappings.  In this case, DMABUF attach is prohibited (and
> the requirement for a P2PDMA provider is relaxed).
> 
> 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=6