Re: [PATCH v11 3/4] vfio/pci: implement get_pci_tph and DMA_BUF_TPH feature

[sashiko-bot@kernel.org]

> Implement dma-buf get_pci_tph for vfio-pci exported dma-bufs and add
> VFIO_DEVICE_FEATURE_DMA_BUF_TPH so userspace can publish TPH metadata
> for a VFIO-owned device.
> 
> 8-bit ST and 16-bit Extended ST are distinct PCIe TPH namespaces; the
> uAPI carries both with explicit validity flags, and get_pci_tph()
> returns the value matching the importer's requested namespace or
> -EOPNOTSUPP.
> 
> Publish and read the TPH descriptor under dmabuf->resv, matching the
> locking used for other importer-visible dma-buf state. The SET ioctl
> takes dma_resv_lock_interruptible(), while the callback runs under
> DMA-buf's asserted resv lock.
> 
> The attach path reads @revoked without holding memory_lock. Annotate it
> with READ_ONCE() to document this intentional lockless access: the read
> is a benign early-out, and a racing revocation is re-checked under
> dmabuf->resv in vfio_pci_dma_buf_map() before any mapping is handed out.
> The annotation only needs to keep the access well-formed against the
> memory_lock-protected writers.
> 
> Reject requests the device cannot consume as a completer:
> pcie_tph_completer_type() must report at least
> PCI_EXP_DEVCAP2_TPH_COMP_TPH_ONLY, and Extended ST requires
> PCI_EXP_DEVCAP2_TPH_COMP_EXT_TPH. Make PROBE follow the same hardware
> gate so the feature only probes as supported when the device can really
> consume it.
> 
> Signed-off-by: Zhiping Zhang <zhipingz@meta.com>

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

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260702181025.2694961-1-zhipingz@meta.com?part=3