On Mon, Jul 28, 2025 at 10:12:31AM -0600, Logan Gunthorpe wrote:
>
>
> On 2025-07-27 13:05, Jason Gunthorpe wrote:
> > On Fri, Jul 25, 2025 at 10:30:46AM -0600, Logan Gunthorpe wrote:
> >>
> >>
> >> On 2025-07-24 02:13, Leon Romanovsky wrote:
> >>> On Thu, Jul 24, 2025 at 10:03:13AM +0200, Christoph Hellwig wrote:
> >>>> On Wed, Jul 23, 2025 at 04:00:06PM +0300, Leon Romanovsky wrote:
> >>>>> From: Leon Romanovsky <leo...@nvidia.com>
> >>>>>
> >>>>> Export the pci_p2pdma_map_type() function to allow external modules
> >>>>> and subsystems to determine the appropriate mapping type for P2PDMA
> >>>>> transfers between a provider and target device.
> >>>>
> >>>> External modules have no business doing this.
> >>>
> >>> VFIO PCI code is built as module. There is no way to access PCI p2p code
> >>> without exporting functions in it.
> >>
> >> The solution that would make more sense to me would be for either
> >> dma_iova_try_alloc() or another helper in dma-iommu.c to handle the
> >> P2PDMA case.
> >
> > This has nothing to do with dma-iommu.c, the decisions here still need
> > to be made even if dma-iommu.c is not compiled in.
>
> Doesn't it though? Every single call in patch 10 to the newly exported
> PCI functions calls into the the dma-iommu functions. If there were
> non-iommu paths then I would expect the code would use the regular DMA
> api directly which would then call in to dma-iommu.
If p2p type is PCI_P2PDMA_MAP_BUS_ADDR, there will no dma-iommu and DMA
at all.
+static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
+ struct dma_buf_attachment *attachment)
+{
+ struct vfio_pci_dma_buf *priv = dmabuf->priv;
+
+ if (!attachment->peer2peer)
+ return -EOPNOTSUPP;
+
+ if (priv->revoked)
+ return -ENODEV;
+
+ switch (pci_p2pdma_map_type(priv->vdev->provider, attachment->dev)) {
+ case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
+ break;
+ case PCI_P2PDMA_MAP_BUS_ADDR:
+ /*
+ * There is no need in IOVA at all for this flow.
+ * We rely on attachment->priv == NULL as a marker
+ * for this mode.
+ */
+ return 0;
+ default:
+ return -EINVAL;
+ }
+
+ attachment->priv = kzalloc(sizeof(struct dma_iova_state), GFP_KERNEL);
+ if (!attachment->priv)
+ return -ENOMEM;
+
+ dma_iova_try_alloc(attachment->dev, attachment->priv, 0,
priv->phys_vec.len);
+ return 0;
+}
