On Thu, Sep 16, 2021 at 05:40:44PM -0600, Logan Gunthorpe wrote: > Add pci_p2pdma_map_segment() as a helper for simple dma_map_sg() > implementations. It takes an scatterlist segment that must point to a > pci_p2pdma struct page and will map it if the mapping requires a bus > address. > > The return value indicates whether the mapping required a bus address > or whether the caller still needs to map the segment normally. If the > segment should not be mapped, -EREMOTEIO is returned. > > This helper uses a state structure to track the changes to the > pgmap across calls and avoid needing to lookup into the xarray for > every page. > > Also add pci_p2pdma_map_bus_segment() which is useful for IOMMU > dma_map_sg() implementations where the sg segment containing the page > differs from the sg segment containing the DMA address. > > Signed-off-by: Logan Gunthorpe <[email protected]> > drivers/pci/p2pdma.c | 59 ++++++++++++++++++++++++++++++++++++++ > include/linux/pci-p2pdma.h | 21 ++++++++++++++ > 2 files changed, 80 insertions(+) > > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index b656d8c801a7..58c34f1f1473 100644 > +++ b/drivers/pci/p2pdma.c > @@ -943,6 +943,65 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev, > struct scatterlist *sg, > } > EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs); > > +/** > + * pci_p2pdma_map_segment - map an sg segment determining the mapping type > + * @state: State structure that should be declared outside of the > for_each_sg() > + * loop and initialized to zero. > + * @dev: DMA device that's doing the mapping operation > + * @sg: scatterlist segment to map > + * > + * This is a helper to be used by non-iommu dma_map_sg() implementations > where > + * the sg segment is the same for the page_link and the dma_address. > + * > + * Attempt to map a single segment in an SGL with the PCI bus address. > + * The segment must point to a PCI P2PDMA page and thus must be > + * wrapped in a is_pci_p2pdma_page(sg_page(sg)) check. > + * > + * Returns the type of mapping used and maps the page if the type is > + * PCI_P2PDMA_MAP_BUS_ADDR. > + */ > +enum pci_p2pdma_map_type > +pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device > *dev, > + struct scatterlist *sg) > +{ > + if (state->pgmap != sg_page(sg)->pgmap) { > + state->pgmap = sg_page(sg)->pgmap; > + state->map = pci_p2pdma_map_type(state->pgmap, dev); > + state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset; > + }
Is this safe? I was just talking with Joao about this, https://lore.kernel.org/r/[email protected] API wise I absolutely think this should be safe as written, but is it really? Does pgmap ensure that a positive refcount struct page always has a valid pgmap pointer (and thus the mess in gup can be deleted) or does this need to get the pgmap as well to keep it alive? Jason _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
