dma-direct: Fix missing sg_dma_len assignment in P2PDMA bus mappings

[ Upstream commit d0d08f4bd7f667dc7a65cd7133c0a94a6f02aca3 ]

Prior to commit a25e7962db0d7 ("PCI/P2PDMA: Refactor the p2pdma mapping
helpers"), P2P segments were mapped using the pci_p2pdma_map_segment()
helper. This helper was responsible for populating sg->dma_address,
marking the bus address, and also setting sg_dma_len(sg).

The refactor[1] removed this helper and moved the mapping logic directly
into the callers. While iommu_dma_map_sg() was correctly updated to set
the length in the new flow, it was missed in dma_direct_map_sg().

Thus, in dma_direct_map_sg(), the PCI_P2PDMA_MAP_BUS_ADDR case sets the
dma_address and marks the segment, but immediately executes 'continue',
which causes the loop to skip the standard assignment logic at the end:

    sg_dma_len(sg) = sg->length;

As a result, when CONFIG_NEED_SG_DMA_LENGTH is enabled, the dma_length
field remains uninitialized (zero) for P2P bus address mappings. This
breaks upper-layer drivers (for e.g. RDMA/IB) that rely on sg_dma_len()
to determine the transfer size.

Fix this by explicitly setting the DMA length in the
PCI_P2PDMA_MAP_BUS_ADDR case before continuing to the next scatterlist
entry.

Fixes: a25e7962db0d7 ("PCI/P2PDMA: Refactor the p2pdma mapping helpers")
Reported-by: Jacob Moroni <jmoroni@google.com>
Signed-off-by: Pranjal Shrivastava <praan@google.com>
[1]
https://lore.kernel.org/all/ac14a0e94355bf898de65d023ccf8a2ad22a3ece.1746424934.git.leon@kernel.org/

Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Shivaji Kant <shivajikant@google.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20251126114112.3694469-1-praan@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 24c359d9c8799fd7d71b34ad1e42ad3cf1f744c7..95f37028032df0bd276c3eb26c1c93d814f807db 100644 (file)
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -486,6 +486,7 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
                case PCI_P2PDMA_MAP_BUS_ADDR:
                        sg->dma_address = pci_p2pdma_bus_addr_map(&p2pdma_state,
                                        sg_phys(sg));
+                       sg_dma_len(sg) = sg->length;
                        sg_dma_mark_bus_address(sg);
                        continue;
                default: