6.17-stable review patch. If anyone has any objections, please let me know.

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From: Pranjal Shrivastava praan@google.com

[ 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.1746424...

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 --- kernel/dma/direct.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index 24c359d9c8799..95f37028032df 100644 --- 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: