[PATCH v3 1/8] blk-mq-dma: restore BLK_STS_TARGET for unsupported P2P transfers

[Mykola Marzhan]

Unsupported P2P transfers used to fail with BLK_STS_TARGET, chosen
by commit 91fb2b6052f7 ("nvme-pci: convert to using
dma_map_sgtable()") for dma_map_sgtable()'s -EREMOTEIO: an I/O that
can never succeed on this device must not be retried.  The
blk_rq_dma_map conversion changed it to BLK_STS_INVAL, which
blk_path_error() treats as retryable and md deliberately ignores
for member failures -- a P2P write to a member the peer cannot
reach is counted as written and the mirrors silently diverge.

Restore BLK_STS_TARGET.  Hit e.g. with CMB memory of one NVMe
device used as the data buffer for I/O to a second one behind a
different host bridge.

Fixes: 858299dc6160 ("block: add scatterlist-less DMA mapping helpers")
Fixes: 7ce3c1dd78fc ("nvme-pci: convert the data mapping to blk_rq_dma_map")
Cc: stable@xxxxxxxxxxxxxxx # v6.17
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Mykola Marzhan <mykola@xxxxxxxxxxx>
Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 block/blk-mq-dma.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
index bfdb9ed70741..c17e4c49900c 100644
--- a/block/blk-mq-dma.c
+++ b/block/blk-mq-dma.c
@@ -190,7 +190,11 @@ static bool blk_dma_map_iter_start(struct request *req, struct device *dma_dev,
 	case PCI_P2PDMA_MAP_NONE:
 		break;
 	default:
-		iter->status = BLK_STS_INVAL;
+		/*
+		 * Match dma_map_sgtable()'s -EREMOTEIO: this transfer
+		 * can never succeed, so don't let it be retried.
+		 */
+		iter->status = BLK_STS_TARGET;
 		return false;
 	}
 
-- 
2.52.0