[PATCH v4 1/9] block: add BLK_STS_P2PDMA for unsupported peer-to-peer transfers

[Mykola Marzhan]

From: Logan Gunthorpe <logang at deltatee.com>

blk_dma_map_iter_start() reports BLK_STS_INVAL when a P2PDMA transfer
is attempted between two devices whose PCIe topology cannot route it.
blk_path_error() treats INVAL as retryable, so multipath requeues the
I/O forever, and callers cannot tell it apart from an invalid request.
md also ignores it for member failures, so a mirror silently diverges.

Restoring the old BLK_STS_TARGET would stay ambiguous -- nvme maps
NS_NOT_READY, LBA_RANGE and CMD_INTERRUPTED to it too.  Add a dedicated
BLK_STS_P2PDMA, non-retryable in blk_path_error(), and return it from
blk_dma_map_iter_start().

Fixes: 858299dc6160 ("block: add scatterlist-less DMA mapping helpers")
Fixes: 7ce3c1dd78fc ("nvme-pci: convert the data mapping to blk_rq_dma_map")
Cc: stable at vger.kernel.org # v6.17
Signed-off-by: Logan Gunthorpe <logang at deltatee.com>
Signed-off-by: Mykola Marzhan <mykola at meshstor.io>
---
 block/blk-core.c          |  3 +++
 block/blk-mq-dma.c        |  3 ++-
 include/linux/blk_types.h | 10 ++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 365641266c9e..83cb5464265f 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -177,6 +177,9 @@ static const struct {
 
 	/* Command duration limit device-side timeout */
 	ENT(DURATION_LIMIT,	-ETIME,		"duration limit exceeded"),
+
+	/* no PCIe P2PDMA route between initiator and target */
+	ENT(P2PDMA,		-EREMOTEIO,	"peer-to-peer transfer unroutable"),
 	ENT(INVAL,		-EINVAL,	"invalid"),
 
 	/* everything else not covered above: */
diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
index bfdb9ed70741..e88d6b3524e6 100644
--- a/block/blk-mq-dma.c
+++ b/block/blk-mq-dma.c
@@ -189,8 +189,9 @@ static bool blk_dma_map_iter_start(struct request *req, struct device *dma_dev,
 		 */
 	case PCI_P2PDMA_MAP_NONE:
 		break;
+	case PCI_P2PDMA_MAP_NOT_SUPPORTED:
 	default:
-		iter->status = BLK_STS_INVAL;
+		iter->status = BLK_STS_P2PDMA;
 		return false;
 	}
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 8808ee76e73c..c8de7809320a 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -165,6 +165,15 @@ typedef u16 blk_short_t;
  */
 #define BLK_STS_DURATION_LIMIT	((__force blk_status_t)17)
 
+/*
+ * BLK_STS_P2PDMA is returned when a peer-to-peer DMA transfer cannot be
+ * mapped (typically because there is no route between the initiator and the
+ * target that the platform's PCIe topology and ACS settings allow). This
+ * is a property of the initiator/target pair, not of the target device's
+ * health. This error should never be retried.
+ */
+#define BLK_STS_P2PDMA	((__force blk_status_t)18)
+
 /*
  * Invalid size or alignment.
  */
@@ -188,6 +197,7 @@ static inline bool blk_path_error(blk_status_t error)
 	case BLK_STS_NOTSUPP:
 	case BLK_STS_NOSPC:
 	case BLK_STS_TARGET:
+	case BLK_STS_P2PDMA:
 	case BLK_STS_RESV_CONFLICT:
 	case BLK_STS_MEDIUM:
 	case BLK_STS_PROTECTION:
-- 
2.52.0