[PATCH v6 02/12] md: ensure REQ_NOMERGE is set on P2PDMA bios
From: Mykola Marzhan <hidden>
Date: 2026-07-26 11:32:41
Also in:
linux-block, linux-nvme, linux-pci, linux-rdma, lkml, stable
Subsystem:
software raid (multiple disks) support, the rest · Maintainers:
Song Liu, Yu Kuai, Linus Torvalds
md_submit_bio() strips REQ_NOMERGE from every bio. For P2PDMA bios
the flag is what keeps requests single-provider (see
__bio_add_page()): merging a P2PDMA bio with one over a different
pgmap, or over host memory, maps the merged request with the wrong
bus address. Set the flag on P2PDMA bios -- bios built via
bio_iov_bvec_set() arrive without it -- and keep stripping it
otherwise.
Fixes: 02666132403a ("md: propagate BLK_FEAT_PCI_P2PDMA from member devices to RAID device")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Mykola Marzhan <redacted>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
---
drivers/md/md.c | 10 ++++++++--
drivers/md/md.h | 15 +++++++++++++++
2 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index d1465bcd86c8..3770bdb4d4b2 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c@@ -451,8 +451,14 @@ static void md_submit_bio(struct bio *bio) return; } - /* bio could be mergeable after passing to underlayer */ - bio->bi_opf &= ~REQ_NOMERGE; + /* + * A bio md split may merge again below md -- except P2PDMA bios, + * which must stay single-provider (see __bio_add_page()). + */ + if (md_bio_is_p2pdma(bio)) + bio->bi_opf |= REQ_NOMERGE; + else + bio->bi_opf &= ~REQ_NOMERGE; md_handle_request(mddev, bio); }
diff --git a/drivers/md/md.h b/drivers/md/md.h
index d8daf0f75cbb..73df1a6eccd8 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h@@ -11,8 +11,10 @@ #include <linux/blkdev.h> #include <linux/backing-dev.h> #include <linux/badblocks.h> +#include <linux/bio.h> #include <linux/kobject.h> #include <linux/list.h> +#include <linux/memremap.h> #include <linux/mm.h> #include <linux/mutex.h> #include <linux/timer.h>
@@ -22,6 +24,19 @@ #include <trace/events/block.h> #define MaxSector (~(sector_t)0) + +/* + * P2P and host pages never mix within a bio, so the first bvec is + * representative. Read bi_io_vec directly: bio_first_bvec_all() + * WARNs on the split clones md handles, and data-less bios have no + * bi_io_vec. Not valid after the bio's iterator is consumed. + */ +static inline bool md_bio_is_p2pdma(struct bio *bio) +{ + return bio_has_data(bio) && bio->bi_io_vec && + is_pci_p2pdma_page(bio->bi_io_vec->bv_page); +} + /* * Number of guaranteed raid bios in case of extreme VM load: */
--
2.52.0