Subject: [PATCH AUTOSEL 5.4 10/10] net/rds: dma_map_sg is entitled to merge entries

From: Sasha Levin <[email-masked]>
Date: Mon, 23 Aug 2021 20:54:57 -0400

From: Gerd Rausch <[email-masked]>

[ Upstream commit fb4b1373dcab086d0619c29310f0466a0b2ceb8a ]

Function "dma_map_sg" is entitled to merge adjacent entries
and return a value smaller than what was passed as "nents".

Subsequently "ib_map_mr_sg" needs to work with this value ("sg_dma_len")
rather than the original "nents" parameter ("sg_len").

This old RDS bug was exposed and reliably causes kernel panics
(using RDMA operations "rds-stress -D") on x86_64 starting with:
commit c588072bba6b ("iommu/vt-d: Convert intel iommu driver to the iommu ops")

Simply put: Linux 5.11 and later.

Signed-off-by: Gerd Rausch <[email-masked]>
Acked-by: Santosh Shilimkar <[email-masked]>
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Jakub Kicinski <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 net/rds/ib_frmr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/rds/ib_frmr.c b/net/rds/ib_frmr.c
index 06ecf9d2d4bf..ef6acd721118 100644
--- a/net/rds/ib_frmr.c
+++ b/net/rds/ib_frmr.c
@@ -131,9 +131,9 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)
 		cpu_relax();
 	}
 
-	ret = ib_map_mr_sg_zbva(frmr->mr, ibmr->sg, ibmr->sg_len,
+	ret = ib_map_mr_sg_zbva(frmr->mr, ibmr->sg, ibmr->sg_dma_len,
 				&off, PAGE_SIZE);
-	if (unlikely(ret != ibmr->sg_len))
+	if (unlikely(ret != ibmr->sg_dma_len))
 		return ret < 0 ? ret : -EINVAL;
 
 	if (cmpxchg(&frmr->fr_state,
-- 
2.30.2