netdev - [PATCH net 1/1] net/rds: dma_map_sg is entitled to merge entries

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Message-ID: <60efc69f-1f35-529d-a7ef-da0549cad143@oracle.com>
Date:   Tue, 17 Aug 2021 10:04:37 -0700
From:   Gerd Rausch <gerd.rausch@...cle.com>
To:     Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, rds-devel@....oracle.com
Subject: [PATCH net 1/1] net/rds: dma_map_sg is entitled to merge entries

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 <gerd.rausch@...cle.com>
---
 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 9b6ffff72f2d..28c1b0022178 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,
-- 
2.24.1