[PATCH v2] net/mlx5: fix lro update tcp header cksum error

[jiangheng (G)]

The variable csum is the sum of three 16 bits integers, the max value
is 0x2FFFD. The corner case of sum of 3 is 0x1FFFF gives the wrong
result: 0x1 + 0xFFFF = 0x10000, the upper 16 bits are not 0.
It must be folded again to ensure that the upper 16 bits are 0.

Fixes: e4c2a16eb1de ("net/mlx5: handle LRO packets in Rx queue")
Cc: stable at dpdk.org

Signed-off-by: jiangheng <jiangheng14 at huawei.com>
---
 drivers/net/mlx5/mlx5_rx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/mlx5/mlx5_rx.c b/drivers/net/mlx5/mlx5_rx.c
index a2be523e9e..ae537dfffa 100644
--- a/drivers/net/mlx5/mlx5_rx.c
+++ b/drivers/net/mlx5/mlx5_rx.c
@@ -1090,6 +1090,7 @@ mlx5_lro_update_tcp_hdr(struct rte_tcp_hdr *__rte_restrict tcp,
 	tcp->cksum = 0;
 	csum += rte_raw_cksum(tcp, (tcp->data_off >> 4) * 4);
 	csum = ((csum & 0xffff0000) >> 16) + (csum & 0xffff);
+	csum = ((csum & 0xffff0000) >> 16) + (csum & 0xffff);
 	csum = (~csum) & 0xffff;
 	if (csum == 0)
 		csum = 0xffff;
-- 
2.27.0

> Hi,  Jiangheng
>
> You are right, the corner case of sum of 3 is 0x1FFFF gives the wrong result.
> Could you,  please, format the patch according to the rules and send v2 ?
> - add Fixes: tag with reference to appropriate commit
> - add Cc: stable at dpdk.org
> - fix typos in commit message - capitalize sentences, add trailing points, etc.
>
> With best regards,
> Slava
>
> > From: jiangheng (G) <jiangheng14 at huawei.com>
> > Sent: среда, 12 апреля 2023 г. 14:39
> > To: dev at dpdk.org; Matan Azrad <matan at nvidia.com>; Slava Ovsiienko 
> > <viacheslavo at nvidia.com>
> > Subject: [PATCH] net/mlx5: fix lro update tcp header cksum error
> > 
> > csum is the sum of three 16 bits value it must be folded twice to 
> > ensure that the upper 16 bits are 0
> > ---
> >  drivers/net/mlx5/mlx5_rx.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/net/mlx5/mlx5_rx.c b/drivers/net/mlx5/mlx5_rx.c 
> > index a2be523e9e..ae537dfffa 100644
> > --- a/drivers/net/mlx5/mlx5_rx.c
> > +++ b/drivers/net/mlx5/mlx5_rx.c
> > @@ -1090,6 +1090,7 @@ mlx5_lro_update_tcp_hdr(struct rte_tcp_hdr 
> > *__rte_restrict tcp,
> >     tcp->cksum = 0;
> >     csum += rte_raw_cksum(tcp, (tcp->data_off >> 4) * 4);
> >     csum = ((csum & 0xffff0000) >> 16) + (csum & 0xffff);
> > +   csum = ((csum & 0xffff0000) >> 16) + (csum & 0xffff);
> >     csum = (~csum) & 0xffff;
> >     if (csum == 0)
> >         csum = 0xffff;
> > --
> > 2.27.0