Re: [PATCH net v3 1/4] net/mlx5e: psp: tso: replace only the length in checksum seed

[sashiko-bot@kernel.org]

> for psp tcp with tso,
> 
>  - __tcp_transmit_skb() -> tcp_v6_send_check() or tcp_v4_send_check()
>    computes the checksum seed using the addresses on the socket and the
>    total length, then
> 
>  - mlx5e_psp_handle_tx_skb() recomputes the checksum seed using
>    addresses from the packet's l3 header, and the length of one segment
> 
> the length difference is expected by the device. however, the
> difference in addresses is incorrect in cases where the l3 header daddr
> is an intermediate hop (e.g. IPV6_RTHDR). this causes every segment of
> the tso packet to go out with a bad tcp checksum, in this case.
> 
> the fix is to replace only the length in the seed which tcp had already
> computed. this is also what tcp_gso_segment() does.
> 
> tested on connectx-7 with the rest of this series applied, with a psp
> tcp socket whose segment routing header's first hop isn't the final
> destination, and the peer checking tcp checksums in software.
> 
> Fixes: e5a1861a298e ("net/mlx5e: Implement PSP Tx data path")
> Signed-off-by: Todd Freed <toddfreed@meta.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261023234640.1459291-1-toddfreed@meta.com?part=1