[PATCH v2] net/mlx5e: don't assume psp tx skbs are ipv6 csum handling

[Daniel Zahka]

mlx5e_psp_handle_tx_skb() assumes skbs are ipv6 when doing a partial
TCP checksum with tso. Make correctly mlx5e_psp_handle_tx_skb() handle
ipv4 packets.

Fixes: e5a1861a298e ("net/mlx5e: Implement PSP Tx data path")
Signed-off-by: Daniel Zahka <daniel.zahka@xxxxxxxxx>
---
This is a bug when an ipv4 tx skb passes through
mlx5e_psp_handle_tx_skb() and tso is requested. It was previously
undetected in my testing because my setup involves cx7's on both ends,
and mlx5e_handle_csum() marks PSP rx skb's with csum_unnecessary.

To reproduce the problem just turn off NETIF_F_RXCSUM and observe:
nstat -a | grep TcpInCsumErrors
---
Changes in v2:
- move declarations down into branches where they are used.
- Link to v1: https://lore.kernel.org/r/20260123-dzahka-fix-tx-csum-partial-v1-1-7b0107693883@xxxxxxxxx
---
 .../net/ethernet/mellanox/mlx5/core/en_accel/psp_rxtx.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/psp_rxtx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/psp_rxtx.c
index c17ea0fcd8ef..ef7f5338540f 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/psp_rxtx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/psp_rxtx.c
@@ -177,8 +177,6 @@ bool mlx5e_psp_handle_tx_skb(struct net_device *netdev,
 {
 	struct mlx5e_priv *priv = netdev_priv(netdev);
 	struct net *net = sock_net(skb->sk);
-	const struct ipv6hdr *ip6;
-	struct tcphdr *th;
 
 	if (!mlx5e_psp_set_state(priv, skb, psp_st))
 		return true;
@@ -190,11 +188,18 @@ bool mlx5e_psp_handle_tx_skb(struct net_device *netdev,
 		return false;
 	}
 	if (skb_is_gso(skb)) {
-		ip6 = ipv6_hdr(skb);
-		th = inner_tcp_hdr(skb);
+		int len = skb_shinfo(skb)->gso_size + inner_tcp_hdrlen(skb);
+		struct tcphdr *th = inner_tcp_hdr(skb);
 
-		th->check = ~tcp_v6_check(skb_shinfo(skb)->gso_size + inner_tcp_hdrlen(skb), &ip6->saddr,
-					  &ip6->daddr, 0);
+		if (skb->protocol == htons(ETH_P_IP)) {
+			const struct iphdr *ip = ip_hdr(skb);
+
+			th->check = ~tcp_v4_check(len, ip->saddr, ip->daddr, 0);
+		} else {
+			const struct ipv6hdr *ip6 = ipv6_hdr(skb);
+
+			th->check = ~tcp_v6_check(len, &ip6->saddr, &ip6->daddr, 0);
+		}
 	}
 
 	return true;

---
base-commit: 709bbb015538dfd5c97308b77c950d41a4d95cd3
change-id: 20260122-dzahka-fix-tx-csum-partial-952e8dc28375

Best regards,
-- 
Daniel Zahka <daniel.zahka@xxxxxxxxx>