linux-kernel - Re: [PATCH] net/mlx5e: don't assume psp tx skbs are ipv6 csum handling

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Message-ID: <dddaf1c5923576042112c2edad2f285306b839cb.camel@nvidia.com>
Date: Mon, 26 Jan 2026 09:15:33 +0000
From: Cosmin Ratiu <cratiu@...dia.com>
To: "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "davem@...emloft.net" <davem@...emloft.net>, Tariq
 Toukan <tariqt@...dia.com>, Rahul Rameshbabu <rrameshbabu@...dia.com>, Raed
 Salem <raeds@...dia.com>, Mark Bloch <mbloch@...dia.com>, "kuba@...nel.org"
	<kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>, "leon@...nel.org"
	<leon@...nel.org>, Saeed Mahameed <saeedm@...dia.com>, Boris Pismenny
	<borisp@...dia.com>, "daniel.zahka@...il.com" <daniel.zahka@...il.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net/mlx5e: don't assume psp tx skbs are ipv6 csum
 handling

On Fri, 2026-01-23 at 10:11 -0800, Daniel Zahka wrote:
> 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@...il.com>
> ---
> 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
> ---
>  .../net/ethernet/mellanox/mlx5/core/en_accel/psp_rxtx.c   | 15
> +++++++++++----
>  1 file changed, 11 insertions(+), 4 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..15a344ad471d 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
> @@ -178,7 +178,9 @@ 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;
> +	const struct iphdr *ip;
>  	struct tcphdr *th;
> +	int len;

All four of these should be declared lower down in their respective if
branches.

>  
>  	if (!mlx5e_psp_set_state(priv, skb, psp_st))
>  		return true;
> @@ -190,11 +192,16 @@ 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);
> -
> -		th->check = ~tcp_v6_check(skb_shinfo(skb)->gso_size
> + inner_tcp_hdrlen(skb), &ip6->saddr,
> -					  &ip6->daddr, 0);
> +		len = skb_shinfo(skb)->gso_size +
> inner_tcp_hdrlen(skb);
> +
> +		if (skb->protocol == htons(ETH_P_IP)) {
> +			ip = ip_hdr(skb);
> +			th->check = ~tcp_v4_check(len, ip->saddr,
> ip->daddr, 0);
> +		} else {
> +			ip6 = ipv6_hdr(skb);
> +			th->check = ~tcp_v6_check(len, &ip6->saddr,
> &ip6->daddr, 0);
> +		}
>  	}
>  
>  	return true;
> 
> ---
> base-commit: 4a3dba48188208e4f66822800e042686784d29d1
> change-id: 20260122-dzahka-fix-tx-csum-partial-952e8dc28375
> 
> Best regards,

Otherwise LGTM!

Cosmin.