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Thu, 23 Apr 2026 00:30:50 -0700 (PDT) Received: from [192.168.88.32] ([150.228.93.216]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4896c2a1804sm126727665e9.4.2026.04.23.00.30.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Apr 2026 00:30:49 -0700 (PDT) Message-ID: <69750ae3-3b0f-41c7-9731-6d49f5f6d319@redhat.com> Date: Thu, 23 Apr 2026 09:30:47 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 net 2/3] net: mlx5e: fix CWR handling in drivers to preserve ACE signal To: chia-yu.chang@nokia-bell-labs.com, linyunsheng@huawei.com, andrew+netdev@lunn.ch, parav@nvidia.com, jasowang@redhat.com, mst@redhat.com, shenjian15@huawei.com, salil.mehta@huawei.com, shaojijie@huawei.com, saeedm@nvidia.com, tariqt@nvidia.com, mbloch@nvidia.com, leonro@nvidia.com, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, horms@kernel.org, ij@kernel.org, ncardwell@google.com, koen.de_schepper@nokia-bell-labs.com, g.white@cablelabs.com, ingemar.s.johansson@ericsson.com, mirja.kuehlewind@ericsson.com, cheshire@apple.com, rs.ietf@gmx.at, Jason_Livingood@comcast.com, vidhi_goel@apple.com References: <20260417152642.71674-1-chia-yu.chang@nokia-bell-labs.com> <20260417152642.71674-3-chia-yu.chang@nokia-bell-labs.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20260417152642.71674-3-chia-yu.chang@nokia-bell-labs.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/17/26 5:26 PM, chia-yu.chang@nokia-bell-labs.com wrote: > From: Chia-Yu Chang > > Currently, mlx5 Rx paths use the SKB_GSO_TCP_ECN flag when a TCP segment > with the CWR flag set. This is wrong because SKB_GSO_TCP_ECN is only > valid for RFC3168 ECN on Tx, and using it on Rx allows RFC3168 ECN > offload to clear the CWR flag. As a result, incoming TCP segments > may lose their ACE signal integrity required for AccECN (RFC9768), > especially when the packet is forwarded and later re-segmented by GSO. > > Fix this by setting SKB_GSO_TCP_ACCECN for any Rx segment with the CWR > flag set. SKB_GSO_TCP_ACCECN ensures that RFC3168 ECN offload will > not clear the CWR flag, therefore preserving the ACE signal. > > Fixes: 92552d3abd329 ("net/mlx5e: HW_GRO cqe handler implementation") > Signed-off-by: Chia-Yu Chang > --- > drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > index 5b60aa47c75b..9b1c80079532 100644 > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > @@ -1180,7 +1180,7 @@ static void mlx5e_shampo_update_ipv4_tcp_hdr(struct mlx5e_rq *rq, struct iphdr * > skb->csum_offset = offsetof(struct tcphdr, check); > > if (tcp->cwr) > - skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN; > + skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ACCECN; Here there is an open question for nVidia: Is the above enough or will later segmentation lead to the wrong results? I think/guess the firmware is (still) aggregating the wire frames using the ECN schema, i.e. the first wire packet has CWR == 1, the later CWR==0. If so, later segmentation of this GSO packet will emit CWR == 1 on all the packets, making the egress stream different from ingress. @Saeed, Leon, Tariq: could you please have a look here? I guess that with a more conservative approach drivers update should be omitted, and the updated documentation should be less forceful (i.e. "TCP_ECN should not be used in RX") /P Thanks, Paolo