netdev - [PATCH v3 net-next 2/3] net: hns3/mls5e: fix CWR handling in drivers to preserve ACE signal

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Message-Id: <20260203161126.2436-3-chia-yu.chang@nokia-bell-labs.com>
Date: Tue,  3 Feb 2026 17:11:25 +0100
From: chia-yu.chang@...ia-bell-labs.com
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Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH v3 net-next 2/3] net: hns3/mls5e: fix CWR handling in drivers to preserve ACE signal

From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>

Currently, hns3 and mlx5 Rx paths use 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
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 ensure that RFC3168 ECN offload will
not clear the CWR flag, therefore preserving the ACE signal.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>

---
v3:
- Rewrite the commit message for clarity
---
 drivers/net/ethernet/hisilicon/hns3/hns3_enet.c | 2 +-
 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
index a47464a22751..3a1cf4335477 100644
--- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
+++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
@@ -3897,7 +3897,7 @@ static int hns3_gro_complete(struct sk_buff *skb, u32 l234info)
 
 	skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
 	if (th->cwr)
-		skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
+		skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ACCECN;
 
 	if (l234info & BIT(HNS3_RXD_GRO_FIXID_B))
 		skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_FIXEDID;
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 1fc3720d2201..d174f83478a3 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -1311,7 +1311,7 @@ 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;
 }
 
 static void mlx5e_shampo_update_ipv6_tcp_hdr(struct mlx5e_rq *rq, struct ipv6hdr *ipv6,
@@ -1332,7 +1332,7 @@ static void mlx5e_shampo_update_ipv6_tcp_hdr(struct mlx5e_rq *rq, struct ipv6hdr
 	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;
 }
 
 static void mlx5e_shampo_update_hdr(struct mlx5e_rq *rq, struct mlx5_cqe64 *cqe, bool match)
-- 
2.34.1