Re: [PATCH v4 net 3/3] net: hns3: fix CWR handling in drivers to preserve ACE signal

[Jijie Shao <shaojijie@huawei.com>]

on 2026/4/17 23:26, chia-yu.chang@nokia-bell-labs.com wrote:
> From: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
>
> Currently, hns3 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.
>
> Fixes: d474d88f88261 ("net: hns3: add hns3_gro_complete for HW GRO process")
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
> ---
>   drivers/net/ethernet/hisilicon/hns3/hns3_enet.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
> index a3206c97923e..e1b0dba56182 100644
> --- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
> @@ -3904,7 +3904,7 @@ 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;

I agree with Paolo's previous point;
for already released hardware, it is indeed not suitable to modify it.
During the hardware aggregation process, the ACE signal may have already been lost.

Jijie Shao