netdev - Re: [PATCH net-next v2 1/3] net: gso: do not include jumbogram HBH header in seglen calculation

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Message-ID: <CACGkMEubbV8Pe7w7weke_RZqdYR3U+wrC2iKV5_RXCAfwFw9Jg@mail.gmail.com>
Date: Wed, 14 Jan 2026 11:47:45 +0800
From: Jason Wang <jasowang@...hat.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Mariusz Klimek <maklimek97@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 1/3] net: gso: do not include jumbogram HBH
 header in seglen calculation

On Tue, Jan 13, 2026 at 9:51 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On 1/13/26 9:40 AM, Paolo Abeni wrote:
> > On 1/6/26 10:52 AM, Mariusz Klimek wrote:
> >> @@ -177,8 +178,13 @@ static unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
> >>   */
> >>  static unsigned int skb_gso_network_seglen(const struct sk_buff *skb)
> >>  {
> >> -    unsigned int hdr_len = skb_transport_header(skb) -
> >> -                           skb_network_header(skb);
> >> +    unsigned int off = skb_network_offset(skb) + sizeof(struct ipv6hdr);
> >> +    unsigned int hdr_len = skb_network_header_len(skb);
> >> +
> >> +    /* Jumbogram HBH header is removed upon segmentation. */
> >> +    if (skb_protocol(skb, true) == htons(ETH_P_IPV6) &&
> >> +        skb->len - off > IPV6_MAXPLEN)
> >> +            hdr_len -= sizeof(struct hop_jumbo_hdr);
> >
> > IIRC there is some ongoing discussion about introducing big tcp support
> > for virtio. Perhaps a DEBUG_NET_WARN_ON_ONCE(SKB_GSO_DODGY) could help
> > keeping this check updated at due time?
> >
> > @Jason: could you please double check if I'm off WRT virtio support for
> > big TCP?
>
> Reconsidering the above, I think the mentioned check could be added
> separately, if and when virtio big TCP will come to life.

I agree. BIG TCP support for virtio requires spec features like
tso_max_size/segs advertisement, jumbogram head flags. And if I am not
wrong, HBH header is probably not needed at that time.

Thanks

>
> /P
>