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: <a9dcc27d-521e-44b0-b399-c353ef50077a@redhat.com>
Date: Tue, 13 Jan 2026 09:40:20 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Mariusz Klimek <maklimek97@...il.com>, netdev@...r.kernel.org,
 Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH net-next v2 1/3] net: gso: do not include jumbogram HBH
 header in seglen calculation

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?

/P