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: <55e12beb-758c-4f82-992e-e07c9c300d4b@redhat.com>
Date: Tue, 13 Jan 2026 14:51:08 +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 1/13/26 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.

/P