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net: Enable BIG TCP with partial GSO

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skb_segment is called for partial GSO, when netif_needs_gso returns true
in validate_xmit_skb. Partial GSO is needed, for example, when
segmentation of tunneled traffic is offloaded to a NIC that only
supports inner checksum offload.

Currently, skb_segment clamps the segment length to 65534 bytes, because
gso_size == 65535 is a special value GSO_BY_FRAGS, and we don't want
to accidentally assign mss = 65535, as it would fall into the
GSO_BY_FRAGS check further in the function.

This implementation, however, artificially blocks len > 65534, which is
possible since the introduction of BIG TCP. To allow bigger lengths and
avoid resegmentation of BIG TCP packets, store the gso_by_frags flag in
the beginning and don't use a special value of mss for this purpose
after mss was modified.

Signed-off-by: Alice Mikityanska <alice@isovalent.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260710134242.216538-3-alice.kernel@fastmail.im
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Alice Mikityanska
2026-07-10 16:42:35 +03:00
committed by Paolo Abeni
parent 5329647dad
commit 842870cdfa
1 changed files with 5 additions and 5 deletions
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10
net/core/skbuff.c
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@@ -4775,6 +4775,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
struct sk_buff *tail = NULL;
struct sk_buff *list_skb = skb_shinfo(head_skb)->frag_list;
unsigned int mss = skb_shinfo(head_skb)->gso_size;
bool gso_by_frags = mss == GSO_BY_FRAGS;
unsigned int doffset = head_skb->data - skb_mac_header(head_skb);
unsigned int offset = doffset;
unsigned int tnl_hlen = skb_tnl_header_len(head_skb);
@@ -4790,7 +4791,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
int nfrags, pos;
if ((skb_shinfo(head_skb)->gso_type & SKB_GSO_DODGY) &&
mss != GSO_BY_FRAGS && mss != skb_headlen(head_skb)) {
!gso_by_frags && mss != skb_headlen(head_skb)) {
struct sk_buff *check_skb;
for (check_skb = list_skb; check_skb; check_skb = check_skb->next) {
@@ -4818,7 +4819,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
sg = !!(features & NETIF_F_SG);
csum = !!can_checksum_protocol(features, proto);
if (sg && csum && (mss != GSO_BY_FRAGS)) {
if (sg && csum && !gso_by_frags) {
if (!(features & NETIF_F_GSO_PARTIAL)) {
struct sk_buff *iter;
unsigned int frag_len;
@@ -4852,9 +4853,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
/* GSO partial only requires that we trim off any excess that
* doesn't fit into an MSS sized block, so take care of that
* now.
* Cap len to not accidentally hit GSO_BY_FRAGS.
*/
partial_segs = min(len, GSO_BY_FRAGS - 1) / mss;
partial_segs = len / mss;
if (partial_segs > 1)
mss *= partial_segs;
else
@@ -4878,7 +4878,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
int hsize;
int size;
if (unlikely(mss == GSO_BY_FRAGS)) {
if (unlikely(gso_by_frags)) {
len = list_skb->len;
} else {
len = head_skb->len - offset;