[PATCH net 0/2] udp: preserve outer transport header after tunnel GRO

[Bryon Fryer <bryon@fryer.io>]

UDP tunnel GRO can leave the inner TCP header in skb->transport_header.
The virtio tunnel exporter uses that field as the outer UDP offset,
producing descriptors which the receiving decoder rejects.

Patch 1 restores the parsed outer UDP position after successful tunnel
GRO completion. Patch 2 adds a focused regression to the existing TUN
selftest, including a GRO-off control.

This series is based on net 8d5ce4751fad. Before/after virtme-ng/KVM runs
on that base reproduced and corrected the exported offset for VXLAN,
VXLAN-GPE and Geneve, with clean GRO-off and prebuilt-GSO controls.
The complete extended TUN suite had only the added regression fail
before the fix and no unexpected failures afterward; its 12 expected
failures were unchanged. Selected UDP GSO tests passed on both variants.
Bulk TCP delivery checks also completed, with the receiving TAP rejecting
aggregates before the fix and accepting them afterward. The separate
VXLAN-GPE raw-path segmentation rejection remains outside this series.

Full x86-64 allyesconfig and allmodconfig bzImage/modules builds completed
before and after the fix with Clang/LLVM 19 and W=1. Existing baseline
warnings required KCFLAGS=-Wno-error; the fix introduced no new warnings.
The runtime kernel pair used GCC 14 with matching configurations.

The detailed timing table in patch 1 comes from three paired virtme-ng
runs. Median 32 MiB TCP transfer times fell from 69.8s to 0.15s for
VXLAN and from 70.8s to 0.16s for Geneve. Receiver rejections and
retransmissions fell to zero, all payload bytes were verified, and
GRO-off controls were clean.

Bryon Fryer (2):
  udp: restore outer transport header after tunnel GRO
  selftests: net: check UDP tunnel GRO virtio offsets

 net/ipv4/udp_offload.c            |   2 +
 tools/testing/selftests/net/tun.c | 292 ++++++++++++++++++++++++++++++
 2 files changed, 294 insertions(+)


base-commit: 8d5ce4751fad9499ea408163af7f410f18a85782
-- 
2.47.3