On Wed, Jul 30, 2025 at 4:06 AM Gal Pressman [off-list ref] wrote:

On 29/07/2025 21:34, Christoph Paasch via B4 Relay wrote:

quoted

From: Christoph Paasch <redacted>

When gso_segs is left at 0, a number of assumptions will end up being
incorrect throughout the stack.

For example, in the GRO-path, we set NAPI_GRO_CB()->count to gso_segs.
So, if a non-LRO'ed packet followed by an LRO'ed packet is being
processed in GRO, the first one will have NAPI_GRO_CB()->count set to 1 and
the next one to 0 (in dev_gro_receive()).
Since commit 531d0d32de3e
("net/mlx5: Correctly set gso_size when LRO is used")
these packets will get merged (as their gso_size now matches).
So, we end up in gro_complete() with NAPI_GRO_CB()->count == 1 and thus
don't call inet_gro_complete(). Meaning, checksum-validation in
tcp_checksum_complete() will fail with a "hw csum failure".

Even before the above mentioned commit, incorrect gso_segs means that other
things like TCP's accounting of incoming packets (tp->segs_in,
data_segs_in, rcv_ooopack) will be incorrect. Which means that if one
does bytes_received/data_segs_in, the result will be bigger than the
MTU.

Fix this by initializing gso_segs correctly when LRO is used.

Fixes: e586b3b0baee ("net/mlx5: Ethernet Datapath files")

Maybe we should put an additional Fixes line for the gso_size patch?
It doesn't directly fix it, but it will clearly emphasize the importance
of picking up this patch together with the other one.

quoted

Reported-by: Gal Pressman <redacted>
Closes: https://lore.kernel.org/netdev/6583783f-f0fb-4fb1-a415-feec8155bc69@nvidia.com/ (local)
Signed-off-by: Christoph Paasch <redacted>

Thanks Christoph,
Reviewed-by: Gal Pressman <redacted>

I do not think we need many Fixes: tag.

Reviewed-by: Eric Dumazet <edumazet@google.com>

If we really want to be precise, the issue also came when GRO got
support for GRO packets ;)

commit 5eddb24901ee    gro: add support of (hw)gro packets to gro stack

This commit really implied that both gso_size and gso_segs had to be
set by drivers RX paths.

It seems drivers/net/ethernet/google/gve/gve_rx_dqo.c has a similar issue.

gve_rx_complete_rsc() sets gso_size but not gso_segs

shinfo->gso_size = le16_to_cpu(desc->rsc_seg_len);