Re: [PATCH v3 net] bnxt_en: fix DMA mapping length for padded small packets

[Joe Damato <joe@dama.to>]

On Wed, Oct 07, 2026 at 03:58:31PM -0700, Michael Chan wrote:
> On Tue, Oct 6, 2026 at 10:17 PM Eric Dumazet <edumazet@kernel.org> wrote:
> 
> > Fix this by using skb_put_padto(skb, BNXT_MIN_PKT_SIZE) in
> > bnxt_start_xmit(), before skb_shinfo(skb)->nr_frags is sampled,
> > because padding might linearize the skb.
> > This ensures skb->len and skb_headlen(skb) reflect the padded size so
> > that dma_map_single() maps the full buffer and the descriptor length is
> > consistent. This also removes the temporary 'pad' variable and masking logic.
> >
> > The padding is done after the SW USO branch, otherwise
> > bnxt_sw_udp_gso_xmit() would account the padding as UDP payload
> > and send it in extra segments.
> >
> > Note that SW USO segments are still not padded: with IPv4, a segment
> > carrying less than 10 bytes of UDP payload (small gso_size, or a short
> > last segment) is sent as a frame shorter than BNXT_MIN_PKT_SIZE.
> > This is a separate issue, left for a followup patch.
> >
> > Fixes: c0c050c58d84 ("bnxt_en: New Broadcom ethernet driver.")
> > Cc: stable@vger.kernel.org
> > Reported-by: Stefan Fleischmann <sfle@kth.se>
> > Closes: https://lore.kernel.org/netdev/20261004122616.56714cbd@nargothrond/
> > Assisted-by: LLM
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> 
> v3 looks perfect to me for non SW USO packets.  Thanks.

FWIW: Once Eric's patch is in, I'll try to come up with a SW USO fix.
Thanks Eric for facing off with sashiko.