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

[Stefan Fleischmann <sfle@kth.se>]

On Sun, 4 Oct 2026 21:14:31 -0700
Michael Chan <michael.chan@broadcom.com> wrote:

> On Sun, Oct 4, 2026 at 7:38 PM Eric Dumazet <edumazet@kernel.org>
> wrote:
> 
> > This issue was exposed after commit 447cbe95ebb9 ("vlan: fix
> > skb_under_panic and races when toggling HW VLAN offload") because
> > reserving extra VLAN headroom rounded LL_RESERVED_SPACE from 48 up
> > to 64 bytes, shifting skb->data offsets and potentially causing
> > small frames to land right against page boundaries.
> >
> > Fix this by using skb_put_padto(skb, BNXT_MIN_PKT_SIZE) in the
> > normal_tx path. 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.
> >
> > 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/
> > Signed-off-by: Eric Dumazet <edumazet@google.com>  
> 
> Thanks.
> Reviewed-by: Michael Chan <michael.chan@broadcom.com>

Thanks a lot! I am testing the patch right now on 6.18.55. The system
is already up for two hours without issues. Before the patch I couldn't
get past 45 minutes without hitting the IOMMU DMA read fault.

Best,
Stefan