On Wed, Nov 28, 2018 at 4:07 PM Eric Dumazet [off-list ref] wrote:

A NIC is supposed to deliver frames, even the ones that 'seem' bad.

A quick test shows this is not the case for mlx5.

With the trafgen script you gave to me, with tot_len==40, the dest host
could receive all the packets. Changing tot_len to 80, tcpdump could no
longer see any packet. (Both sender and receiver are mlx5.)

So, packets with tot_len > skb->len are clearly dropped before tcpdump
could see it, that is likely by mlx5 hardware.