On Tue, Nov 27, 2018 at 5:25 PM Eric Dumazet [off-list ref] wrote:

On 11/27/2018 04:07 PM, Cong Wang wrote:

quoted

On Tue, Nov 27, 2018 at 3:48 PM Eric Dumazet [off-list ref] wrote:

quoted

quoted

But the padding might be added on normal packets (say 1000 bytes + 3 bytes of padding) ?

I never see other padding cases than ETH_ZLEN. Does ethernet standard
require padding for other cases? I only read the section "3.2.8 Pad field" in
the standard.

Padding can be done by senders, eg using AF_PACKET,
added at the tail of a regular IP/IP6 frame of 1000 or 6000 bytes.

I tried the trafgen script you provided, it doesn't trigger any checksum fault.
So, it is probably a different case.

Note that mlx5 will presumably set CHECKSUM_UNNECESSARY for standard protocols,
so if you want to reproduce the issue, you might need to find an IP frame that
mlx5 is not able to checksum validate.

This warning is 100% reproducible with a TCP RST packet (no data)
here, after I find the right switch which pads non-zero's. This is
also how I verified this patch.

Thanks.