Re: [PATCH net] net/mlx5e: fix csum adjustments caused by RXFCS

[David Miller <davem@davemloft.net>]

From: Eric Dumazet <edumazet@google.com>
Date: Tue, 30 Oct 2018 00:57:25 -0700

> As shown by Dmitris, we need to use csum_block_add() instead of csum_add()
> when adding the FCS contribution to skb csum.
> 
> Before 4.18 (more exactly commit 88078d98d1bb "net: pskb_trim_rcsum()
> and CHECKSUM_COMPLETE are friends"), the whole skb csum was thrown away,
> so RXFCS changes were ignored.
> 
> Then before commit d55bef5059dd ("net: fix pskb_trim_rcsum_slow() with
> odd trim offset") both mlx5 and pskb_trim_rcsum_slow() bugs were canceling
> each other.
> 
> Now we fixed pskb_trim_rcsum_slow() we need to fix mlx5.
> 
> Note that this patch also rewrites mlx5e_get_fcs() to :
> 
> - Use skb_header_pointer() instead of reinventing it.
> - Use __get_unaligned_cpu32() to avoid possible non aligned accesses
>   as Dmitris pointed out.
> 
> Fixes: 902a545904c7 ("net/mlx5e: When RXFCS is set, add FCS data into checksum calculation")
> Reported-by: Paweł Staszewski <pstaszewski@itcare.pl>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied and queued up for -stable.