On 11/27/2018 03:21 PM, Cong Wang wrote:
> When an ethernet frame is padded to meet the minimum ethernet frame
> size, the padding octets are not covered by the hardware checksum.
> Fortunately the padding octets are ususally zero's, which don't affect
> checksum. However, we have a switch which pads non-zero octets, this
> causes kernel hardware checksum fault repeatedly.
>
> Prior to commit 88078d98d1bb ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE
> are friends"),
> skb checksum is forced to be CHECKSUM_NONE when padding is detected.
> After it, we have to keep skb->csum updated, like what we do for FCS.
>
> The logic is a bit complicated when dealing with both FCS and padding,
> so I wrap it up in a helper function mlx5e_csum_padding().
>
> I tested this patch with RXFCS on and off, it works fine without any
> warning in both cases.
>
> Fixes: 88078d98d1bb ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are
> friends"),
> Cc: Saeed Mahameed <sae...@mellanox.com>
> Cc: Eric Dumazet <eduma...@google.com>
> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
> ---
> .../net/ethernet/mellanox/mlx5/core/en_rx.c | 36 +++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> index 16985ca3248d..93c18647ca74 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> @@ -732,6 +732,35 @@ static u8 get_ip_proto(struct sk_buff *skb, __be16 proto)
> ((struct ipv6hdr *)ip_p)->nexthdr;
> }
>
> +static void mlx5e_csum_padding(struct sk_buff *skb, int network_depth,
> + __be16 proto, bool has_fcs)
> +{
> + u32 frame_len = has_fcs ? skb->len - ETH_FCS_LEN : skb->len;
> + void *ip_p = skb->data + network_depth;
> + u32 pad_offset, pad_len;
> + void *pad;
> +
> + if (likely(frame_len > ETH_ZLEN))
> + return;
> +
But the padding might be added on normal packets (say 1000 bytes + 3 bytes of
padding) ?
The bug here is that mlx5 csum only includes the data in IP frame.
I would simply force skb->ip_summed to CHECKSUM_NONE if any padding is detected.
Otherwise, your patch needs more work when multiple frags are used (ie
num_frags > 1 )
