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Date:   Mon, 11 Feb 2019 09:24:01 -0800
From:   Eric Dumazet <>
To:     Tariq Toukan <>,
        "David S. Miller" <>
Cc:, Eran Ben Elisha <>,
        Saeed Mahameed <>,
        Eric Dumazet <>
Subject: Re: [PATCH net V2] net/mlx4_en: Force CHECKSUM_NONE for short
 ethernet frames

On 02/11/2019 08:04 AM, Tariq Toukan wrote:
> From: Saeed Mahameed <>
> 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 usually zero's, which don't affect
> checksum. However, it is not guaranteed. For example, switches might
> choose to make other use of these octets.
> This repeatedly causes kernel hardware checksum fault.
> Prior to the cited commit below, skb checksum was forced to be
> CHECKSUM_NONE when padding is detected. After it, we need to keep
> skb->csum updated. However, fixing up CHECKSUM_COMPLETE requires to
> verify and parse IP headers, it does not worth the effort as the packets
> are so small that CHECKSUM_COMPLETE has no significant advantage.
> Future work: when reporting checksum complete is not an option for
> IP non-TCP/UDP packets, we can actually fallback to report checksum
> unnecessary, by looking at cqe IPOK bit.
> Fixes: 88078d98d1bb ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends")
> Cc: Eric Dumazet <>
> Signed-off-by: Saeed Mahameed <>
> Signed-off-by: Tariq Toukan <>

Thanks Tariq and Saeed

Reviewed-by: Eric Dumazet <>

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