netdev - Re: [PATCH net v2] net/mlx4_en: don't set CHECKSUM

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Date:   Tue, 8 Aug 2017 19:14:38 +0300
From:   Saeed Mahameed <saeedm@....mellanox.co.il>
To:     Davide Caratti <dcaratti@...hat.com>
Cc:     Tariq Toukan <tariqt@...lanox.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net v2] net/mlx4_en: don't set CHECKSUM_COMPLETE on SCTP packets

On Tue, Aug 8, 2017 at 7:06 PM, Davide Caratti <dcaratti@...hat.com> wrote:
> On Tue, 2017-08-08 at 18:07 +0300, Saeed Mahameed wrote:
>> >   {
>> >          __u16 length_for_csum = 0;
>> >          __wsum csum_pseudo_header = 0;
>> > +       __u8 ipproto = iph->protocol;
>> > +
>> > +       if (unlikely(ipproto == IPPROTO_SCTP))
>> > +               return -1;
>> >
>>
>> Hi Davide
>>
>
> hi Saeed,
>
> thank you for looking at this!
>
>> If you got to here then it means this is a non UDP/TCP ipv4 packet and
>> the HW failed to validate it's checksum but
>> you get from the connectx3 HW a 1's complement 16-bit sum of IP
>> Payload + IP pseudo-header.
>> so if you return -1 here the driver will report checksum none for this
>> packet (and you will abandon any checsum offload/help from HW).
>>
>> I am not an SCTP expert but it seems that you decided here that
>> connectX3 hw checksum (described above) can't be used to calculate
>> SCTP packet checksum
>> is that correct?
>>
> Yes, that's correct. SCTP uses CRC32c, not 1's complement (and does not use
> pseudo-headers): therefore, the checksum computed by the NIC hardware can't
> be used.
>
> The issue I observed is skb->ip_summed set to CHECKSUM_COMPLETE, that made
> CRC32c validation fail in my setup (that was a netfilter REJECT rule, matching
> SCTP packets). AFAIK, CHECKSUM_COMPLETE is valid only for the Internet Checksum;
> setting CHECKSUM_NONE on rx packets carrying IPPROTO_SCTP fixed my test scenario.
>
>> If so, then i am ok with this patch.
>
> I planned to post this some weeks ago, after agreeing v2 with Tariq
> (https://www.spinics.net/lists/netdev/msg441231.html), but took some time to
> find a ConnectX-3 (from what I saw the issue is not present on ConnectX-3 Pro,
> since it has MLX4_RX_CSUM_MODE_VAL_NON_TCP_UDP bit set to 0).
>

Thanks for the clarification, I will ack the patch.

> regards,
> --
> davide
>