netdev - Re: [PATCH] udp:nat:vxlan tx after nat should recsum if vxlan tx offload on

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Message-ID: <fae01ad9-4270-2153-9ba4-cf116c8ed975@gmail.com>
Date:   Mon, 3 Apr 2023 11:56:22 +0100
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Fei Cheng <chenwei.0515@...edance.com>
Cc:     dsahern@...nel.org, davem@...emloft.net,
        netfilter-devel@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>, ecree@....com
Subject: Re: [PATCH] udp:nat:vxlan tx after nat should recsum if vxlan tx
 offload on

On 02/04/2023 19:18, Willem de Bruijn wrote:
> On Fri, Mar 31, 2023 at 10:31 PM Fei Cheng <chenwei.0515@...edance.com> wrote:
>>
>> From: "chenwei.0515" <chenwei.0515@...edance.com>
>>
>>     If vxlan-dev enable tx csum offload, there are two case of CHECKSUM_PARTIAL,
>>     but udp->check donot have the both meanings.
>>
>>     1. vxlan-dev disable tx csum offload, udp->check is just pseudo hdr.
>>     2. vxlan-dev enable tx csum offload, udp->check is pseudo hdr and
>>        csum from outter l4 to innner l4.
>>
>>     Unfortunately if there is a nat process after vxlan tx，udp_manip_pkt just use
>>     CSUM_PARTIAL to re csum PKT, which is just right on vxlan tx csum disable offload.

In case 1 csum_start should point to the (outer) UDP header, whereas in
 case 2 csum_start should point to the inner L4 header (because in the
 normal TX path w/o NAT, nothing else will ever need to touch the outer
 csum after this point).

> The issue is that for encapsulated traffic with local checksum offload,
> netfilter incorrectly recomputes the outer UDP checksum as if it is an
> unencapsulated CHECKSUM_PARTIAL packet, correct?

So if netfilter sees a packet with CHECKSUM_PARTIAL whose csum_start
 doesn't point to the header nf NAT is editing, that's exactly the case
 where it needs to use lco_csum to calculate the new outer sum.  No?

-ed

PS. Fei, your emails aren't reaching the netdev mailing list, probably
 because you're sending as HTML.  Please switch to plain text.