netdev - Re: [PATCH net-next] ipv4: fix tunneled VM traffic over hw VXLAN/GRE GSO NIC

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Message-ID: <CACviX4H9L7TFXCvhaxUxkpMR+jPU02BrQAby2BbS+b0earxDbQ@mail.gmail.com>
Date:	Wed, 18 Dec 2013 17:51:25 -0800
From:	Wei-Chun Chao <weichunc@...mgrid.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	davem <davem@...emloft.net>,
	"eric.dumazet" <eric.dumazet@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	netdev <netdev@...r.kernel.org>,
	"joseph.gasparakis" <joseph.gasparakis@...el.com>,
	Or Gerlitz <or.gerlitz@...il.com>
Subject: Re: [PATCH net-next] ipv4: fix tunneled VM traffic over hw VXLAN/GRE
 GSO NIC

On Wed, Dec 18, 2013 at 4:35 PM, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> On Wed, 18 Dec 2013 11:02:48 -0800
> Wei-Chun Chao <weichunc@...mgrid.com> wrote:
>
>> This is also seen on 'net'.
>>
>> VM to VM GSO traffic is broken if it goes through VXLAN or GRE
>> tunnel and the physical NIC on the host supports hardware VXLAN/GRE
>> GSO offload (e.g. bnx2x and next-gen mlx4).
>>
>> Two issues -
>> (VXLAN) VM traffic has SKB_GSO_DODGY and SKB_GSO_UDP_TUNNEL with
>> SKB_GSO_TCP/UDP set depending on the inner protocol. GSO header
>> integrity check fails in udp4_ufo_fragment if inner protocol is
>> TCP. Also gso_segs is calculated incorrectly using skb->len that
>> includes tunnel header. Fix: robust check should only be applied
>> to the inner packet.
>>
>> (VXLAN & GRE) Once GSO header integrity check passes, NULL segs
>> is returned and the original skb is sent to hardware. However the
>> tunnel header is already pulled. Fix: tunnel header needs to be
>> restored so that hardware can perform GSO properly on the original
>> packet.
>>
>> Signed-off-by: Wei-Chun Chao <weichunc@...mgrid.com>
>> ---
>
> Is there someway the tunnel could fixup the GSO bits?

Thanks, Stephen.

You meant handling DODGY bit (and unsetting it) before GRE and VXLAN
encap? I guess we can do

    if (skb_shinfo(skb)->gso_type & SKB_GSO_DODGY) {
        skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss);
        skb_shinfo(skb)->gso_type &= ~(SKB_GSO_DODGY);
    }


in handle_offloads(vxlan.c) and gre_handle_offloads(gre.h). We will
save the overhead to pull and push the tunnel header later. Though
since skb->dev is not known at this time yet, this will be done
unconditionally unlike before (done only when skb_gso_ok return true).

Weichun
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