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

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Date:	Wed, 18 Dec 2013 18:05:18 -0800
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Wei-Chun Chao <weichunc@...mgrid.com>
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, 18 Dec 2013 17:51:25 -0800
Wei-Chun Chao <weichunc@...mgrid.com> wrote:

> 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

I was hoping more that generic tunnel code could just do software UFO/GSO
for now, and when somebody has hardware that handles nested GSO they could
provide a feature flag mechanism.
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