Re: [Qemu-devel] qemu-kvm-0.11 regression, crashes on older guests with virtio network

[Anthony Liguori]

Mark McLoughlin wrote:
> On Thu, 2009-10-29 at 09:11 -0500, Anthony Liguori wrote:
>   
> > Mark McLoughlin wrote:
> >     
> > > >         tap_set_offload(csum: 1, tso4: 1, tso6: 1, ecn: 1)
> > > > being called and get an mtu of 1500 on virbr0 using his birdge.sh script.
> > > >
> > > > virtio_net_receive2 was trying to transfer a 1534 byte packet (1524 'size' + 10 
> > > > 'virtio_net_hdr')
> > > > and the guest only had 1524 bytes of space in its input descriptors.
> > > >     
> > > >         
> > > Okay, that sounds like a bug in Dustin's version of the guest virtio-net
> > > driver - if it is only supplying 1524 byte buffers, it should not be
> > > saying it supports the VIRTIO_NET_F_GUEST_TSO4 feature
> > >   
> > >       
> > See:
> >
> > commit 8eca6b1bc770982595db2f7207c65051572436cb
> > Author: aliguori <address@hidden>
> > Date:   Sun Apr 5 17:40:08 2009 +0000
> >
> >     Fix oops on 2.6.25 guest (Rusty Russell)
> >    
> >     I believe this is behind the following:
> >     https://bugs.edge.launchpad.net/ubuntu/jaunty/+source/linux/+bug/331128
> >    
> >     virtio_pci in 2.6.25 didn't do feature negotiation correctly: it 
> > acked every
> >     bit.  Fortunately, we can detect this.
> >    
> >     Signed-off-by: Rusty Russell <address@hidden>
> >     Signed-off-by: Anthony Liguori <address@hidden>
> >
> > It looks like Rusty's fix wasn't enough.  If I change virtio-net to only 
> > advertise F_MAC, we don't run into this problem.
> >     
>
> If it's not acking VBAD_FEATURE, then it doesn't sound like the same
> issue
>   

It was acking VBAD_FEATURE when I tested it.

But if you look at the patch, it whitelists the following features:

   features |= (1 << VIRTIO_NET_F_MAC);
   features |= (1 << VIRTIO_NET_F_GUEST_CSUM);
   features |= (1 << VIRTIO_NET_F_GUEST_TSO4);
   features |= (1 << VIRTIO_NET_F_GUEST_TSO6);
   features |= (1 << VIRTIO_NET_F_GUEST_ECN);

Which is why it's ack'ing TSO4.   Removing TSO4 didn't seem to fix it 
for me.

Regards,

Anthony Liguori