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

[Anthony Liguori <anthony@codemonkey.ws>]

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 <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>
>> 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 <rusty@rustcorp.com.au>
>>     Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
>>
>> 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