From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: [Qemu-devel] qemu-kvm-0.11 regression, crashes on older guests
 with virtio network
Date: Thu, 29 Oct 2009 09:11:37 -0500
Message-ID: <4AE9A299.5060003@codemonkey.ws>
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Cc: Scott Tsai <scottt.tw@gmail.com>,
	Dustin Kirkland <kirkland@canonical.com>,
	qemu-devel <qemu-devel@nongnu.org>, kvm <kvm@vger.kernel.org>
To: Mark McLoughlin <markmc@redhat.com>
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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.

Regards,

Anthony Liguori