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

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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@xxxxxxxxxxxxxxx>
   Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>

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
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