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[Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost
From: |
Cornelia Huck |
Subject: |
[Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost |
Date: |
Tue, 1 Dec 2015 11:11:08 +0100 |
Some of our test folks tried to run a recent-ish qemu (nearly 2.5)
combined with an old host kernel (and a virtio-1 capable guest).
In that setup, we had the transport (in that case, virtio-ccw)
advertise VERSION_1 as it is a revision 1 device. However, the old
vhost driver did not support virtio-1 and therefore cleared the
VERSION_1 bit. In the end, qemu did not offer VERSION_1 to the guest
for a revision 1 device, which the guest treats as a fatal error.
It looks to me as if virtio-pci has the same problem: The kernel will
detect a modern device as by the I/O layout and then barf at the
missing VERSION_1 feature bit.
We _could_ make this missing VERSION_1 bit non-fatal in the guest, but
that does not fix guests that are already out there.
The problem is that the transport cannot know whether the VERSION_1 bit
will be pulled from under it later during device setup: This is only
done in the ->get_features() callback when virtio-net will handle the
features supported by vhost.
I'm currently lacking a good idea on how to fix this, but I think that
is an issue that should be dealt with for 2.5...
- [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost,
Cornelia Huck <=
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Cornelia Huck, 2015/12/01
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Cornelia Huck, 2015/12/01
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Jason Wang, 2015/12/02
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Cornelia Huck, 2015/12/02
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Michael S. Tsirkin, 2015/12/02
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Jason Wang, 2015/12/03
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Cornelia Huck, 2015/12/04
- Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost, Michael S. Tsirkin, 2015/12/04