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From: Mark McLoughlin <markmc@redhat.com>
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Date: Wed, 14 Jan 2009 09:22:58 +0000
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Subject: [Qemu-devel] Re: virtio breakage with 2.6.25 guest kernel
Reply-To: Mark McLoughlin <markmc@redhat.com>, qemu-devel@nongnu.org
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To: Alexander Graf <agraf@suse.de>
Cc: "rusty@rustcorp.com.au" <rusty@rustcorp.com.au>, kvm-devel <kvm@vger.kernel.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

On Tue, 2009-01-13 at 22:05 +0100, Alexander Graf wrote:

> On 13.01.2009, at 21:14, Anthony Liguori <anthony@codemonkey.ws> wrote:
> 
> > Alexander Graf wrote:
> >> Hi,
> >>
> >> while I don't fully understand the problem, here's what I  
> >> experience so far:
> >>
> >> When using an openSUSE 11.0 kernel (2.6.25) in the guest, virtio on  
> >> tap
> >> breaks with current KVM git, while it used to work before (haven't
> >> bisected, definitely worked in kvm-78, but is probably due to  
> >> Anthony's
> >> rewrite). It shows the following message (comes from qemu):
> >>
> >
> > There were a couple of old-guest-breaking regressions.  I think  
> > we've fixed all of them but there could be more.  Are you using the  
> > latest kvm-userspace?

See:

  http://lists.gnu.org/archive/html/qemu-devel/2009-01/msg00574.html

> This one is definitely due to the broken guest kernel. I applied the  
> patch mark mentioned to ours and things started working.
> 
> So the only way I can think of to 'fix' it is by detecting broken  
> guests. We could supply a host mask of 0xffffffff and see if tge guest  
> feature mask is tge same. If so, feature masking is probably broken.

Nice idea, but no way of making the guest through feature detection
negotiation, I don't think.

Cheers,
Mark.