On Wednesday 14 January 2009 19:52:58 Mark McLoughlin wrote:

> 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.

Just add a feature "VIRTIO_F_LIES_ABOUT_FEATURES"? No guest should ever set this.

But I'm not sure it's worth the pain...

Rusty.