Re: [PATCH] SVM: forbid guest to execute monitor/mwait

Joerg Roedel
2007-03-22T09:56:05Z

On Thu, Mar 22, 2007 at 09:38:12AM +0200, Avi Kivity wrote:
> Joerg Roedel wrote:
> >From: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>
> >
> >This patch forbids the guest to execute monitor/mwait instructions on
> >SVM. This is necessary because the guest can execute these instructions
> >if they are available even if the kvm cpuid doesn't report its
> >existence.
> >
> >
>
> You're intercepting the instructions unconditionally. What about the case where cpuid does
> report monitor/mwait support? The guest can legitimately use them then.

I prepared a patch for QEmu to handle this but finally not
submitted it because QEmu does not set the Monitor bit anyway. But you
are right. It is possible for userspace to set the Montior bit and the
guest won't be able to use it.
I think an architecture dependent cpuid mask feature in the kernel would
solve this problem. I'll prepare a patch for that.

Joerg