Re: [Qemu-devel] [PATCHv3] qemu: enable PV EOI for qemu 1.3

[Eduardo Habkost]

On Mon, Oct 22, 2012 at 03:12:00PM +0200, Michael S. Tsirkin wrote:
> On Mon, Oct 22, 2012 at 12:06:42PM +0200, Andreas Färber wrote:
> > Am 18.10.2012 17:01, schrieb Michael S. Tsirkin:
> > > Enable KVM PV EOI by default. You can still disable it with
> > > -kvm_pv_eoi cpu flag. To avoid breaking cross-version migration,
> > > enable only for qemu 1.3 (or in the future, newer) machine type.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <address@hidden>
> > 
> > Thanks for updating,
> > 
> > Reviewed-by: Andreas Färber <address@hidden>
> > 
> > The commit message is not so telling whether there are any downsides
> > (security implications?) to enabling this by default if supported,
> 
> I don't think there could be security downsides because all this does
> is tell guest about the feature in a convenient way.
> A well behaved guest doesn't use a feature unless it's listed but
> that's irrelevant for security.

True. It could be relevant if the host kernel did check the CPUID bits
before letting the guest read or write the PV EOI MSR, but that's not
the case.

> 
> > so
> > I'll leave it to Anthony to ack/apply this.
> > 
> > Regards,
> > Andreas
> 
> It used to be enabled. It was turned off in
> ef8621b1a3b199c348606c0a11a77d8e8bf135f1
> because it affected migration format and doing that
> just before the release seemed too risky.
> 
> 
> > -- 
> > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
> > GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg

-- 
Eduardo