Re: [Qemu-devel] [RFC 7/7] target-i386: Disable direct passthrough of PMU CPUID leaf by default

[Eduardo Habkost]

On Fri, Apr 26, 2013 at 05:39:15PM +0200, Igor Mammedov wrote:
> On Fri, 26 Apr 2013 17:33:18 +0200
> Andreas Färber <address@hidden> wrote:
> 
> > Am 26.04.2013 17:31, schrieb Eduardo Habkost:
> > > On Fri, Apr 26, 2013 at 05:10:29PM +0200, Igor Mammedov wrote:
> > >> On Thu, 25 Apr 2013 15:43:06 -0300
> > >> Eduardo Habkost <address@hidden> wrote:
> > >>
> > >>> The current code handling the CPUID 0xA leaf simply forwards all data
> > >>> from GET_SUPPORTED_CPUID directly to the guest, breaking migration
> > >>> between hosts with different number of PMU counters.
> > >>>
> > >>> This patch disables this behavior, except on older machine-types (for
> > >>> compatibility) and on the "host" CPU model.
> > >> Please, make it static property and use compat properties.
> > >> Result will be simpler and  much less will have to be redone/discarded 
> > >> after
> > >> converting to the rest to properties and sub-classes.
> > > 
> > > I was going to say that static properties were too much work to be done
> > > in time for 1.5, but you are right: in this specific case adding a
> > > static property for the cpuid_pmu_passthrough field looks very easy. I
> > > will give it a try.
> > 
> > I am hoping to get as initial set (though not all) of the static
> > properties still into 1.5. Using them to fix CPUID bugs can then be done
> > during Hard Freeze. :)
> patch "[PATCH 02/10] target-i386: cpu: convert existing dynamic properties
> into static properties" should be enough for using model,level compat
> properties.

...except that we don't have X86CPU model subclasses yet, so we can't
set model-specific compat properties using compat_props.

Maybe we can make compat_props work for pmu-passthrough, but it may be
not completely straightforward because I would like to keep it enabled
by default on -cpu host.

-- 
Eduardo