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

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 26 Apr 2013 14:30:40 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Fri, Apr 26, 2013 at 05:39:15PM +0200, Igor Mammedov wrote:
> > On Fri, 26 Apr 2013 17:33:18 +0200
> > Andreas Färber <afaerber@suse.de> 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 <ehabkost@redhat.com> 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.
X86CPU could serve here

> 
> 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.
Maybe for 'host' hack realize() to override default, will do and later we
can move it to host_subclass.

it's easier to re-factor than compact functions
> 
> -- 
> Eduardo
> 


-- 
Regards,
  Igor