[libvirt] X86CPU "feature-words" property on QEMU (was Re: [PATCH v3 1/3] x86: Data structure changes to support MSR based) features
Eduardo Habkost
ehabkost at redhat.com
Fri Aug 17 18:10:57 UTC 2018
On Fri, Aug 17, 2018 at 07:59:40PM +0200, Paolo Bonzini wrote:
> On 17/08/2018 19:48, Eduardo Habkost wrote:
> > So let's do what's necessary to remove it. But I don't think the
> > removal of "feature-words" should block the inclusion of this
> > series.
> >
> > Now, should QOM properties follow our feature deprecation policy,
> > or they were never a supported external API and we can remove it
> > immediately?
> >
> > CCing Jiri and libvir-list, because I just found that there's
> > code on libvirt that uses it, but I don't know exactly it does
> > with that info.
>
> It is used to check whether the host supports invtsc and pv-unhalt and
> avoid changing the guest ABI when migrating: see
> https://marc.info/?l=libvir-list&m=152445761414746&w=2 for a patch that
> introduces one user.
>
> I think we should extend it to MSRs, not remove it.
Well, I would prefer if libvirt simply did (e.g.)
"qom-get property=invtsc" instead of fetching raw feature-words
data. But if we do have an existing user, I now agree with you:
let's keep it working and extend it to include MSR info too.
BTW, libvirt must stop using this hardcoded QOM path:
#define QOM_CPU_PATH "/machine/unattached/device[0]"
It should use the "qom_path" field of "query-cpus" instead.
--
Eduardo
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