[libvirt] [PATCH] i386: Re-add "pconfig" CPUID flag name
Eduardo Habkost
ehabkost at redhat.com
Fri Sep 27 11:44:51 UTC 2019
On Fri, Sep 27, 2019 at 10:09:05AM +0100, Daniel P. Berrangé wrote:
> On Thu, Sep 26, 2019 at 09:42:20PM -0300, Eduardo Habkost wrote:
> > (CCing libvir-list)
> >
> > On Thu, Sep 26, 2019 at 11:58:30PM +0200, Paolo Bonzini wrote:
> > > Is this really needed? QEMU's value of pconfig=on vs. off should be
> > > provided by QMP CPU model queries, if a property is not available then
> > > Libvirt should not try to set it to off.
> > >
> >
> > Libvirt can easily work around it for new VMs, and it should.
> >
> > The issue are VMs that were created with QEMU 3.1.0. QEMU 3.1.0
> > was telling libvirt "Icelake-Server can't be used unless
> > pconfig=off is used", and libvirt was adding pconfig=off to the
> > domain XML as expected.
> >
> > It would be wrong for libvirt to remove a device option when
> > migrating an existing VM to another QEMU version. We can change
> > the rules (and document that), but do we want to?
>
> IIUC currently any existing VMs with Icelake-Server will *not* have
> pconfig present, since libvirt is going to set pconfig=off
>
> QEMU has now dropped pconfig CPUID entirely. If libvirt were to stop
> setting pconfig=off, then there is NO guest ABI change, so we'd be
> safe in that sense.
This is correct. Only pconfig=off worked, and no accelerator
ever supported pconfig=on.
--
Eduardo
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