Re: [RFC] cpu_map: Remove pconfig from Icelake-Server CPU model

[Huang, Kai]

On Mon, 2019-09-30 at 17:16 +0200, Paolo Bonzini wrote:
> On 30/09/19 16:31, Hu, Robert wrote:
> > > This might be a problem if there are plans to eventually make KVM support
> > > pconfig, though.  Paolo, Robert, are there plans to support pconfig in KVM
> > > in the
> > > future?
> > [Robert Hoo] 
> > Thanks Eduardo for efforts in resolving this issue, introduced from my
> > Icelake CPU
> > model patch.
> > I've no idea about PCONFIG's detail and plan. Let me sync with Huang, Kai
> > and answer
> > you soon.
> 
> It's really, really unlikely.  It's possible that some future processor
> overloads PCONFIG in such a way that it will become virtualizable, but
> not IceLake.

I agree. Not Icelake.

Thanks,
-Kai

> 
> Would it make sense for libvirt to treat absent CPU flags as "default
> off" during migration, so that it can leave out the flag in the command
> line if it's off?  If it's on, libvirt would pass pconfig=on as usual.
> This is a variant of [2], but more generally applicable:
> 
> > [2] However starting a domain with Icelake-Server so that it can be
> > migrated or saved/restored on QEMU in 3.1.1 and 4.0.0 would be
> > impossible. This can be solved by a different hack, which would drop
> > pconfig=off from QEMU command line.
> 
> Paolo