[libvirt] [Qemu-devel] [RFC 0/5] Allow object-add on X86CPU subclasses, for CPU model probing

[Eduardo Habkost]

On Thu, May 15, 2014 at 02:35:01PM +0200, Igor Mammedov wrote:
> On Tue, 06 May 2014 22:29:24 +0200
> Andreas Färber <afaerber at suse.de> wrote:
> 
> > Am 06.05.2014 22:19, schrieb Eduardo Habkost:
> > > On Tue, May 06, 2014 at 10:01:11PM +0200, Igor Mammedov wrote:
> > >> On Tue, 6 May 2014 11:42:56 -0300
> > >> Eduardo Habkost <ehabkost at redhat.com> wrote:
> > >>> On Tue, May 06, 2014 at 09:22:38AM +0200, Igor Mammedov wrote:
> > >>>> On Fri, 2 May 2014 11:43:05 -0300
> > >>>> Eduardo Habkost <ehabkost at redhat.com> wrote:
> > >>>>> On Fri, May 02, 2014 at 03:45:03PM +0200, Igor Mammedov wrote:
> > >>>>>> On Wed, 30 Apr 2014 17:29:28 -0300
> > >>>>>> Eduardo Habkost <ehabkost at redhat.com> wrote:
> > >>>>>>> This series allows management code to use object-add on X86CPU subclasses, so it
> > >>>>>> Is there any reason why "device-add" couldn't be used?
> > >>>>> It needs to work with "-machine none", device_add requires a bus to
> > >>>>> exist, and there is no icc-bus on machine_none.
> > >>>> The thing is that CPUID is a function of machine so using
> > >>>> "-machine none" will provide only approximately accurate data.
> > >>>> I'm not sure that retrieved possibly not accurate data are useful
> > >>>> for libvirt.
> > >>> "-cpu host" doesn't depend on machine, and is the most important thing
> > >>> right now (because libvirt's checks for host QEMU/kernel/CPU
> > >>> capabilities is completely broken).
> > >> true, but device-add/-cpu host could be used right now to get the
> > >> same CPUID data wile using any machine type or default one without
> > >> any of this patches.
> > > 
> > > device_add can't be used with "-machine none".
> > 
> > I see no reason why we couldn't *make* CPUs work on -machine none. The
> > ICC bus and bridge were a hack to make APIC(?) hot-add work in face of
> > SysBus; if that prohibits other valid uses now, then evaluating Igor's
> > memory work for CPU might be an option.
> Yep, if CPU is hot-plugged as bus-less device.
> There is a little concern of APIC device if we go that direction since
> in addition to hotpluggable BUS, BUS provides address-space for APIC MMIO.
> With that resolved, x86-cpu shouldn't depend on any bus and if there isn't
> any current user that uses QOM path to CPU for introspecting (Eduardo's
> ABI concern), then it could be done in time for 2.1.

Maybe there are no users of the current QOM path, but we do need a
stable path to allow management to locate the CPU objects. Do we have
one, already?

-- 
Eduardo