Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 10, 2019 at 06:23:00PM +0200, Laszlo Ersek wrote:
> On 10/10/19 14:48, Igor Mammedov wrote:
> 
> > it doesn't really matter if it's ACPI blob or fw_cfg,
> > what firmware needs is a table of possible CPUs with APIC IDs.
> 
> To repeat my previous point:
> 
> Not necessarily taking sides between "data table" and "register block",
> but *if* we opt for "data table", then it *must* be fw_cfg.
> 
> > But if we go this route (i.e. not reuse CPU hotplug interface),
> > the table alone is not enough, one would need to build a protocol
> > between ACPI and firmware to communicate what CPUs to (un)hotplug.
> 
> That's for sure, yes -- for finding out what CPU has been hotplugged,
> the hotplug SMI handler in the firmware has to look at the register
> block no matter what.

I thought all that's done by ACPI, with ACPI returning an event
to the OSPM reporting what happened.

> The "data table" vs "register block" question only arises *afterwards*,
> for translating the CPU selector (fetched from the register block) to
> the APIC-ID domain. (The generic edk2 infrastructure requires APIC-IDs).
> 
> Thanks
> Laszlo