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Date: Fri, 11 Nov 2016 16:05:59 +0100
From: Igor Mammedov <imammedo@redhat.com>
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Subject: Re: [Qemu-devel] FW_CFG_NB_CPUS vs fwcfg file 'etc/boot-cpus'
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To: Kevin O'Connor <kevin@koconnor.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>, mst@redhat.com, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>, "Jordan Justen (Intel address)" <jordan.l.justen@intel.com>, Laszlo Ersek <lersek@redhat.com>, Jeff Fan <jeff.fan@intel.com>

On Fri, 11 Nov 2016 09:44:03 -0500
"Kevin O'Connor" <kevin@koconnor.net> wrote:

> On Fri, Nov 11, 2016 at 03:36:19PM +0100, Igor Mammedov wrote:
> > On Fri, 11 Nov 2016 15:02:36 +0100
> > Laszlo Ersek <lersek@redhat.com> wrote:
> >   
> > > adding Jeff Fan and Jordan Justen
> > > 
> > > On 11/11/16 13:57, Igor Mammedov wrote:  
> > > > While looking at OVMF and how it handles CPUs (ACPI/AP wakeup),
> > > > I've noticed that it uses legacy FW_CFG_NB_CPUS(0x05) to get
> > > > the number of present at start CPUs.    
> > > 
> > > Where exactly do you see this?  
> > That's the only place in OVMF, but according to google there are
> > other firmwares that use FW_CFG_NB_CPUS so we are not free to remove
> > it and break guests.
> > 
> > So I'd just drop not yet released 'etc/boot-cpus',
> > of cause SeaBIOS should be fixed and its blob in QEMU updated.  
> 
> I have no preference between FW_CFG_NB_CPUS and 'etc/boot-cpus'.  Note
> that SeaBIOS v1.10 was released with the code using 'etc/boot-cpus'
> though.  If it's to go away, we'll need a SeaBIOS stable branch
> release with the change.
Yep, we'd need a stable for that.
It still probably better then keeping 2 exactly same interfaces
when we have a chance to maintain only one.

Without supplier of 'etc/boot-cpus' (QEMU) it will behave like
it used before, i.e. hang with x2apic configuration.

> 
> -Kevin
>