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Date: Fri, 11 Nov 2016 09:44:03 -0500
From: Kevin O'Connor <kevin@koconnor.net>
Message-ID: <20161111144403.GA15857@morn.lan>
References: <20161111135717.18eaa6dc@nial.brq.redhat.com>
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In-Reply-To: <20161111153619.3ef19ccb@nial.brq.redhat.com>
Subject: Re: [Qemu-devel] FW_CFG_NB_CPUS vs fwcfg file 'etc/boot-cpus'
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To: Igor Mammedov <imammedo@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>, qemu-devel@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>, mst@redhat.com, Stefan Hajnoczi <stefanha@gmail.com>, Gerd Hoffmann <kraxel@redhat.com>, "Jordan Justen (Intel address)" <jordan.l.justen@intel.com>, Jeff Fan <jeff.fan@intel.com>

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.

-Kevin