Re: [Qemu-devel] [Bug 1297651] [NEW] KVM create a win7 guest with Qemu, it boots up fail

[Eduardo Habkost]

On Wed, Mar 26, 2014 at 05:09:29PM +0200, Michael S. Tsirkin wrote:
> On Wed, Mar 26, 2014 at 12:06:38PM -0300, Eduardo Habkost wrote:
> > On Wed, Mar 26, 2014 at 04:54:31PM +0200, Michael S. Tsirkin wrote:
> > > On Wed, Mar 26, 2014 at 02:48:29PM +0100, Igor Mammedov wrote:
> > [...]
> > > > more clean would be to abort if CPON index (i.e. APIC ID)
> > > > is more than 255. That would affect small number of weird
> > > > topologies but sould be fine for most usecases.
> > > 
> > > Any idea how to trigger this behaviour?
> > 
> > Set sockets and/or cores to a 2^n+1 value. It will use n+1 bits for the
> > socket ID and core ID, making APIC ID larger than CPU index. You can get
> > a very large APIC ID if you use, for example:
> > 
> >   -smp 1,cores=17,threads=17,maxcpus=200
> > 
> > There's code to limit the maximum APIC ID and abort if it is too large,
> > already (so the above command-line will make QEMU abort).
> 
> Okay so how do you make this package size exactly 256?

I didn't look for a proof yet, but it looks like having apic_id_limit
exactly 256 while max_cpus <= 255 is impossible.

Laszlo, did you find a case where this was possible?

-- 
Eduardo