[PATCH] ARM: KVM: iterate over all CPUs for CPU compatibility check

[Russell King - ARM Linux]

On Fri, Apr 12, 2013 at 02:49:43PM +0100, Marc Zyngier wrote:
> On 12/04/13 14:40, Peter Maydell wrote:
> > On 12 April 2013 14:24, Marc Zyngier <marc.zyngier at arm.com> wrote:
> >> Nak. The fact that one of the CPUs seem to hang is a sure sign that
> >> something is severely broken, and you definitely want to fix that issue,
> >> instead of blindly ignoring it.
> >>
> >> Additionally, it seems you're just papering over the issue. You should
> >> be able to exclude the A7 processors, but not completely deny KVM from
> >> running on the hardware.
> > 
> > Well that might be nice, as would fully supporting big.LITTLE
> > systems. But until somebody actually does that work it seems
> > like a better idea to fail gracefully rather than having a 50%
> > chance of failing gracefully and a 50% chance of going weird.
> 
> Nothing prevents the kernel (or even the user) from forcing the affinity
> of the CPU threads to the A15s. I'm not saying we should ignore the
> problem either. Just that the proposed approach is wrong.

But nothing guarantees that you get that affinity.  If you offline all
A15 CPUs, then you will find those threads running on whatever is left.
Affinity is just a hint, nothing more.