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

[Peter Maydell]

On 15 April 2013 09:54, Christoffer Dall <cdall at cs.columbia.edu> wrote:
> On Mon, Apr 15, 2013 at 1:43 AM, Marc Zyngier <marc.zyngier at arm.com> wrote:
>> As for the affinity, we can enforce this very easily.
>>
> OK, but let's not go down this road until we've verified that this is
> really an issue that needs to be handled by excluding A7s.  Andre, can
> you give us some more details?

We *must* exclude KVM vcpu threads from ever running on A7s,
because the cp15 handling code as it stands does not virtualize
various registers (most notably the ID/feature registers) and
so the vcpu will bounce between "looks like an A15" and "looks
like a weird hybrid between A7 and A15".

Assuming we don't want to tackle full big.LITTLE host support
right now, I can see two options:
 * forbid KVM completely on a system with any non-A15s
 * force KVM vcpus to only ever run on the A15s [Q: does
   all the hyp mode code have to also run on the A15s or
   is it A7-safe?]

-- PMM