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

[Christoffer Dall]

On Mon, Apr 15, 2013 at 5:26 PM, Geoff Levand <geoff at infradead.org> wrote:
> On Sun, 2013-04-14 at 21:57 -0700, Christoffer Dall wrote:
>> On Fri, Apr 12, 2013 at 6:24 AM, 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.
>> >
>> Marc, I disagree with this nak. If the current kernel breaks boot on a
>> Big.Little system, we need to take care of that first, and the
>> proposed patch is a quick way to do so, and it does not stand in the
>> way of introducing proper Big.Little support in any way, which I'm
>> sure is going to open up a lot of other interesting questions.
>>
>> I'm going to take this one.
>
> Since this problem will cause the 3.9 kernel to hang then a workaround
> like this should go in.  There isn't enough time to do a proper fix for
> 3.9, and even if it could be done I think it would be too intrusive to
> get merged this late.
>
That's why I was inclined to take the patch, but as Marc pointed out
the error message is incorrect, so that should be fixed at the very
least. Also I don't think we need the counting logic, just bail out if
we have any CPUs that are not supported.

Marc, since you're the strongest opponent of this patch, are you still
opposed to making sure we don't try to run KVM on Big.Little until
support is properly introduced?

I also cannot see how we can fix the affinity issue easily from within
the kernel, do you have a concrete approach in mind you can share?

Note that this is irrespective of the boot delay issue that you guys
are observing.

-Christoffer