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

[Christoffer Dall]

On Mon, Apr 15, 2013 at 6:48 AM, Will Deacon <will.deacon at arm.com> wrote:
> On Mon, Apr 15, 2013 at 02:13:55PM +0100, Andre Przywara wrote:
>> On 04/15/2013 11:52 AM, Alexander Spyridakis wrote:
>> > I've run on this problem before, while trying to run KVM guests on A7 cores.
>> >
>> > For some reason the 3rd A7 hangs in arch/arm/kvm/init.S, on the
>> > instruction that updates HSCTLR between the two isbs on __do_hyp_init
>> > (mcr p15, 4, r0, c1, c0, 0). If you boot the system with maxcpus=4 then
>> > init_hyp_mode() will not hang on the A7 cluster. Other than that from my
>> > limited testing KVM on A7 works on a usual linux guest. I also tried to
>> > only boot the 3rd A7 core to rule out any racing issues, but still the
>> > same behaviour applies.
>>
>> Could well be the same issue here. I chased it down till CPU 2 goes into
>> HYP mode to do the initialization.
>> I am running with maxcpus=3 (this increases the likelyhood that
>> kvm_target_cpu() runs on an A15), so CPU #2 is the only one A7.
>> As the HYP mode exception table is empty except for the HVC trap, it may
>> be looping here. I am trying now to get the PC of the faulty instruction.
>
> Yes, it sounds like you're taking a recursive fault because the vectors
> aren't installed yet. Is there any chance you can find out what value you end
> up writing (or trying to write) to the HSCTLR please?
>
Actually I'm a little confused, wasn't Andre seeing a halt on an A15
cpu, not an A7? Or is the theory that an A7 locks up and the calling
A15 hangs on the SMP call to cpu_init_hyp_mode, waiting for the A7 to
complete?

-Christoffer