[PATCH] arm64: KVM: Support Cortex-A57 guest CPU on APM X-Gene host

[Anup Patel]

On Wed, Jul 3, 2013 at 7:29 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
> On 03/07/13 11:54, Peter Maydell wrote:
>> On 3 July 2013 09:42, Anup Patel <anup.patel at linaro.org> wrote:
>>> Update kvm_target_cpu() to allow Cortex-A57 guest CPU on APM X-Gene.
>>>
>>> Signed-off-by: Anup Patel <anup.patel at linaro.org>
>>> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar at linaro.org>
>>> ---
>>>  arch/arm64/kvm/guest.c |   10 ++++++++--
>>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
>>> index 2c3ff67..765f56f 100644
>>> --- a/arch/arm64/kvm/guest.c
>>> +++ b/arch/arm64/kvm/guest.c
>>> @@ -207,8 +207,13 @@ int __attribute_const__ kvm_target_cpu(void)
>>>         unsigned long implementor = read_cpuid_implementor();
>>>         unsigned long part_number = read_cpuid_part_number();
>>>
>>> -       if (implementor != ARM_CPU_IMP_ARM)
>>> -               return -EINVAL;
>>> +       switch (implementor) {
>>> +       case ARM_CPU_IMP_ARM:
>>> +       case ARM_CPU_IMP_APM:
>>> +               break;
>>> +       default:
>>> +               return -EINVAL;
>>> +       }
>>
>> Doesn't this change mean we now accept the below part
>> numbers for all implementors? That doesn't look right.
>>
>>>         switch (part_number) {
>>>         case ARM_CPU_PART_AEM_V8:
>>> @@ -216,6 +221,7 @@ int __attribute_const__ kvm_target_cpu(void)
>>>         case ARM_CPU_PART_FOUNDATION:
>>>                 return KVM_ARM_TARGET_FOUNDATION_V8;
>>>         case ARM_CPU_PART_CORTEX_A57:
>>> +       case APM_CPU_PART_POTENZA:
>>>                 /* Currently handled by the generic backend */
>>>                 return KVM_ARM_TARGET_CORTEX_A57;
>>>         default:
>>
>> Do we really model all the system registers and so on correctly
>> sufficiently to be able to present the guest with an A57 vcpu
>> on an APM X-Gene host? (ie without accidentally leaking the
>> host ID registers/system registers/impdef registers to the
>> guest).
>
> There is no such thing in the KVM/arm64 code. The guest sees the real
> host, and I really don't lie the idea of lying to userspace by
> pretending that we're going to emulate an A57.
>
> Anup: I suggest you rework that patch to present a X-Gene vcpu. You can
> implement it by declaring a new target and implementing it in terms of
> the generic backend one if that's convenient. But just pretending this
> is an A57 is not going to fly, sorry.

Sure, I will add separate target vcpu for X-Gene and try to re-use your
generic backend.

>
> Cheers,
>
>         M.
> --
> Jazz is not dead. It just smells funny...
>
>
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--Anup