[PATCH v5 10/11] ARM/ARM64: KVM: Emulate PSCI v0.2 CPU_SUSPEND

[Anup Patel]

On 22 March 2014 05:07, Christoffer Dall <christoffer.dall at linaro.org> wrote:
> On Fri, Mar 21, 2014 at 06:23:33PM +0530, Anup Patel wrote:
>> This patch adds emulation of PSCI v0.2 CPU_SUSPEND function call for
>> KVM ARM/ARM64. This is a CPU-level function call which can suspend
>> current CPU or current CPU cluster. We don't have VCPU clusters in
>> KVM so for KVM we simply suspend the current VCPU.
>>
>> The CPU_SUSPEND emulation is not tested much because currently there
>> is no CPUIDLE driver in Linux kernel that uses PSCI CPU_SUSPEND. The
>> PSCI CPU_SUSPEND implementation in ARM64 kernel was tested using a
>> Simple CPUIDLE driver which is not published due to unstable DT-bindings
>> for PSCI.
>> (For more info, http://lwn.net/Articles/574950/)
>>
>> Even if we had stable DT-bindings for PSCI and CPUIDLE driver that
>> uses PSCI CPU_SUSPEND then still we need to define SUSPEND states
>> for KVM ARM/ARM64.
>>
>> Due to this, the CPU_SUSPEND emulation added by this patch only pause
>> current VCPU and to wakeup a suspended VCPU we need to explicity call
>> PSCI CPU_ON from Guest.
>>
>> Signed-off-by: Anup Patel <anup.patel at linaro.org>
>> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar at linaro.org>
>> ---
>>  arch/arm/kvm/psci.c |   24 ++++++++++++++++++++----
>>  1 file changed, 20 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
>> index 1e85452..e32ad10 100644
>> --- a/arch/arm/kvm/psci.c
>> +++ b/arch/arm/kvm/psci.c
>> @@ -52,6 +52,22 @@ static unsigned long psci_affinity_mask(unsigned long affinity_level)
>>       return affinity_mask;
>>  }
>>
>> +static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
>> +{
>> +     /*
>> +      * NOTE: Currently, we don't have any wakeup events for KVM
>> +      * hence VCPU suspend turns-out to be same as VCPU off request.
>> +      * This means to suspend a VCPU we simply set the pause flag
>> +      * and update VCPU registers as-per wakeup parameters provided
>> +      * via r2 & r3 (or x2 & x3).
>> +      */
>> +     vcpu->arch.pause = true;
>> +     *vcpu_pc(vcpu) = *vcpu_reg(vcpu, 2);
>> +     *vcpu_reg(vcpu, 0) = *vcpu_reg(vcpu, 3);
>
> But the spec states in Section 5.1.2 that if Bit[16] StateType == 0,
> then the entry point and context_id parameters are ignored, because all
> state is retained for a standby state.

OK, I will update this accordingly.

>
> I think Mark Rutland commented that KVM should define at last interrupts
> to the CPU as a wakeup event.

How about using kvm_vcpu_block(vcpu) instead of "vcpu->arch.pause = true"?

This will make CPU_SUSPEND emulation very similar to WFI emulation.

Regards,
Anup

>
>> +
>> +     return KVM_PSCI_RET_SUCCESS;
>> +}
>> +
>>  static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
>>  {
>>       vcpu->arch.pause = true;
>> @@ -195,6 +211,10 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
>>                */
>>               val = 2;
>>               break;
>> +     case KVM_PSCI_0_2_FN_CPU_SUSPEND:
>> +     case KVM_PSCI_0_2_FN64_CPU_SUSPEND:
>> +             val = kvm_psci_vcpu_suspend(vcpu);
>> +             break;
>>       case KVM_PSCI_0_2_FN_CPU_OFF:
>>               kvm_psci_vcpu_off(vcpu);
>>               val = KVM_PSCI_RET_SUCCESS;
>> @@ -232,10 +252,6 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
>>               val = KVM_PSCI_RET_SUCCESS;
>>               ret = 0;
>>               break;
>> -     case KVM_PSCI_0_2_FN_CPU_SUSPEND:
>> -     case KVM_PSCI_0_2_FN64_CPU_SUSPEND:
>> -             val = KVM_PSCI_RET_NI;
>> -             break;
>>       default:
>>               return -EINVAL;
>>       }
>> --
>> 1.7.9.5
>>
>
> Thanks,
> -Christoffer
>