[PATCH v7 11/12] ARM/ARM64: KVM: Emulate PSCI v0.2 CPU_SUSPEND

[Anup Patel]

On 3 April 2014 02:33, Christoffer Dall <christoffer.dall at linaro.org> wrote:
> On Wed, Apr 02, 2014 at 04:12:26PM +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 we only 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
>> and WAKEUP events for KVM ARM/ARM64.
>>
>> Due to above, we implement CPU_SUSPEND emulation similar to WFI
>> (Wait-for-interrupt) emulation and we also treat power-down request
>> to be same as stand-by request. This is also consistent with section
>> 5.4.1 and section 5.4.2 of PSCI v0.2 specification.
>>
>> Signed-off-by: Anup Patel <anup.patel at linaro.org>
>> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar at linaro.org>
>> ---
>>  arch/arm/kvm/psci.c |   27 +++++++++++++++++++++++----
>>  1 file changed, 23 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
>> index fdbd829..74fa4ad 100644
>> --- a/arch/arm/kvm/psci.c
>> +++ b/arch/arm/kvm/psci.c
>> @@ -52,6 +52,25 @@ 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
>> +      * so for simplicity we make VCPU suspend emulation to be
>> +      * same-as WFI (Wait-for-interrupt) emulation. This is also
>> +      * consistent with intended use of StateID as described in
>> +      * section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A).
>
> The WFI implementation wakes up on interrupts, so we are inherently
> defining that as a wakeup event for KVM with this patch, so the comment
> should be adjusted accordingly.

Sure, I will update the comment.

--
Anup

>
> -Christoffer
>
>> +      *
>> +      * Further, we also treat power-down request to be same as
>> +      * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2
>> +      * specification (ARM DEN 0022A). This means all suspend states
>> +      * for KVM PSCI emulation will preserve the register state.
>> +      */
>> +     kvm_vcpu_block(vcpu);
>> +
>> +     return PSCI_RET_SUCCESS;
>> +}
>> +
>>  static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
>>  {
>>       vcpu->arch.pause = true;
>> @@ -195,6 +214,10 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
>>                */
>>               val = 2;
>>               break;
>> +     case PSCI_0_2_FN_CPU_SUSPEND:
>> +     case PSCI_0_2_FN64_CPU_SUSPEND:
>> +             val = kvm_psci_vcpu_suspend(vcpu);
>> +             break;
>>       case PSCI_0_2_FN_CPU_OFF:
>>               kvm_psci_vcpu_off(vcpu);
>>               val = PSCI_RET_SUCCESS;
>> @@ -232,10 +255,6 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
>>               val = PSCI_RET_SUCCESS;
>>               ret = 0;
>>               break;
>> -     case PSCI_0_2_FN_CPU_SUSPEND:
>> -     case PSCI_0_2_FN64_CPU_SUSPEND:
>> -             val = PSCI_RET_NOT_SUPPORTED;
>> -             break;
>>       default:
>>               return -EINVAL;
>>       }
>> --
>> 1.7.9.5
>>