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

From: [email-masked] (Christoffer Dall)
Date: Fri, 21 Mar 2014 16:37:15 -0700

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 <[email-masked]>
> Signed-off-by: Pranavkumar Sawargaonkar <[email-masked]>
> ---
>  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.

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

> +
> +	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