Re: [PATCH 1/2] KVM: arm: rename pause into power_off

[Christoffer Dall <christoffer.dall@linaro.org>]

On Mon, Jul 06, 2015 at 02:49:55PM +0200, Eric Auger wrote:
> The kvm_vcpu_arch pause field is renamed into power_off to prepare
> for the introduction of a new pause field.
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> 
> v4 -> v5:
> - fix compilation issue on arm64 (add power_off field in kvm_host.h)
> ---
>  arch/arm/include/asm/kvm_host.h   |  4 ++--
>  arch/arm/kvm/arm.c                | 10 +++++-----
>  arch/arm/kvm/psci.c               | 10 +++++-----
>  arch/arm64/include/asm/kvm_host.h |  4 ++--
>  4 files changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index e896d2c..304004d 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -129,8 +129,8 @@ struct kvm_vcpu_arch {
>  	 * here.
>  	 */
>  
> -	/* Don't run the guest on this vcpu */
> -	bool pause;
> +	/* vcpu power-off state */
> +	bool power_off;
>  
>  	/* IO related fields */
>  	struct kvm_decode mmio_decode;
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index bcdf799..7537e68 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -475,7 +475,7 @@ static void vcpu_pause(struct kvm_vcpu *vcpu)
>  {
>  	wait_queue_head_t *wq = kvm_arch_vcpu_wq(vcpu);
>  
> -	wait_event_interruptible(*wq, !vcpu->arch.pause);
> +	wait_event_interruptible(*wq, !vcpu->arch.power_off);

would there be any benefit to simply calling kvm_vcpu_block() instead of
vcpu_pause, and rewrite kvm_arch_vcpu_runnable to:

int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
{
▸       return !vcpu->arch.power_off &&
		(!!v->arch.irq_lines || kvm_vgic_vcpu_pending_irq(v));
}

Not sure really, certainly the runnable function does not become more
readable.

>  }
>  
>  static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
> @@ -525,7 +525,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  
>  		update_vttbr(vcpu->kvm);
>  
> -		if (vcpu->arch.pause)
> +		if (vcpu->arch.power_off)
>  			vcpu_pause(vcpu);

looking back over this code, how does this actually guarantee that we
don't run a powered-off cpu?

vcpu_pause() just does a wait_event_interruptible(), so if we get
scheduled again, we'll just proceed running.  Is there any case where we
could get scheduled without signal_pending() being true and therefore
inadvertedly run the vcpu?

if so, we should change the line below like this:

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index bc738d2..98f31e6 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -542,7 +542,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 			run->exit_reason = KVM_EXIT_INTR;
 		}
 
-		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm)) {
+		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
+		    vcpu->arch.power_off) {
 			local_irq_enable();
 			preempt_enable();
 			kvm_timer_sync_hwstate(vcpu);


Sorry for polluting your patch with these questions, I'm otherwise fine
with the rename.

Thanks,
-Christoffer

>  
>  		/*
> @@ -766,12 +766,12 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
>  	vcpu_reset_hcr(vcpu);
>  
>  	/*
> -	 * Handle the "start in power-off" case by marking the VCPU as paused.
> +	 * Handle the "start in power-off" case.
>  	 */
>  	if (test_bit(KVM_ARM_VCPU_POWER_OFF, vcpu->arch.features))
> -		vcpu->arch.pause = true;
> +		vcpu->arch.power_off = true;
>  	else
> -		vcpu->arch.pause = false;
> +		vcpu->arch.power_off = false;
>  
>  	return 0;
>  }
> diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
> index 4b94b51..134971a 100644
> --- a/arch/arm/kvm/psci.c
> +++ b/arch/arm/kvm/psci.c
> @@ -63,7 +63,7 @@ static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
>  
>  static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
>  {
> -	vcpu->arch.pause = true;
> +	vcpu->arch.power_off = true;
>  }
>  
>  static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
> @@ -87,7 +87,7 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
>  	 */
>  	if (!vcpu)
>  		return PSCI_RET_INVALID_PARAMS;
> -	if (!vcpu->arch.pause) {
> +	if (!vcpu->arch.power_off) {
>  		if (kvm_psci_version(source_vcpu) != KVM_ARM_PSCI_0_1)
>  			return PSCI_RET_ALREADY_ON;
>  		else
> @@ -115,7 +115,7 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
>  	 * the general puspose registers are undefined upon CPU_ON.
>  	 */
>  	*vcpu_reg(vcpu, 0) = context_id;
> -	vcpu->arch.pause = false;
> +	vcpu->arch.power_off = false;
>  	smp_mb();		/* Make sure the above is visible */
>  
>  	wq = kvm_arch_vcpu_wq(vcpu);
> @@ -152,7 +152,7 @@ static unsigned long kvm_psci_vcpu_affinity_info(struct kvm_vcpu *vcpu)
>  	kvm_for_each_vcpu(i, tmp, kvm) {
>  		mpidr = kvm_vcpu_get_mpidr_aff(tmp);
>  		if (((mpidr & target_affinity_mask) == target_affinity) &&
> -		    !tmp->arch.pause) {
> +		    !tmp->arch.power_off) {
>  			return PSCI_0_2_AFFINITY_LEVEL_ON;
>  		}
>  	}
> @@ -175,7 +175,7 @@ static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type)
>  	 * re-initialized.
>  	 */
>  	kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> -		tmp->arch.pause = true;
> +		tmp->arch.power_off = true;
>  		kvm_vcpu_kick(tmp);
>  	}
>  
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 2709db2..009da6b 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -122,8 +122,8 @@ struct kvm_vcpu_arch {
>  	 * here.
>  	 */
>  
> -	/* Don't run the guest */
> -	bool pause;
> +	/* vcpu power-off state */
> +	bool power_off;
>  
>  	/* IO related fields */
>  	struct kvm_decode mmio_decode;
> -- 
> 1.9.1
> 
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