Re: [PATCH v2 7/9] KVM: arm/arm64: PMU: remove request-less vcpu kick

[Christoffer Dall <cdall@linaro.org>]

On Fri, Mar 31, 2017 at 06:06:56PM +0200, Andrew Jones wrote:
> Refactor PMU overflow handling in order to remove the request-less
> vcpu kick.  Now, since kvm_vgic_inject_irq() uses vcpu requests,
> there should be no chance that a kick sent at just the wrong time
> (between the VCPU's call to kvm_pmu_flush_hwstate() and before it
> enters guest mode) results in a failure for the guest to see updated
> GIC state until its next exit some time later for some other reason.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  virt/kvm/arm/pmu.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index 69ccce308458..9d725f3afb11 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -203,6 +203,19 @@ static u64 kvm_pmu_overflow_status(struct kvm_vcpu *vcpu)
>  	return reg;
>  }
>  
> +static void kvm_pmu_check_overflow(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> +	bool overflow;
> +
> +	overflow = !!kvm_pmu_overflow_status(vcpu);
> +	if (pmu->irq_level != overflow) {
> +		pmu->irq_level = overflow;
> +		kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id,
> +				    pmu->irq_num, overflow);
> +	}
> +}
> +

If we are changing the way the PMU works to adjust the interrupt
signaling whenever the PMU changes its internal state, do we still ahv
to call kvm_pmu_update_state() from each flush/sync path now?

>  /**
>   * kvm_pmu_overflow_set - set PMU overflow interrupt
>   * @vcpu: The vcpu pointer
> @@ -210,31 +223,19 @@ static u64 kvm_pmu_overflow_status(struct kvm_vcpu *vcpu)
>   */
>  void kvm_pmu_overflow_set(struct kvm_vcpu *vcpu, u64 val)
>  {
> -	u64 reg;
> -
>  	if (val == 0)
>  		return;
>  
>  	vcpu_sys_reg(vcpu, PMOVSSET_EL0) |= val;
> -	reg = kvm_pmu_overflow_status(vcpu);
> -	if (reg != 0)
> -		kvm_vcpu_kick(vcpu);
> +	kvm_pmu_check_overflow(vcpu);
>  }
>  
>  static void kvm_pmu_update_state(struct kvm_vcpu *vcpu)
>  {
> -	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> -	bool overflow;
> -
>  	if (!kvm_arm_pmu_v3_ready(vcpu))
>  		return;
>  
> -	overflow = !!kvm_pmu_overflow_status(vcpu);
> -	if (pmu->irq_level != overflow) {
> -		pmu->irq_level = overflow;
> -		kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id,
> -				    pmu->irq_num, overflow);
> -	}
> +	kvm_pmu_check_overflow(vcpu);
>  }
>  
>  /**
> -- 
> 2.9.3
> 

Thanks,
-Christoffer