linux-kernel - Re: [RFC 1/3] KVM: arm64: pmu: Don't increment SW

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Date:   Fri, 6 Dec 2019 10:35:05 +0000
From:   Andrew Murray <andrew.murray@....com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, maz@...nel.org,
        linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        james.morse@....com, suzuki.poulose@....com, drjones@...hat.com
Subject: Re: [RFC 1/3] KVM: arm64: pmu: Don't increment SW_INCR if PMCR.E is
 unset

On Wed, Dec 04, 2019 at 09:44:24PM +0100, Eric Auger wrote:
> The specification says PMSWINC increments PMEVCNTR<n>_EL1 by 1
> if PMEVCNTR<n>_EL0 is enabled and configured to count SW_INCR.
> 
> For PMEVCNTR<n>_EL0 to be enabled, we need both PMCNTENSET to
> be set for the corresponding event counter but we also need
> the PMCR.E bit to be set.
> 
> Fixes: 7a0adc7064b8 ("arm64: KVM: Add access handler for PMSWINC register")
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> ---
>  virt/kvm/arm/pmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index 8731dfeced8b..c3f8b059881e 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -486,6 +486,9 @@ void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
>  	if (val == 0)
>  		return;
>  
> +	if (!(__vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_E))
> +		return;
> +

Reviewed-by: Andrew Murray <andrew.murray@....com>


>  	enable = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
>  	for (i = 0; i < ARMV8_PMU_CYCLE_IDX; i++) {
>  		if (!(val & BIT(i)))
> -- 
> 2.20.1
>