[PATCH 3/9] KVM: arm64: PMU: Only narrow counters that are not 64bit wide

[Reiji Watanabe]

Hi Marc,

On Fri, Aug 5, 2022 at 6:58 AM Marc Zyngier <maz at kernel.org> wrote:
>
> The current PMU emulation sometimes narrows counters to 32bit
> if the counter isn't the cycle counter. As this is going to
> change with PMUv3p5 where the counters are all 64bit, only
> perform the narrowing on 32bit counters.
>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/pmu-emul.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index 9040d3c80096..0ab6f59f433c 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -149,22 +149,22 @@ static void kvm_pmu_release_perf_event(struct kvm_pmc *pmc)
>   */
>  static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc)
>  {
> -       u64 counter, reg, val;
> +       u64 counter, reg;
>
>         if (!pmc->perf_event)
>                 return;
>
>         counter = kvm_pmu_get_counter_value(vcpu, pmc->idx);
>
> -       if (pmc->idx == ARMV8_PMU_CYCLE_IDX) {
> +       if (pmc->idx == ARMV8_PMU_CYCLE_IDX)
>                 reg = PMCCNTR_EL0;
> -               val = counter;
> -       } else {
> +       else
>                 reg = PMEVCNTR0_EL0 + pmc->idx;
> -               val = lower_32_bits(counter);
> -       }
>
> -       __vcpu_sys_reg(vcpu, reg) = val;
> +       if (!kvm_pmu_idx_is_64bit(vcpu, pmc->idx))
> +               counter = lower_32_bits(counter);

It appears that narrowing the counter to 32bit here is unnecessary
because it is already done by kvm_pmu_get_counter_value().

Thank you,
Reiji

> +
> +       __vcpu_sys_reg(vcpu, reg) = counter;
>
>         kvm_pmu_release_perf_event(pmc);
>  }
> @@ -417,7 +417,8 @@ static void kvm_pmu_counter_increment(struct kvm_vcpu *vcpu,
>
>                 /* Increment this counter */
>                 reg = __vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) + 1;
> -               reg = lower_32_bits(reg);
> +               if (!kvm_pmu_idx_is_64bit(vcpu, i))
> +                       reg = lower_32_bits(reg);
>                 __vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) = reg;
>
>                 if (reg) /* No overflow? move on */
> --
> 2.34.1
>
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