[PATCH v4 05/16] KVM: arm64: PMU: Narrow the overflow checking when required

[Reiji Watanabe]

On Sun, Nov 13, 2022 at 8:38 AM Marc Zyngier <maz at kernel.org> wrote:
>
> For 64bit counters that overflow on a 32bit boundary, make
> sure we only check the bottom 32bit to generate a CHAIN event.
>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/pmu-emul.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index d050143326b5..9e6bc7edc4de 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -417,7 +417,8 @@ static void kvm_pmu_counter_increment(struct kvm_vcpu *vcpu,
>                 reg = lower_32_bits(reg);
>                 __vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) = reg;
>
> -               if (reg) /* No overflow? move on */
> +               /* No overflow? move on */
> +               if (kvm_pmu_idx_has_64bit_overflow(vcpu, i) ? reg : lower_32_bits(reg))

A few lines up, the 'reg' is unconditionally updated with
"lower_32_bits(reg)". So, the change initially confused me
(until I checked the following patch).  IMHO it might be more
clear if this patch and the next patch are folded into one patch.

Anyway:
Reviewed-by: Reiji Watanabe <reijiw at google.com>

Thank you,
Reiji



>                         continue;
>
>                 /* Mark overflow */
> --
> 2.34.1
>