Hi Marc,
On Sun, Nov 13, 2022 at 8:38 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> Even when using PMUv3p5 (which implies 64bit counters), there is
> no way for AArch32 to write to the top 32 bits of the counters.
> The only way to influence these bits (other than by counting
> events) is by writing PMCR.P==1.
>
> Make sure we obey the architecture and preserve the top 32 bits
> on a counter update.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/kvm/pmu-emul.c | 35 +++++++++++++++++++++++++++--------
> 1 file changed, 27 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index ea0c8411641f..419e5e0a13d0 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -119,13 +119,8 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
> return counter;
> }
>
> -/**
> - * kvm_pmu_set_counter_value - set PMU counter value
> - * @vcpu: The vcpu pointer
> - * @select_idx: The counter index
> - * @val: The counter value
> - */
> -void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
> +static void kvm_pmu_set_counter(struct kvm_vcpu *vcpu, u64 select_idx, u64 val,
> + bool force)
> {
> u64 reg;
>
> @@ -135,12 +130,36 @@ void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
> kvm_pmu_release_perf_event(&vcpu->arch.pmu.pmc[select_idx]);
>
> reg = counter_index_to_reg(select_idx);
> +
> + if (vcpu_mode_is_32bit(vcpu) && select_idx != ARMV8_PMU_CYCLE_IDX &&
> + !force) {
> + /*
> + * Even with PMUv3p5, AArch32 cannot write to the top
> + * 32bit of the counters. The only possible course of
> + * action is to use PMCR.P, which will reset them to
> + * 0 (the only use of the 'force' parameter).
> + */
> + val = lower_32_bits(val);
> + val |= upper_32_bits(__vcpu_sys_reg(vcpu, reg));
Shouldn't the result of upper_32_bits() be shifted 32bits left
before ORing (to maintain the upper 32bits of the current value) ?
Thank you,
Reiji
> + }
> +
> __vcpu_sys_reg(vcpu, reg) = val;
>
> /* Recreate the perf event to reflect the updated sample_period */
> kvm_pmu_create_perf_event(vcpu, select_idx);
> }
>
> +/**
> + * kvm_pmu_set_counter_value - set PMU counter value
> + * @vcpu: The vcpu pointer
> + * @select_idx: The counter index
> + * @val: The counter value
> + */
> +void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
> +{
> + kvm_pmu_set_counter(vcpu, select_idx, val, false);
> +}
> +
> /**
> * kvm_pmu_release_perf_event - remove the perf event
> * @pmc: The PMU counter pointer
> @@ -533,7 +552,7 @@ void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
> unsigned long mask = kvm_pmu_valid_counter_mask(vcpu);
> mask &= ~BIT(ARMV8_PMU_CYCLE_IDX);
> for_each_set_bit(i, &mask, 32)
> - kvm_pmu_set_counter_value(vcpu, i, 0);
> + kvm_pmu_set_counter(vcpu, i, 0, true);
> }
> }
>
> --
> 2.34.1
>
