Re: [PATCH v2 3/5] KVM: arm/arm64: re-create event when setting counter value

[Julien Thierry <julien.thierry@arm.com>]

Hi Andrew,

On 04/02/2019 16:53, Andrew Murray wrote:
> The perf event sample_period is currently set based upon the current
> counter value, when PMXEVTYPER is written to and the perf event is created.
> However the user may choose to write the type before the counter value in
> which case sample_period will be set incorrectly. Let's instead decouple
> event creation from PMXEVTYPER and (re)create the event in either
> suitation.
> 
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
>  virt/kvm/arm/pmu.c | 40 +++++++++++++++++++++++++++++++---------
>  1 file changed, 31 insertions(+), 9 deletions(-)
> 
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index 6e7c179..95d74ec 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -24,6 +24,7 @@
>  #include <kvm/arm_pmu.h>
>  #include <kvm/arm_vgic.h>
>  
> +static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx);
>  /**
>   * kvm_pmu_get_counter_value - get PMU counter value
>   * @vcpu: The vcpu pointer
> @@ -62,6 +63,9 @@ void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
>  	reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
>  	      ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx;
>  	__vcpu_sys_reg(vcpu, reg) += (s64)val - kvm_pmu_get_counter_value(vcpu, select_idx);
> +
> +	/* Recreate the perf event to reflect the updated sample_period */
> +	kvm_pmu_create_perf_event(vcpu, select_idx);
>  }
>  
>  /**
> @@ -378,23 +382,22 @@ static bool kvm_pmu_counter_is_enabled(struct kvm_vcpu *vcpu, u64 select_idx)
>  }
>  
>  /**
> - * kvm_pmu_set_counter_event_type - set selected counter to monitor some event
> + * kvm_pmu_create_perf_event - create a perf event for a counter
>   * @vcpu: The vcpu pointer
> - * @data: The data guest writes to PMXEVTYPER_EL0
> + * @data: Type of event as per PMXEVTYPER_EL0 format
>   * @select_idx: The number of selected counter
> - *
> - * When OS accesses PMXEVTYPER_EL0, that means it wants to set a PMC to count an
> - * event with given hardware event number. Here we call perf_event API to
> - * emulate this action and create a kernel perf event for it.
>   */
> -void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
> -				    u64 select_idx)
> +static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
>  {
>  	struct kvm_pmu *pmu = &vcpu->arch.pmu;
>  	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
>  	struct perf_event *event;
>  	struct perf_event_attr attr;
> -	u64 eventsel, counter;
> +	u64 eventsel, counter, reg, data;
> +
> +	reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
> +	      ? PMCCFILTR_EL0 : PMEVTYPER0_EL0 + select_idx;
> +	data = __vcpu_sys_reg(vcpu, reg);
>  
>  	kvm_pmu_stop_counter(vcpu, pmc);
>  	eventsel = data & ARMV8_PMU_EVTYPE_EVENT;
> @@ -431,6 +434,25 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
>  	pmc->perf_event = event;
>  }
>  
> +/**
> + * kvm_pmu_set_counter_event_type - set selected counter to monitor some event
> + * @vcpu: The vcpu pointer
> + * @data: The data guest writes to PMXEVTYPER_EL0
> + * @select_idx: The number of selected counter
> + *
> + * When OS accesses PMXEVTYPER_EL0, that means it wants to set a PMC to count an
> + * event with given hardware event number. Here we call perf_event API to
> + * emulate this action and create a kernel perf event for it.
> + */
> +void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
> +				    u64 select_idx)
> +{
> +	u64 event_type = data & ARMV8_PMU_EVTYPE_MASK;
> +> +	__vcpu_sys_reg(vcpu, PMEVTYPER0_EL0 + select_idx) = event_type;

I think there has been a wrong split. In the next patch you add the
check for the cycle counter but I believe it should be already present here.

With that fixed:

Reviewed-by: Julien Thierry <julien.thierry@arm.com>

> +	kvm_pmu_create_perf_event(vcpu, select_idx);
> +}
> +
>  bool kvm_arm_support_pmu_v3(void)
>  {
>  	/*
> 

-- 
Julien Thierry