Re: [PATCH 09/18] KVM: ARM64: Add reset and access handlers for PMXEVCNTR_EL0 register

[Christoffer Dall <christoffer.dall@linaro.org>]

On Mon, Jul 06, 2015 at 10:17:39AM +0800, shannon.zhao@linaro.org wrote:
> From: Shannon Zhao <shannon.zhao@linaro.org>
> 
> Since the reset value of PMXEVTYPER_EL0 is UNKNOWN, use reset_unknown
> for its reset handler. Add access handler which emulates writing and
> reading PMXEVTYPER_EL0 register. When reading PMXEVCNTR_EL0, call
> perf_event_read_value to get the count value of the perf event.
> 
> Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 21 ++++++++++++++++++++-
>  include/kvm/arm_pmu.h     | 11 +++++++++++
>  virt/kvm/arm/pmu.c        | 37 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 68 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index b4f8dd9..2bcf1a0 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -356,6 +356,25 @@ static bool access_pmxevtyper(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +static bool access_pmxevcntr(struct kvm_vcpu *vcpu,
> +			     const struct sys_reg_params *p,
> +			     const struct sys_reg_desc *r)
> +{
> +	unsigned long val;
> +
> +	if (p->is_write) {
> +		val = *vcpu_reg(vcpu, p->Rt);
> +		kvm_pmu_set_counter_value(vcpu, vcpu_sys_reg(vcpu, PMSELR_EL0),
> +					  val & 0xffffffffUL);
> +	} else {
> +		val = kvm_pmu_get_counter_value(vcpu,
> +						vcpu_sys_reg(vcpu, PMSELR_EL0));
> +		*vcpu_reg(vcpu, p->Rt) = val;
> +	}
> +
> +	return true;
> +}
> +
>  /* Silly macro to expand the DBG{BCR,BVR,WVR,WCR}n_EL1 registers in one go */
>  #define DBG_BCR_BVR_WCR_WVR_EL1(n)					\
>  	/* DBGBVRn_EL1 */						\
> @@ -577,7 +596,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	  access_pmxevtyper, reset_unknown, PMXEVTYPER_EL0 },
>  	/* PMXEVCNTR_EL0 */
>  	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1101), Op2(0b010),
> -	  trap_raz_wi },
> +	  access_pmxevcntr, reset_unknown, PMXEVCNTR_EL0 },
>  	/* PMUSERENR_EL0 */
>  	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1110), Op2(0b000),
>  	  trap_raz_wi },
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index 1050b24..40ab4a0 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -45,11 +45,22 @@ struct kvm_pmu {
>  
>  #ifdef CONFIG_KVM_ARM_PMU
>  void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu);
> +void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, unsigned long select_idx,
> +			       unsigned long val);
> +unsigned long kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu,
> +					unsigned long select_idx);
>  void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, unsigned long data,
>  				    unsigned long select_idx);
>  void kvm_pmu_init(struct kvm_vcpu *vcpu);
>  #else
>  static inline void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu) {}
> +void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, unsigned long select_idx,
> +			       unsigned long val) {}
> +unsigned long kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu,
> +					unsigned long select_idx)
> +{
> +	return 0;
> +}
>  void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, unsigned long data,
>  				    unsigned long select_idx) {}
>  static inline void kvm_pmu_init(struct kvm_vcpu *vcpu) {}
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index 50a3c82..361fa51 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -97,6 +97,43 @@ void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu)
>  }
>  
>  /**
> + * kvm_pmu_set_counter_value - set PMU counter value
> + * @vcpu: The vcpu pointer
> + * @select_idx: The counter index
> + * @val: the value to be set
> + */
> +void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, unsigned long select_idx,
> +			       unsigned long val)
> +{
> +	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> +	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
> +
> +	pmc->counter = val;

how does this help generate an overflow event when expected?

> +}
> +
> +/**
> + * kvm_pmu_set_counter_value - set PMU counter value

s/set/get/

> + * @vcpu: The vcpu pointer
> + * @select_idx: The counter index
> + *
> + * Call perf_event API to get the event count
> + */
> +unsigned long kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu,
> +					unsigned long select_idx)
> +{
> +	u64 enabled, running;
> +	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> +	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
> +	unsigned long counter = pmc->counter;
> +
> +	if (pmc->perf_event) {
> +		counter += perf_event_read_value(pmc->perf_event,
> +						&enabled, &running);

I don't quite understand the summation here or feel convinced that
enabled and running should be simply thrown away.

Can you explain this, potentially in the kdocs above...

> +	}
> +	return counter;
> +}
> +
> +/**
>   * kvm_pmu_find_hw_event - find hardware event
>   * @pmu: The pmu pointer
>   * @event_select: The number of selected event type
> -- 
> 2.1.0
>