Re: [PATCH v10 07/21] KVM: ARM64: PMU: Add perf event map and introduce perf event creating function

[Andrew Jones <drjones@redhat.com>]

On Wed, Jan 27, 2016 at 11:51:35AM +0800, Shannon Zhao wrote:
> From: Shannon Zhao <shannon.zhao@linaro.org>
> 
> When we use tools like perf on host, perf passes the event type and the
> id of this event type category to kernel, then kernel will map them to
> hardware event number and write this number to PMU PMEVTYPER<n>_EL0
> register. When getting the event number in KVM, directly use raw event
> type to create a perf_event for it.
> 
> Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/include/asm/pmu.h |   3 ++
>  arch/arm64/kvm/Makefile      |   1 +
>  include/kvm/arm_pmu.h        |  10 ++++
>  virt/kvm/arm/pmu.c           | 122 +++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 136 insertions(+)
>  create mode 100644 virt/kvm/arm/pmu.c
> 
> diff --git a/arch/arm64/include/asm/pmu.h b/arch/arm64/include/asm/pmu.h
> index 4406184..2588f9c 100644
> --- a/arch/arm64/include/asm/pmu.h
> +++ b/arch/arm64/include/asm/pmu.h
> @@ -21,6 +21,7 @@
>  
>  #define ARMV8_MAX_COUNTERS      32
>  #define ARMV8_COUNTER_MASK      (ARMV8_MAX_COUNTERS - 1)
> +#define ARMV8_CYCLE_IDX         (ARMV8_MAX_COUNTERS - 1)

I'm not sure we want to add this. It's name is wrong, as it's really
PMCNTENSET_EL0.C, and just a few lines above we have the idx defined
already (ARMV8_IDX_CYCLE_COUNTER), but as zero, because
arch/arm64/kernel/perf_event.c maps it that way.

I think we should do the same with the pmc array, i.e. map the cycle
counter to idx zero.

>  
>  /*
>   * Per-CPU PMCR: config reg
> @@ -31,6 +32,8 @@
>  #define ARMV8_PMCR_D		(1 << 3) /* CCNT counts every 64th cpu cycle */
>  #define ARMV8_PMCR_X		(1 << 4) /* Export to ETM */
>  #define ARMV8_PMCR_DP		(1 << 5) /* Disable CCNT if non-invasive debug*/
> +/* Determines which PMCCNTR_EL0 bit generates an overflow */
> +#define ARMV8_PMCR_LC		(1 << 6)
>  #define	ARMV8_PMCR_N_SHIFT	11	 /* Number of counters supported */
>  #define	ARMV8_PMCR_N_MASK	0x1f
>  #define	ARMV8_PMCR_MASK		0x3f	 /* Mask for writable bits */
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index caee9ee..122cff4 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -26,3 +26,4 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic-v2-emul.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic-v3.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic-v3-emul.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arch_timer.o
> +kvm-$(CONFIG_KVM_ARM_PMU) += $(KVM)/arm/pmu.o
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index 32fee2d..ee4b15c 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -36,11 +36,21 @@ struct kvm_pmu {
>  };
>  
>  #define kvm_arm_pmu_v3_ready(v)		((v)->arch.pmu.ready)
> +u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx);
> +void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
> +				    u64 select_idx);
>  #else
>  struct kvm_pmu {
>  };
>  
>  #define kvm_arm_pmu_v3_ready(v)		(false)
> +static inline u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu,
> +					    u64 select_idx)
> +{
> +	return 0;
> +}
> +static inline void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu,
> +						  u64 data, u64 select_idx) {}
>  #endif
>  
>  #endif
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> new file mode 100644
> index 0000000..673ec55
> --- /dev/null
> +++ b/virt/kvm/arm/pmu.c
> @@ -0,0 +1,122 @@
> +/*
> + * Copyright (C) 2015 Linaro Ltd.
> + * Author: Shannon Zhao <shannon.zhao@linaro.org>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/cpu.h>
> +#include <linux/kvm.h>
> +#include <linux/kvm_host.h>
> +#include <linux/perf_event.h>
> +#include <asm/kvm_emulate.h>
> +#include <kvm/arm_pmu.h>
> +
> +/**
> + * kvm_pmu_get_counter_value - get PMU counter value
> + * @vcpu: The vcpu pointer
> + * @select_idx: The counter index
> + */
> +u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
> +{
> +	u64 counter, reg, enabled, running;
> +	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> +	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
> +
> +	reg = (select_idx == ARMV8_CYCLE_IDX)
> +	      ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx;

reg = select_idx == 0 ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx - 1;

> +	counter = vcpu_sys_reg(vcpu, reg);
> +
> +	/* The real counter value is equal to the value of counter register plus
> +	 * the value perf event counts.
> +	 */
> +	if (pmc->perf_event)
> +		counter += perf_event_read_value(pmc->perf_event, &enabled,
> +						 &running);
> +
> +	return counter & pmc->bitmask;
> +}
> +
> +/**
> + * kvm_pmu_stop_counter - stop PMU counter
> + * @pmc: The PMU counter pointer
> + *
> + * If this counter has been configured to monitor some event, release it here.
> + */
> +static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc)
> +{
> +	u64 counter, reg;
> +
> +	if (pmc->perf_event) {
> +		counter = kvm_pmu_get_counter_value(vcpu, pmc->idx);
> +		reg = (pmc->idx == ARMV8_CYCLE_IDX)
> +		       ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + pmc->idx;

Second need for this reg selection. We should probably create an idx to
reg function.

> +		vcpu_sys_reg(vcpu, reg) = counter;
> +		perf_event_disable(pmc->perf_event);
> +		perf_event_release_kernel(pmc->perf_event);
> +		pmc->perf_event = NULL;
> +	}
> +}
> +
> +static bool kvm_pmu_counter_is_enabled(struct kvm_vcpu *vcpu, u64 select_idx)
> +{
> +	return (vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMCR_E) &&
> +	       (vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & BIT(select_idx));
> +}
> +
> +/**
> + * 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)
> +{
> +	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;
> +
> +	kvm_pmu_stop_counter(vcpu, pmc);
> +	eventsel = data & ARMV8_EVTYPE_EVENT;
> +
> +	memset(&attr, 0, sizeof(struct perf_event_attr));
> +	attr.type = PERF_TYPE_RAW;
> +	attr.size = sizeof(attr);

nit: the memset sizeof could also just use attr to save characters.
Or why not avoid the memset using struct perf_event_attr attr = {...},
like arch/x86/kvm/pmu.c does?


> +	attr.pinned = 1;
> +	attr.disabled = kvm_pmu_counter_is_enabled(vcpu, select_idx);

hmm.. disabled = enabled ? If we always want it off at set time, then it
should just be '= 1', right?

> +	attr.exclude_user = data & ARMV8_EXCLUDE_EL0 ? 1 : 0;
> +	attr.exclude_kernel = data & ARMV8_EXCLUDE_EL1 ? 1 : 0;
> +	attr.exclude_hv = 1; /* Don't count EL2 events */
> +	attr.exclude_host = 1; /* Don't count host events */
> +	attr.config = eventsel;
> +
> +	counter = kvm_pmu_get_counter_value(vcpu, select_idx);
> +	/* The initial sample period (overflow count) of an event. */
> +	attr.sample_period = (-counter) & pmc->bitmask;
> +
> +	event = perf_event_create_kernel_counter(&attr, -1, current, NULL, pmc);
> +	if (IS_ERR(event)) {
> +		pr_err_once("kvm: pmu event creation failed %ld\n",
> +			    PTR_ERR(event));
> +		return;
> +	}
> +
> +	pmc->perf_event = event;
> +}
> -- 
> 2.0.4
> 
>