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Subject[PATCH] KVM: ARM64: Update perf event when setting PMU count value
Date
Guest will adjust the sample period and set PMU counter value when
it takes a long time to handle the PMU interrupts.

However, we don't have a corresponding change on the virtual PMU
which is emulated via a perf event. It could cause a large number
of PMU interrupts injected to guest. Then guest will get hang for
handling these interrupts.

So update the sample_period of perf event if the counter value is
changed to avoid this case.

Signed-off-by: Xiang Zheng <zhengxiang9@huawei.com>
---
virt/kvm/arm/pmu.c | 54 +++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 45 insertions(+), 9 deletions(-)

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index 1c5b76c..cbad3ec 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -24,6 +24,11 @@
#include <kvm/arm_pmu.h>
#include <kvm/arm_vgic.h>

+static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc);
+static struct perf_event *kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu,
+ struct kvm_pmc *pmc,
+ struct perf_event_attr *attr);
+
/**
* kvm_pmu_get_counter_value - get PMU counter value
* @vcpu: The vcpu pointer
@@ -57,11 +62,29 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
*/
void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
{
- u64 reg;
+ u64 reg, counter, old_sample_period;
+ struct kvm_pmu *pmu = &vcpu->arch.pmu;
+ struct kvm_pmc *pmc = &pmu->pmc[select_idx];
+ struct perf_event *event;
+ struct perf_event_attr attr;

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);
+
+ if (pmc->perf_event) {
+ attr = pmc->perf_event->attr;
+ old_sample_period = attr.sample_period;
+ counter = kvm_pmu_get_counter_value(vcpu, select_idx);
+ attr.sample_period = (-counter) & pmc->bitmask;
+ if (attr.sample_period == old_sample_period)
+ return;
+
+ kvm_pmu_stop_counter(vcpu, pmc);
+ event = kvm_pmu_create_perf_event(vcpu, pmc, &attr);
+ if (event)
+ pmc->perf_event = event;
+ }
}

/**
@@ -303,6 +326,24 @@ static void kvm_pmu_perf_overflow(struct perf_event *perf_event,
}
}

+static struct perf_event *kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu,
+ struct kvm_pmc *pmc,
+ struct perf_event_attr *attr)
+{
+ struct perf_event *event;
+
+ event = perf_event_create_kernel_counter(attr, -1, current,
+ kvm_pmu_perf_overflow, pmc);
+
+ if (IS_ERR(event)) {
+ pr_err_once("kvm: pmu event creation failed %ld\n",
+ PTR_ERR(event));
+ return NULL;
+ }
+
+ return event;
+}
+
/**
* kvm_pmu_software_increment - do software increment
* @vcpu: The vcpu pointer
@@ -416,15 +457,10 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
/* The initial sample period (overflow count) of an event. */
attr.sample_period = (-counter) & pmc->bitmask;

- event = perf_event_create_kernel_counter(&attr, -1, current,
- kvm_pmu_perf_overflow, pmc);
- if (IS_ERR(event)) {
- pr_err_once("kvm: pmu event creation failed %ld\n",
- PTR_ERR(event));
- return;
- }
+ event = kvm_pmu_create_perf_event(vcpu, pmc, &attr);

- pmc->perf_event = event;
+ if (event)
+ pmc->perf_event = event;
}

bool kvm_arm_support_pmu_v3(void)
--
1.8.3.1

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