KVM: arm64: pmu: Reset sample period on overflow handling (8c3252c0) · Commits · 戴 / test

The PMU emulation code uses the perf event sample period to trigger the overflow detection. This works fine for the *first* overflow handling, but results in a huge number of interrupts on the host, unrelated to the number of interrupts handled in the guest (a x20 factor is pretty common for the cycle counter). On a slow system (such as a SW model), this can result in the guest only making forward progress at a glacial pace. It turns out that the clue is in the name. The sample period is exactly that: a period. And once the an overflow has occured, the following period should be the full width of the associated counter, instead of whatever the guest had initially programed. Reset the sample period to the architected value in the overflow handler, which now results in a number of host interrupts that is much closer to the number of interrupts in the guest. Fixes: ("arm64: KVM: Add PMU overflow interrupt routing") Reviewed-by:

Andrew Murray <andrew.murray@arm.com> Signed-off-by:

Marc Zyngier <maz@kernel.org>

virt/kvm/arm/pmu.c

+20 −0

Original line number	Diff line number	Diff line
		@@ -8,6 +8,7 @@
		#include <linux/kvm.h>
		#include <linux/kvm_host.h>
		#include <linux/perf_event.h>
		#include <linux/perf/arm_pmu.h>
		#include <linux/uaccess.h>
		#include <asm/kvm_emulate.h>
		#include <kvm/arm_pmu.h>
		@@ -442,8 +443,25 @@ static void kvm_pmu_perf_overflow(struct perf_event *perf_event,
		struct pt_regs *regs)
		{
		struct kvm_pmc *pmc = perf_event->overflow_handler_context;
		struct arm_pmu *cpu_pmu = to_arm_pmu(perf_event->pmu);
		struct kvm_vcpu *vcpu = kvm_pmc_to_vcpu(pmc);
		int idx = pmc->idx;
		u64 period;

		cpu_pmu->pmu.stop(perf_event, PERF_EF_UPDATE);

		/*
		* Reset the sample period to the architectural limit,
		* i.e. the point where the counter overflows.
		*/
		period = -(local64_read(&perf_event->count));

		if (!kvm_pmu_idx_is_64bit(vcpu, pmc->idx))
		period &= GENMASK(31, 0);

		local64_set(&perf_event->hw.period_left, 0);
		perf_event->attr.sample_period = period;
		perf_event->hw.sample_period = period;

		__vcpu_sys_reg(vcpu, PMOVSSET_EL0) \|= BIT(idx);

		@@ -451,6 +469,8 @@ static void kvm_pmu_perf_overflow(struct perf_event *perf_event,
		kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
		kvm_vcpu_kick(vcpu);
		}

		cpu_pmu->pmu.start(perf_event, PERF_EF_RELOAD);
		}

		/**

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