From 671bd9934a861288a248b051751061b11654aef9 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Fri, 18 Apr 2014 03:35:08 +0300 Subject: KVM: x86: Fix wrong/stuck PMU when guest does not use PMI If a guest enables a performance counter but does not enable PMI, the hypervisor currently does not reprogram the performance counter once it overflows. As a result the host performance counter is kept with the original sampling period which was configured according to the value of the guest's counter when the counter was enabled. Such behaviour can cause very bad consequences. The most distrubing one can cause the guest not to make any progress at all, and keep exiting due to host PMI before any guest instructions is exeucted. This situation occurs when the performance counter holds a very high value when the guest enables the performance counter. As a result the host's sampling period is configured to be very short. The host then never reconfigures the sampling period and get stuck at entry->PMI->exit loop. We encountered such a scenario in our experiments. The solution is to reprogram the counter even if the guest does not use PMI. Signed-off-by: Nadav Amit Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/pmu.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'arch/x86/kvm/pmu.c') diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index 5c4f631..cbecaa9 100644 --- a/arch/x86/kvm/pmu.c +++ b/arch/x86/kvm/pmu.c @@ -108,7 +108,10 @@ static void kvm_perf_overflow(struct perf_event *perf_event, { struct kvm_pmc *pmc = perf_event->overflow_handler_context; struct kvm_pmu *pmu = &pmc->vcpu->arch.pmu; - __set_bit(pmc->idx, (unsigned long *)&pmu->global_status); + if (!test_and_set_bit(pmc->idx, (unsigned long *)&pmu->reprogram_pmi)) { + __set_bit(pmc->idx, (unsigned long *)&pmu->global_status); + kvm_make_request(KVM_REQ_PMU, pmc->vcpu); + } } static void kvm_perf_overflow_intr(struct perf_event *perf_event, @@ -117,7 +120,7 @@ static void kvm_perf_overflow_intr(struct perf_event *perf_event, struct kvm_pmc *pmc = perf_event->overflow_handler_context; struct kvm_pmu *pmu = &pmc->vcpu->arch.pmu; if (!test_and_set_bit(pmc->idx, (unsigned long *)&pmu->reprogram_pmi)) { - kvm_perf_overflow(perf_event, data, regs); + __set_bit(pmc->idx, (unsigned long *)&pmu->global_status); kvm_make_request(KVM_REQ_PMU, pmc->vcpu); /* * Inject PMI. If vcpu was in a guest mode during NMI PMI -- cgit v1.1