forked from Minki/linux
KVM: x86: never specify a sample period for virtualized in_tx_cp counters
pmc_reprogram_counter() always sets a sample period based on the value of pmc->counter. However, hsw_hw_config() rejects sample periods less than 2^31 - 1. So for example, if a KVM guest does struct perf_event_attr attr; memset(&attr, 0, sizeof(attr)); attr.type = PERF_TYPE_RAW; attr.size = sizeof(attr); attr.config = 0x2005101c4; // conditional branches retired IN_TXCP attr.sample_period = 0; int fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0); ioctl(fd, PERF_EVENT_IOC_DISABLE, 0); ioctl(fd, PERF_EVENT_IOC_ENABLE, 0); the guest kernel counts some conditional branch events, then updates the virtual PMU register with a nonzero count. The host reaches pmc_reprogram_counter() with nonzero pmc->counter, triggers EOPNOTSUPP in hsw_hw_config(), prints "kvm_pmu: event creation failed" in pmc_reprogram_counter(), and silently (from the guest's point of view) stops counting events. We fix event counting by forcing attr.sample_period to always be zero for in_tx_cp counters. Sampling doesn't work, but it already didn't work and can't be fixed without major changes to the approach in hsw_hw_config(). Signed-off-by: Robert O'Callahan <robert@ocallahan.org> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
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@ -113,12 +113,19 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
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.config = config,
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};
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attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc);
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if (in_tx)
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attr.config |= HSW_IN_TX;
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if (in_tx_cp)
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if (in_tx_cp) {
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/*
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* HSW_IN_TX_CHECKPOINTED is not supported with nonzero
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* period. Just clear the sample period so at least
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* allocating the counter doesn't fail.
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*/
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attr.sample_period = 0;
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attr.config |= HSW_IN_TX_CHECKPOINTED;
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attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc);
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}
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event = perf_event_create_kernel_counter(&attr, -1, current,
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intr ? kvm_perf_overflow_intr :
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