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| author | Robert O'Callahan <robert@ocallahan.org> | 2017-02-01 05:06:11 +0100 |
|---|---|---|
| committer | Radim Krčmář <rkrcmar@redhat.com> | 2017-03-01 14:19:46 +0100 |
| commit | bba82fd75694832b59433bf4e9d7ede8de1dfd42 (patch) | |
| tree | caa0c64d07c5f5178ad0c102888fb49bc81930fa | |
| parent | Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm (diff) | |
| download | linux-bba82fd75694832b59433bf4e9d7ede8de1dfd42.tar.xz linux-bba82fd75694832b59433bf4e9d7ede8de1dfd42.zip | |
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>
| -rw-r--r-- | arch/x86/kvm/pmu.c | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index 06ce377dcbc9..026db42a86c3 100644 --- a/arch/x86/kvm/pmu.c +++ b/arch/x86/kvm/pmu.c @@ -113,12 +113,19 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type, .config = config, }; + attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc); + if (in_tx) attr.config |= HSW_IN_TX; - if (in_tx_cp) + if (in_tx_cp) { + /* + * HSW_IN_TX_CHECKPOINTED is not supported with nonzero + * period. Just clear the sample period so at least + * allocating the counter doesn't fail. + */ + attr.sample_period = 0; attr.config |= HSW_IN_TX_CHECKPOINTED; - - attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc); + } event = perf_event_create_kernel_counter(&attr, -1, current, intr ? kvm_perf_overflow_intr : |