* [PATCH] KVM: x86: never specify a sample period for virtualized in_tx_cp counters
@ 2017-01-31 1:48 Robert O'Callahan
2017-01-31 7:34 ` Ingo Molnar
0 siblings, 1 reply; 2+ messages in thread
From: Robert O'Callahan @ 2017-01-31 1:48 UTC (permalink / raw)
To: kvm
Cc: Paolo Bonzini, Radim Krčmář,
Thomas Gleixner, Ingo Molnar, H . Peter Anvin, x86, linux-kernel,
Robert O'Callahan
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, a KVM guest doing
perf stat -e r2005101c4 sleep 0
will count some conditional branch events, deschedule the task, reschedule
the task, try to restore the guest PMU state for the task, in the host
reach pmc_reprogram_counter() with nonzero pmc->count, trigger EOPNOTSUPP
in hsw_hw_config(), print "kvm_pmu: event creation failed" in
pmc_reprogram_counter(), and silently (from the guest's point of view) stop
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>
---
arch/x86/kvm/pmu.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 06ce377..af993d7 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -113,12 +113,18 @@ 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 :
--
2.9.3
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] KVM: x86: never specify a sample period for virtualized in_tx_cp counters
2017-01-31 1:48 [PATCH] KVM: x86: never specify a sample period for virtualized in_tx_cp counters Robert O'Callahan
@ 2017-01-31 7:34 ` Ingo Molnar
0 siblings, 0 replies; 2+ messages in thread
From: Ingo Molnar @ 2017-01-31 7:34 UTC (permalink / raw)
To: Robert O'Callahan
Cc: kvm, Paolo Bonzini, Radim Krčmář,
Thomas Gleixner, Ingo Molnar, H . Peter Anvin, x86, linux-kernel
* Robert O'Callahan <robert@ocallahan.org> wrote:
> 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, a KVM guest doing
> perf stat -e r2005101c4 sleep 0
> will count some conditional branch events, deschedule the task, reschedule
> the task, try to restore the guest PMU state for the task, in the host
> reach pmc_reprogram_counter() with nonzero pmc->count, trigger EOPNOTSUPP
> in hsw_hw_config(), print "kvm_pmu: event creation failed" in
> pmc_reprogram_counter(), and silently (from the guest's point of view) stop
> 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>
> ---
> arch/x86/kvm/pmu.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 06ce377..af993d7 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -113,12 +113,18 @@ 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);
> + }
please use the customary (multi-line) comment style:
/*
* Comment .....
* ...... goes here.
*/
specified in Documentation/CodingStyle.
Thanks,
Ingo
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