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Subject[PATCH 2/4] KVM: x86/pmu: Clear "reprogram" bit if counter is disabled or disallowed
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When reprogramming a counter, clear the counter's "reprogram pending" bit
if the counter is disabled (by the guest) or is disallowed (by the
userspace filter). In both cases, there's no need to re-attempt
programming on the next coincident KVM_REQ_PMU as enabling the counter by
either method will trigger reprogramming.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/pmu.c | 38 ++++++++++++++++++++++++--------------
1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 4504987cbbe2..4cd99320019b 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -150,9 +150,9 @@ static void kvm_perf_overflow(struct perf_event *perf_event,
__kvm_perf_overflow(pmc, true);
}

-static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
- u64 config, bool exclude_user,
- bool exclude_kernel, bool intr)
+static int pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type, u64 config,
+ bool exclude_user, bool exclude_kernel,
+ bool intr)
{
struct kvm_pmu *pmu = pmc_to_pmu(pmc);
struct perf_event *event;
@@ -204,14 +204,14 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
if (IS_ERR(event)) {
pr_debug_ratelimited("kvm_pmu: event creation failed %ld for pmc->idx = %d\n",
PTR_ERR(event), pmc->idx);
- return;
+ return PTR_ERR(event);
}

pmc->perf_event = event;
pmc_to_pmu(pmc)->event_count++;
- clear_bit(pmc->idx, pmc_to_pmu(pmc)->reprogram_pmi);
pmc->is_paused = false;
pmc->intr = intr || pebs;
+ return 0;
}

static void pmc_pause_counter(struct kvm_pmc *pmc)
@@ -245,7 +245,6 @@ static bool pmc_resume_counter(struct kvm_pmc *pmc)
perf_event_enable(pmc->perf_event);
pmc->is_paused = false;

- clear_bit(pmc->idx, (unsigned long *)&pmc_to_pmu(pmc)->reprogram_pmi);
return true;
}

@@ -303,10 +302,10 @@ void reprogram_counter(struct kvm_pmc *pmc)
pmc_pause_counter(pmc);

if (!pmc_speculative_in_use(pmc) || !pmc_is_enabled(pmc))
- return;
+ goto reprogram_complete;

if (!check_pmu_event_filter(pmc))
- return;
+ goto reprogram_complete;

if (eventsel & ARCH_PERFMON_EVENTSEL_PIN_CONTROL)
printk_once("kvm pmu: pin control bit is ignored\n");
@@ -324,16 +323,27 @@ void reprogram_counter(struct kvm_pmc *pmc)
}

if (pmc->current_config == new_config && pmc_resume_counter(pmc))
- return;
+ goto reprogram_complete;

pmc_release_perf_event(pmc);

pmc->current_config = new_config;
- pmc_reprogram_counter(pmc, PERF_TYPE_RAW,
- (eventsel & pmu->raw_event_mask),
- !(eventsel & ARCH_PERFMON_EVENTSEL_USR),
- !(eventsel & ARCH_PERFMON_EVENTSEL_OS),
- eventsel & ARCH_PERFMON_EVENTSEL_INT);
+
+ /*
+ * If reprogramming fails, e.g. due to contention, leave the counter's
+ * regprogram bit set, i.e. opportunistically try again on the next PMU
+ * refresh. Don't make a new request as doing so can stall the guest
+ * if reprogramming repeatedly fails.
+ */
+ if (pmc_reprogram_counter(pmc, PERF_TYPE_RAW,
+ (eventsel & pmu->raw_event_mask),
+ !(eventsel & ARCH_PERFMON_EVENTSEL_USR),
+ !(eventsel & ARCH_PERFMON_EVENTSEL_OS),
+ eventsel & ARCH_PERFMON_EVENTSEL_INT))
+ return;
+
+reprogram_complete:
+ clear_bit(pmc->idx, (unsigned long *)&pmc_to_pmu(pmc)->reprogram_pmi);
}
EXPORT_SYMBOL_GPL(reprogram_counter);

--
2.37.3.998.g577e59143f-goog
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