KVM: x86/pmu: Add pmc->intr to refactor kvm_perf_overflow{_intr}()

Depending on whether intr should be triggered or not, KVM registers
two different event overflow callbacks in the perf_event context.

The code skeleton of these two functions is very similar, so
the pmc->intr can be stored into pmc from pmc_reprogram_counter()
which provides smaller instructions footprint against the
u-architecture branch predictor.

The __kvm_perf_overflow() can be called in non-nmi contexts
and a flag is needed to distinguish the caller context and thus
avoid a check on kvm_is_in_guest(), otherwise we might get
warnings from suspicious RCU or check_preemption_disabled().
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Like Xu <likexu@tencent.com>
Message-Id: <20211130074221.93635-5-likexu@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -495,6 +495,7 @@ struct kvm_pmc {
 	 */
 	u64 current_config;
 	bool is_paused;
+	bool intr;
 };
 
 struct kvm_pmu {

arch/x86/kvm/pmu.c

@@ -55,30 +55,20 @@ static void kvm_pmi_trigger_fn(struct irq_work *irq_work)
 	kvm_pmu_deliver_pmi(vcpu);
 }
 
-static void kvm_perf_overflow(struct perf_event *perf_event,
-			      struct perf_sample_data *data,
-			      struct pt_regs *regs)
+static inline void __kvm_perf_overflow(struct kvm_pmc *pmc, bool in_pmi)
 {
-	struct kvm_pmc *pmc = perf_event->overflow_handler_context;
 	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
 
-	if (!test_and_set_bit(pmc->idx, 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,
-				   struct perf_sample_data *data,
-				   struct pt_regs *regs)
-{
-	struct kvm_pmc *pmc = perf_event->overflow_handler_context;
-	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
+	/* Ignore counters that have been reprogrammed already. */
+	if (test_and_set_bit(pmc->idx, pmu->reprogram_pmi))
+		return;
 
-	if (!test_and_set_bit(pmc->idx, pmu->reprogram_pmi)) {
 	__set_bit(pmc->idx, (unsigned long *)&pmu->global_status);
 	kvm_make_request(KVM_REQ_PMU, pmc->vcpu);
 
+	if (!pmc->intr)
+		return;
+
 	/*
 	 * Inject PMI. If vcpu was in a guest mode during NMI PMI
 	 * can be ejected on a guest mode re-entry. Otherwise we can't
@@ -87,11 +77,19 @@ static void kvm_perf_overflow_intr(struct perf_event *perf_event,
 	 * woken up. So we should wake it, but this is impossible from
 	 * NMI context. Do it from irq work instead.
 	 */
-		if (!kvm_is_in_guest())
+	if (in_pmi && !kvm_is_in_guest())
 		irq_work_queue(&pmc_to_pmu(pmc)->irq_work);
 	else
 		kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
-	}
+}
+
+static void kvm_perf_overflow(struct perf_event *perf_event,
+			      struct perf_sample_data *data,
+			      struct pt_regs *regs)
+{
+	struct kvm_pmc *pmc = perf_event->overflow_handler_context;
+
+	__kvm_perf_overflow(pmc, true);
 }
 
 static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
@@ -126,7 +124,6 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
 	}
 
 	event = perf_event_create_kernel_counter(&attr, -1, current,
-						 intr ? kvm_perf_overflow_intr :
 						 kvm_perf_overflow, pmc);
 	if (IS_ERR(event)) {
 		pr_debug_ratelimited("kvm_pmu: event creation failed %ld for pmc->idx = %d\n",
@@ -138,6 +135,7 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
 	pmc_to_pmu(pmc)->event_count++;
 	clear_bit(pmc->idx, pmc_to_pmu(pmc)->reprogram_pmi);
 	pmc->is_paused = false;
+	pmc->intr = intr;
 }
 
 static void pmc_pause_counter(struct kvm_pmc *pmc)