3 files changed, 29 insertions, 3 deletions

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 7402c818..5e830d0 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -597,6 +597,19 @@ void x86_pmu_disable_all(void)
 	}
 }
 
+/*
+ * There may be PMI landing after enabled=0. The PMI hitting could be before or
+ * after disable_all.
+ *
+ * If PMI hits before disable_all, the PMU will be disabled in the NMI handler.
+ * It will not be re-enabled in the NMI handler again, because enabled=0. After
+ * handling the NMI, disable_all will be called, which will not change the
+ * state either. If PMI hits after disable_all, the PMU is already disabled
+ * before entering NMI handler. The NMI handler will not change the state
+ * either.
+ *
+ * So either situation is harmless.
+ */
 static void x86_pmu_disable(struct pmu *pmu)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index a7ec685..b3f6349 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -1502,7 +1502,15 @@ static __initconst const u64 knl_hw_cache_extra_regs
 };
 
 /*
- * Use from PMIs where the LBRs are already disabled.
+ * Used from PMIs where the LBRs are already disabled.
+ *
+ * This function could be called consecutively. It is required to remain in
+ * disabled state if called consecutively.
+ *
+ * During consecutive calls, the same disable value will be written to related
+ * registers, so the PMU state remains unchanged. hw.state in
+ * intel_bts_disable_local will remain PERF_HES_STOPPED too in consecutive
+ * calls.
  */
 static void __intel_pmu_disable_all(void)
 {
@@ -1929,7 +1937,10 @@ again:
 		goto again;
 
 done:
-	__intel_pmu_enable_all(0, true);
+	/* Only restore PMU state when it's active. See x86_pmu_disable(). */
+	if (cpuc->enabled)
+		__intel_pmu_enable_all(0, true);
+
 	/*
 	 * Only unmask the NMI after the overflow counters
 	 * have been reset. This avoids spurious NMIs on
diff --git a/arch/x86/events/intel/knc.c b/arch/x86/events/intel/knc.c
index 206226e..548d5f7 100644
--- a/arch/x86/events/intel/knc.c
+++ b/arch/x86/events/intel/knc.c
@@ -263,7 +263,9 @@ again:
 		goto again;
 
 done:
-	knc_pmu_enable_all(0);
+	/* Only restore PMU state when it's active. See x86_pmu_disable(). */
+	if (cpuc->enabled)
+		knc_pmu_enable_all(0);
 
 	return handled;
 }