perf counters: protect them against CSTATE transitions

Impact: fix rare lost events problem

There are CPUs whose performance counters misbehave on CSTATE transitions,
so provide a way to just disable/enable them around deep idle methods.

(hw_perf_enable_all() is cheap on x86.)

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/perf_counter.c

@@ -12,6 +12,7 @@
 #include <linux/notifier.h>
 #include <linux/hardirq.h>
 #include <linux/kprobes.h>
+#include <linux/module.h>
 #include <linux/kdebug.h>
 #include <linux/sched.h>
 
@@ -119,10 +120,21 @@ void hw_perf_enable_all(void)
 	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, perf_counter_mask, 0);
 }
 
-void hw_perf_disable_all(void)
+void hw_perf_restore_ctrl(u64 ctrl)
 {
+	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, ctrl, 0);
+}
+EXPORT_SYMBOL_GPL(hw_perf_restore_ctrl);
+
+u64 hw_perf_disable_all(void)
+{
+	u64 ctrl;
+
+	rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);
 	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, 0, 0);
+	return ctrl;
 }
+EXPORT_SYMBOL_GPL(hw_perf_disable_all);
 
 static inline void
 __hw_perf_counter_disable(struct hw_perf_counter *hwc, unsigned int idx)

drivers/acpi/processor_idle.c

@@ -270,8 +270,11 @@ static atomic_t c3_cpu_count;
 /* Common C-state entry for C2, C3, .. */
 static void acpi_cstate_enter(struct acpi_processor_cx *cstate)
 {
+	u64 pctrl;
+
 	/* Don't trace irqs off for idle */
 	stop_critical_timings();
+	pctrl = hw_perf_disable_all();
 	if (cstate->entry_method == ACPI_CSTATE_FFH) {
 		/* Call into architectural FFH based C-state */
 		acpi_processor_ffh_cstate_enter(cstate);
@@ -284,6 +287,7 @@ static void acpi_cstate_enter(struct acpi_processor_cx *cstate)
 		   gets asserted in time to freeze execution properly. */
 		unused = inl(acpi_gbl_FADT.xpm_timer_block.address);
 	}
+	hw_perf_restore_ctrl(pctrl);
 	start_critical_timings();
 }
 #endif /* !CONFIG_CPU_IDLE */
@@ -1425,8 +1429,11 @@ static inline void acpi_idle_update_bm_rld(struct acpi_processor *pr,
  */
 static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx)
 {
+	u64 pctrl;
+
 	/* Don't trace irqs off for idle */
 	stop_critical_timings();
+	pctrl = hw_perf_disable_all();
 	if (cx->entry_method == ACPI_CSTATE_FFH) {
 		/* Call into architectural FFH based C-state */
 		acpi_processor_ffh_cstate_enter(cx);
@@ -1441,6 +1448,7 @@ static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx)
 		   gets asserted in time to freeze execution properly. */
 		unused = inl(acpi_gbl_FADT.xpm_timer_block.address);
 	}
+	hw_perf_restore_ctrl(pctrl);
 	start_critical_timings();
 }
 

include/linux/perf_counter.h

@@ -156,6 +156,8 @@ extern void perf_counter_task_tick(struct task_struct *task, int cpu);
 extern void perf_counter_init_task(struct task_struct *task);
 extern void perf_counter_notify(struct pt_regs *regs);
 extern void perf_counter_print_debug(void);
+extern void hw_perf_restore_ctrl(u64 ctrl);
+extern u64 hw_perf_disable_all(void);
 #else
 static inline void
 perf_counter_task_sched_in(struct task_struct *task, int cpu)		{ }
@@ -166,6 +168,8 @@ perf_counter_task_tick(struct task_struct *task, int cpu)		{ }
 static inline void perf_counter_init_task(struct task_struct *task)	{ }
 static inline void perf_counter_notify(struct pt_regs *regs)		{ }
 static inline void perf_counter_print_debug(void)			{ }
+static inline void hw_perf_restore_ctrl(u64 ctrl)			{ }
+static inline u64 hw_perf_disable_all(void)		{ return 0; }
 #endif
 
 #endif /* _LINUX_PERF_COUNTER_H */