intel_idle: Fix intel_idle() vs tracing

cpuidle->enter() callbacks should not call into tracing because RCU
has already been disabled. Instead of doing the broadcast thing
itself, simply advertise to the cpuidle core that those states stop
the timer.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lkml.kernel.org/r/20201123143510.GR3021@hirez.programming.kicks-ass.net

drivers/idle/intel_idle.c

@@ -126,26 +126,9 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
 	struct cpuidle_state *state = &drv->states[index];
 	unsigned long eax = flg2MWAIT(state->flags);
 	unsigned long ecx = 1; /* break on interrupt flag */
-	bool tick;
-
-	if (!static_cpu_has(X86_FEATURE_ARAT)) {
-		/*
-		 * Switch over to one-shot tick broadcast if the target C-state
-		 * is deeper than C1.
-		 */
-		if ((eax >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) {
-			tick = true;
-			tick_broadcast_enter();
-		} else {
-			tick = false;
-		}
-	}
 
 	mwait_idle_with_hints(eax, ecx);
 
-	if (!static_cpu_has(X86_FEATURE_ARAT) && tick)
-		tick_broadcast_exit();
-
 	return index;
 }
 
@@ -1227,6 +1210,20 @@ static bool __init intel_idle_acpi_cst_extract(void)
 	return false;
 }
 
+static bool __init intel_idle_state_needs_timer_stop(struct cpuidle_state *state)
+{
+	unsigned long eax = flg2MWAIT(state->flags);
+
+	if (boot_cpu_has(X86_FEATURE_ARAT))
+		return false;
+
+	/*
+	 * Switch over to one-shot tick broadcast if the target C-state
+	 * is deeper than C1.
+	 */
+	return !!((eax >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK);
+}
+
 static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
 {
 	int cstate, limit = min_t(int, CPUIDLE_STATE_MAX, acpi_state_table.count);
@@ -1269,6 +1266,9 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
 		if (disabled_states_mask & BIT(cstate))
 			state->flags |= CPUIDLE_FLAG_OFF;
 
+		if (intel_idle_state_needs_timer_stop(state))
+			state->flags |= CPUIDLE_FLAG_TIMER_STOP;
+
 		state->enter = intel_idle;
 		state->enter_s2idle = intel_idle_s2idle;
 	}
@@ -1507,6 +1507,9 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 		     !(cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_ALWAYS_ENABLE)))
 			drv->states[drv->state_count].flags |= CPUIDLE_FLAG_OFF;
 
+		if (intel_idle_state_needs_timer_stop(&drv->states[drv->state_count]))
+			drv->states[drv->state_count].flags |= CPUIDLE_FLAG_TIMER_STOP;
+
 		drv->state_count++;
 	}