powerpc: Fix a lazy irq related WARING in arch_local_irq_restore()

The pseries CPU hotplug code uses cede_processor without properly
synchronizing the SW and HW interrupt enable state. This fixes
it using the same helpers that were written for the idle code.

Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>

=======================
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/hotplug-cpu.c

@@ -127,16 +127,24 @@ static void pseries_mach_cpu_die(void)
 			get_lppaca()->donate_dedicated_cpu = 1;
 
 		while (get_preferred_offline_state(cpu) == CPU_STATE_INACTIVE) {
+			while (!prep_irq_for_idle()) {
+				local_irq_enable();
+				local_irq_disable();
+			}
+
 			extended_cede_processor(cede_latency_hint);
 		}
 
+		local_irq_disable();
+
 		if (!get_lppaca()->shared_proc)
 			get_lppaca()->donate_dedicated_cpu = 0;
 		get_lppaca()->idle = 0;
 
 		if (get_preferred_offline_state(cpu) == CPU_STATE_ONLINE) {
 			unregister_slb_shadow(hwcpu);
 
+			hard_irq_disable();
 			/*
 			 * Call to start_secondary_resume() will not return.
 			 * Kernel stack will be reset and start_secondary()

arch/powerpc/platforms/pseries/plpar_wrappers.h

@@ -2,6 +2,7 @@
 #define _PSERIES_PLPAR_WRAPPERS_H
 
 #include <linux/string.h>
+#include <linux/irqflags.h>
 
 #include <asm/hvcall.h>
 #include <asm/paca.h>
@@ -41,7 +42,14 @@ static inline long extended_cede_processor(unsigned long latency_hint)
 	u8 old_latency_hint = get_cede_latency_hint();
 
 	set_cede_latency_hint(latency_hint);
+
 	rc = cede_processor();
+#ifdef CONFIG_TRACE_IRQFLAGS
+		/* Ensure that H_CEDE returns with IRQs on */
+		if (WARN_ON(!(mfmsr() & MSR_EE)))
+			__hard_irq_enable();
+#endif
+
 	set_cede_latency_hint(old_latency_hint);
 
 	return rc;