x86: voluntary leave_mm before entering ACPI C3

Aviod TLB flush IPIs during C3 states by voluntary leave_mm()
before entering C3.

The performance impact of TLB flush on C3 should not be significant with
respect to C3 wakeup latency. Also, CPUs tend to flush TLB in hardware while in
C3 anyways.

On a 8 logical CPU system, running make -j2, the number of tlbflush IPIs goes
down from 40 per second to ~ 0. Total number of interrupts during the run
of this workload was ~1200 per second, which makes it ~3% savings in wakeups.

There was no measurable performance or power impact however.

[ akpm@linux-foundation.org: symbol export fixes. ]

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/acpi/processor_idle.c

@@ -534,6 +534,7 @@ static void acpi_processor_idle(void)
 		break;
 
 	case ACPI_STATE_C3:
+		acpi_unlazy_tlb(smp_processor_id());
 		/*
 		 * Must be done before busmaster disable as we might
 		 * need to access HPET !
@@ -1423,6 +1424,7 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
 		return 0;
 	}
 
+	acpi_unlazy_tlb(smp_processor_id());
 	/*
 	 * Must be done before busmaster disable as we might need to
 	 * access HPET !