x86: don't disable the APIC if it hasn't been mapped yet

When the kernel panics early for some unrelated reason
there would be eventually an early exception inside panic because
clear_local_APIC tried to disable the not yet mapped APIC.
Check for that explicitely.

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

1 files changed, 7 insertions, 2 deletions

diff --git a/arch/x86/kernel/apic_64.c b/arch/x86/kernel/apic_64.c
index 85bd3d463cdf..a7a38c9da136 100644
--- a/arch/x86/kernel/apic_64.c
+++ b/arch/x86/kernel/apic_64.c
@@ -81,6 +81,8 @@ static struct clock_event_device lapic_clockevent = {
 };
 static DEFINE_PER_CPU(struct clock_event_device, lapic_events);
 
+static unsigned long apic_phys;
+
 /*
  * Get the LAPIC version
  */
@@ -525,6 +527,11 @@ void clear_local_APIC(void)
         int maxlvt = lapic_get_maxlvt();
         u32 v;
 
+        /* APIC hasn't been mapped yet */
+        if (!apic_phys)
+                return;
+
+        maxlvt = lapic_get_maxlvt();
         /*
          * Masking an LVT entry can trigger a local APIC error
          * if the vector is zero. Mask LVTERR first to prevent this.
@@ -859,8 +866,6 @@ static int __init detect_init_APIC(void)
  */
 void __init init_apic_mappings(void)
 {
-        unsigned long apic_phys;
-
         /*
          * If no local APIC can be found then set up a fake all
          * zeroes page to simulate the local APIC and another