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, 8 insertions, 3 deletions

diff --git a/arch/x86/kernel/apic_32.c b/arch/x86/kernel/apic_32.c
index d07a603807d1..35a568ea8400 100644
--- a/arch/x86/kernel/apic_32.c
+++ b/arch/x86/kernel/apic_32.c
@@ -99,6 +99,8 @@ static DEFINE_PER_CPU(struct clock_event_device, lapic_events);
 /* Local APIC was disabled by the BIOS and enabled by the kernel */
 static int enabled_via_apicbase;
 
+static unsigned long apic_phys;
+
 /*
  * Get the LAPIC version
  */
@@ -631,9 +633,14 @@ int setup_profiling_timer(unsigned int multiplier)
  */
 void clear_local_APIC(void)
 {
-        int maxlvt = lapic_get_maxlvt();
+        int 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.
@@ -1120,8 +1127,6 @@ no_apic:
  */
 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