[PATCH] x86-64: Avoid overflows during apic timer calibration

- Use 64bit TSC calculations to avoid handling overflow
- Use 32bit unsigned arithmetic for the APIC timer. This
way overflows are handled correctly.
- Fix exit check of loop to account for apic timer counting down

Signed-off-by: dpreed@reed.com
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 6 insertions, 5 deletions

diff --git a/arch/x86_64/kernel/apic.c b/arch/x86_64/kernel/apic.c
index 943ec4d1bd8e..d198f7d82e5a 100644
--- a/arch/x86_64/kernel/apic.c
+++ b/arch/x86_64/kernel/apic.c
@@ -839,14 +839,15 @@ static void setup_APIC_timer(unsigned int clocks)
 
 static int __init calibrate_APIC_clock(void)
 {
-        int apic, apic_start, tsc, tsc_start;
+        unsigned apic, apic_start;
+        unsigned long tsc, tsc_start;
         int result;
         /*
          * Put whatever arbitrary (but long enough) timeout
          * value into the APIC clock, we just want to get the
          * counter running for calibration.
          */
-        __setup_APIC_LVTT(1000000000);
+        __setup_APIC_LVTT(4000000000);
 
         apic_start = apic_read(APIC_TMCCT);
 #ifdef CONFIG_X86_PM_TIMER
@@ -857,13 +858,13 @@ static int __init calibrate_APIC_clock(void)
         } else
 #endif
         {
-                rdtscl(tsc_start);
+                rdtscll(tsc_start);
 
                 do {
                         apic = apic_read(APIC_TMCCT);
-                        rdtscl(tsc);
+                        rdtscll(tsc);
                 } while ((tsc - tsc_start) < TICK_COUNT &&
-                                (apic - apic_start) < TICK_COUNT);
+                                (apic_start - apic) < TICK_COUNT);
 
                 result = (apic_start - apic) * 1000L * tsc_khz /
                                         (tsc - tsc_start);