1 files changed, 13 insertions, 10 deletions

diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
index e4790728b224..65b70637ad97 100644
--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -14,7 +14,10 @@
 
 #include "mach_timer.h"
 
-static int tsc_enabled;
+/* native_sched_clock() is called before tsc_init(), so
+   we must start with the TSC soft disabled to prevent
+   erroneous rdtsc usage on !cpu_has_tsc processors */
+static int tsc_disabled = -1;
 
 /*
  * On some systems the TSC frequency does not
@@ -28,8 +31,8 @@ EXPORT_SYMBOL_GPL(tsc_khz);
 static int __init tsc_setup(char *str)
 {
         printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
-                                "cannot disable TSC completely.\n");
-        mark_tsc_unstable("user disabled TSC");
+               "cannot disable TSC completely.\n");
+        tsc_disabled = 1;
         return 1;
 }
 #else
@@ -120,7 +123,7 @@ unsigned long long native_sched_clock(void)
          *   very important for it to be as fast as the platform
          *   can achive it. )
          */
-        if (unlikely(!tsc_enabled && !tsc_unstable))
+        if (unlikely(tsc_disabled))
                 /* No locking but a rare wrong value is not a big deal: */
                 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 
@@ -322,7 +325,6 @@ void mark_tsc_unstable(char *reason)
 {
         if (!tsc_unstable) {
                 tsc_unstable = 1;
-                tsc_enabled = 0;
                 printk("Marking TSC unstable due to: %s.\n", reason);
                 /* Can be called before registration */
                 if (clocksource_tsc.mult)
@@ -336,7 +338,7 @@ EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 static int __init dmi_mark_tsc_unstable(const struct dmi_system_id *d)
 {
         printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
-                       d->ident);
+               d->ident);
         tsc_unstable = 1;
         return 0;
 }
@@ -403,7 +405,7 @@ void __init tsc_init(void)
 {
         int cpu;
 
-        if (!cpu_has_tsc)
+        if (!cpu_has_tsc || tsc_disabled > 0)
                 return;
 
         cpu_khz = calculate_cpu_khz();
@@ -414,6 +416,9 @@ void __init tsc_init(void)
                 return;
         }
 
+        /* now allow native_sched_clock() to use rdtsc */
+        tsc_disabled = 0;
+
         printk("Detected %lu.%03lu MHz processor.\n",
                                 (unsigned long)cpu_khz / 1000,
                                 (unsigned long)cpu_khz % 1000);
@@ -441,8 +446,6 @@ void __init tsc_init(void)
         if (check_tsc_unstable()) {
                 clocksource_tsc.rating = 0;
                 clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
-        } else
-                tsc_enabled = 1;
-
+        }
         clocksource_register(&clocksource_tsc);
 }