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authorThomas Gleixner <tglx@linutronix.de>2007-03-24 23:02:49 +0100
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-03-24 15:45:53 -0700
commitd9a5c0a4e0b4c84850a1a5bbacba3f7858b67037 (patch)
tree5efaefd34302050ef6d530dafc20635c7ad2842b
parent8fb303c7f1118b0a82aa08e33429adf9b5ad192c (diff)
downloadlinux-2.6.34-ux500-d9a5c0a4e0b4c84850a1a5bbacba3f7858b67037.tar.gz
[PATCH] i386: Prevent early access to TSC to avoid crash on TSCless systems
commit f9690982b8c2f9a2c65acdc113e758ec356676a3 removed the check for cpu_khz from sched_clock(), which prevented early access to the TSC by non obvious magic. This is harmless as long as the CPU has a TSC. On TSCless systems this results in an illegal instruction trap. Replace tsc_disabled and tsc_unstable by tsc_enabled, which is only set when the tsc is available and not unstable. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--arch/i386/kernel/tsc.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index 0e65f7ab63a..6cb8f533673 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -18,6 +18,8 @@
#include "mach_timer.h"
+static int tsc_enabled;
+
/*
* On some systems the TSC frequency does not
* change with the cpu frequency. So we need
@@ -105,7 +107,7 @@ unsigned long long sched_clock(void)
/*
* Fall back to jiffies if there's no TSC available:
*/
- if (tsc_unstable || unlikely(tsc_disable))
+ if (unlikely(!tsc_enabled))
/* No locking but a rare wrong value is not a big deal: */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
@@ -283,6 +285,7 @@ void mark_tsc_unstable(void)
{
if (!tsc_unstable) {
tsc_unstable = 1;
+ tsc_enabled = 0;
/* Can be called before registration */
if (clocksource_tsc.mult)
clocksource_change_rating(&clocksource_tsc, 0);
@@ -383,7 +386,9 @@ 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);
return;