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[PATCH] i386: Prevent early access to TSC to avoid crash on TSCless systems 

commit f9690982b8 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>
This commit is contained in:
Thomas Gleixner 2007-03-24 23:02:49 +01:00 committed by Linus Torvalds
parent 8fb303c7f1
commit d9a5c0a4e0
1 changed files with 7 additions and 2 deletions
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9
arch/i386/kernel/tsc.c
View File

@ -18,6 +18,8 @@
#include "mach_timer.h" #include "mach_timer.h"
static int tsc_enabled;
/* /*
* On some systems the TSC frequency does not * On some systems the TSC frequency does not
* change with the cpu frequency. So we need * 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: * 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: */ /* No locking but a rare wrong value is not a big deal: */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ); return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
@ -283,6 +285,7 @@ void mark_tsc_unstable(void)
{ {
if (!tsc_unstable) { if (!tsc_unstable) {
tsc_unstable = 1; tsc_unstable = 1;
tsc_enabled = 0;
/* Can be called before registration */ /* Can be called before registration */
if (clocksource_tsc.mult) if (clocksource_tsc.mult)
clocksource_change_rating(&clocksource_tsc, 0); clocksource_change_rating(&clocksource_tsc, 0);
@ -383,7 +386,9 @@ void __init tsc_init(void)
if (check_tsc_unstable()) { if (check_tsc_unstable()) {
clocksource_tsc.rating = 0; clocksource_tsc.rating = 0;
clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS; clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
} } else
tsc_enabled = 1;
clocksource_register(&clocksource_tsc); clocksource_register(&clocksource_tsc);
return; return;