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Commit d9a5c0a4 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Linus Torvalds
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[PATCH] i386: Prevent early access to TSC to avoid crash on TSCless systems 



commit f9690982 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: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8fb303c7

arch/i386/kernel/tsc.c

+7 −2
Original line number Diff line number Diff line
@@ -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;