From d9a5c0a4e0b4c84850a1a5bbacba3f7858b67037 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 24 Mar 2007 23:02:49 +0100 Subject: [PATCH] [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 Acked-by: Ingo Molnar Signed-off-by: Linus Torvalds --- arch/i386/kernel/tsc.c | 9 +++++++-- 1 file 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; -- 2.20.1