From 09ec54429c6d10f87d1f084de53ae2c1c3a81108 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 16 Jul 2014 21:05:12 +0000 Subject: clocksource: Move cycle_last validation to core code The only user of the cycle_last validation is the x86 TSC. In order to provide NMI safe accessor functions for clock monotonic and monotonic_raw we need to do that in the core. We can't do the TSC specific if (now < cycle_last) now = cycle_last; for the other wrapping around clocksources, but TSC has CLOCKSOURCE_MASK(64) which actually does not mask out anything so if now is less than cycle_last the subtraction will give a negative result. So we can check for that in clocksource_delta() and return 0 for that case. Implement and enable it for x86 Signed-off-by: Thomas Gleixner Signed-off-by: John Stultz --- kernel/time/Kconfig | 5 +++++ kernel/time/timekeeping_internal.h | 9 +++++++++ 2 files changed, 14 insertions(+) (limited to 'kernel/time') diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index feccfd888732..d626dc98e8df 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -12,6 +12,11 @@ config CLOCKSOURCE_WATCHDOG config ARCH_CLOCKSOURCE_DATA bool +# Clocksources require validation of the clocksource against the last +# cycle update - x86/TSC misfeature +config CLOCKSOURCE_VALIDATE_LAST_CYCLE + bool + # Timekeeping vsyscall support config GENERIC_TIME_VSYSCALL bool diff --git a/kernel/time/timekeeping_internal.h b/kernel/time/timekeeping_internal.h index 05dfa6b25dc4..4ea005a7f9da 100644 --- a/kernel/time/timekeeping_internal.h +++ b/kernel/time/timekeeping_internal.h @@ -12,9 +12,18 @@ extern void tk_debug_account_sleep_time(struct timespec64 *t); #define tk_debug_account_sleep_time(x) #endif +#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE +static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask) +{ + cycle_t ret = (now - last) & mask; + + return (s64) ret > 0 ? ret : 0; +} +#else static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask) { return (now - last) & mask; } +#endif #endif /* _TIMEKEEPING_INTERNAL_H */ -- cgit v1.2.3