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authorThomas Gleixner <tglx@linutronix.de>2014-07-17 01:05:12 +0400
committerJohn Stultz <john.stultz@linaro.org>2014-07-24 02:01:51 +0400
commit09ec54429c6d10f87d1f084de53ae2c1c3a81108 (patch)
tree842749293edd755e8bb12e1433c2f9df7dd842cf /kernel/time
parent3a97837784acbf9fed699fc04d1799b0eb742fdf (diff)
downloadlinux-09ec54429c6d10f87d1f084de53ae2c1c3a81108.tar.xz
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 <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/Kconfig5
-rw-r--r--kernel/time/timekeeping_internal.h9
2 files changed, 14 insertions, 0 deletions
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 */