[PATCH V2 16/19] timekeeping: Prepare timekeeping_cycles_to_ns() for overflow safety
From: Adrian Hunter <adrian.hunter@intel.com>
Date: 2024-03-25 06:42:25
Also in:
linux-s390, lkml
Subsystem:
the rest, timekeeping, clocksource core, ntp, alarmtimer · Maintainers:
Linus Torvalds, John Stultz, Thomas Gleixner
Open code clocksource_delta() in timekeeping_cycles_to_ns() so that overflow safety can be added efficiently. Suggested-by: Thomas Gleixner <redacted> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> --- kernel/time/timekeeping.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 749387f22f0f..d17484082e2c 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c@@ -367,7 +367,17 @@ static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock) static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 cycles) { /* Calculate the delta since the last update_wall_time() */ - u64 delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask); + u64 mask = tkr->mask, delta = (cycles - tkr->cycle_last) & mask; + + if (IS_ENABLED(CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE)) { + /* + * Handle clocksource inconsistency between CPUs to prevent + * time from going backwards by checking for the MSB of the + * mask being set in the delta. + */ + if (unlikely(delta & ~(mask >> 1))) + return tkr->xtime_nsec >> tkr->shift; + } return ((delta * tkr->mult) + tkr->xtime_nsec) >> tkr->shift; }
--
2.34.1