Commit e809a80a authored by Adrian Hunter's avatar Adrian Hunter Committed by Thomas Gleixner
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timekeeping: Prepare timekeeping_cycles_to_ns() for overflow safety 



Open code clocksource_delta() in timekeeping_cycles_to_ns() so that
overflow safety can be added efficiently.

Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAdrian Hunter <adrian.hunter@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240325064023.2997-17-adrian.hunter@intel.com
parent 3094c6db

kernel/time/timekeeping.c

+11 −1
Original line number Diff line number Diff line
@@ -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;

}