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timekeeping: Prepare timekeeping_cycles_to_ns() for overflow safety

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

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240325064023.2997-17-adrian.hunter@intel.com
This commit is contained in:
Adrian Hunter 2024-03-25 08:40:20 +02:00 committed by Thomas Gleixner
parent 3094c6db1c
commit e809a80aa0
1 changed files with 11 additions and 1 deletions
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12
kernel/time/timekeeping.c
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@ -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;
}