Open code clocksource_delta() in timekeeping_cycles_to_ns() so that
overflow safety can be added efficiently.
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
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
