2024-03-25 13:06:37

by Adrian Hunter

Subject: [PATCH V2 16/19] 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: Thomas Gleixner <[email protected]>
Signed-off-by: Adrian Hunter <[email protected]>
---
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

2024-04-08 13:11:16

by tip-bot2 for Tony Luck

Subject: [tip: timers/core] timekeeping: Prepare timekeeping_cycles_to_ns() for overflow safety

The following commit has been merged into the timers/core branch of tip:

Commit-ID: e809a80aa0bcf802f99407c23fd6be6fd4eb250a
Gitweb: https://git.kernel.org/tip/e809a80aa0bcf802f99407c23fd6be6fd4eb250a
Author: Adrian Hunter <[email protected]>
AuthorDate: Mon, 25 Mar 2024 08:40:20 +02:00
Committer: Thomas Gleixner <[email protected]>
CommitterDate: Mon, 08 Apr 2024 15:03:08 +02:00

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: Thomas Gleixner <[email protected]>
Signed-off-by: Adrian Hunter <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

---
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 749387f..d174840 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;
}