This is a note to let you know that I've just added the patch titled
timekeeping: Always check for negative motion
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
timekeeping-always-check-for-negative-motion.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a6188d33b7a5ea1f492ad8a52645e5698698ba38
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Thu Oct 31 13:04:08 2024 +0100
timekeeping: Always check for negative motion
[ Upstream commit c163e40af9b2331b2c629fd4ec8b703ed4d4ae39 ]
clocksource_delta() has two variants. One with a check for negative motion,
which is only selected by x86. This is a historic leftover as this function
was previously used in the time getter hot paths.
Since 135225a363ae timekeeping_cycles_to_ns() has unconditional protection
against this as a by-product of the protection against 64bit math overflow.
clocksource_delta() is only used in the clocksource watchdog and in
timekeeping_advance(). The extra conditional there is not hurting anyone.
Remove the config option and unconditionally prevent negative motion of the
readout.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: John Stultz <jstultz@xxxxxxxxxx>
Link: https://lore.kernel.org/all/20241031120328.599430157@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index df0a3a1b08ae0..a3e7f75a8cfa8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -99,7 +99,6 @@ config X86
select ARCH_WANTS_THP_SWAP if X86_64
select BUILDTIME_EXTABLE_SORT
select CLKEVT_I8253
- select CLOCKSOURCE_VALIDATE_LAST_CYCLE
select CLOCKSOURCE_WATCHDOG
select DCACHE_WORD_ACCESS
select EDAC_ATOMIC_SCRUB
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index fcc42353f1253..4b9a8653a6327 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -17,11 +17,6 @@ config ARCH_CLOCKSOURCE_DATA
config ARCH_CLOCKSOURCE_INIT
bool
-# Clocksources require validation of the clocksource against the last
-# cycle update - x86/TSC misfeature
-config CLOCKSOURCE_VALIDATE_LAST_CYCLE
- bool
-
# Timekeeping vsyscall support
config GENERIC_TIME_VSYSCALL
bool
diff --git a/kernel/time/timekeeping_internal.h b/kernel/time/timekeeping_internal.h
index bcbb52db22565..d7f99e69bce4b 100644
--- a/kernel/time/timekeeping_internal.h
+++ b/kernel/time/timekeeping_internal.h
@@ -13,7 +13,6 @@ extern void tk_debug_account_sleep_time(const struct timespec64 *t);
#define tk_debug_account_sleep_time(x)
#endif
-#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE
static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)
{
u64 ret = (now - last) & mask;
@@ -24,11 +23,5 @@ static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)
*/
return ret & ~(mask >> 1) ? 0 : ret;
}
-#else
-static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)
-{
- return (now - last) & mask;
-}
-#endif
#endif /* _TIMEKEEPING_INTERNAL_H */
