Commit c163e40a authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

timekeeping: Always check for negative motion 



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 135225a3 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: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarJohn Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20241031120328.599430157@linutronix.de
parent d44d2698

arch/x86/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -145,7 +145,6 @@ config X86 
	select ARCH_HAS_PARANOID_L1D_FLUSH

	select BUILDTIME_TABLE_SORT

	select CLKEVT_I8253

	select CLOCKSOURCE_VALIDATE_LAST_CYCLE

	select CLOCKSOURCE_WATCHDOG

	# Word-size accesses may read uninitialized data past the trailing \0

	# in strings and cause false KMSAN reports.

kernel/time/Kconfig

+0 −5
Original line number Diff line number Diff line
@@ -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

kernel/time/timekeeping_internal.h

+0 −7
Original line number Diff line number Diff line
@@ -30,7 +30,6 @@ static inline void timekeeping_inc_mg_floor_swaps(void) 


#endif



#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE

static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)

{

	u64 ret = (now - last) & mask;
@@ -41,12 +40,6 @@ 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



/* Semi public for serialization of non timekeeper VDSO updates. */

unsigned long timekeeper_lock_irqsave(void);