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 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@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20241031120328.599430157@linutronix.de

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2852fcd82cbd8c48983c92f0b6634a1c475b9404..53a5eda8219c2e7dbddfda42856601904387fb6c 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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.

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 8ebb6d5a106bea9ed6f9f23faadbdae7358cf036..b0b97a60aaa6fc21c93005ef393d56afbac7fa5c 100644 (file)
--- 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 b3dca834f48ca85f6e7bbd355ab63921ebe3bb41..63e600e943a767cd60aa306966687be44c335b1e 100644 (file)
--- a/kernel/time/timekeeping_internal.h
+++ b/kernel/time/timekeeping_internal.h
@@ -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);