4 files changed, 24 insertions, 12 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7fa17b5ce668..d08e061c187a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -109,6 +109,7 @@ config X86
         select CLOCKSOURCE_WATCHDOG
         select GENERIC_CLOCKEVENTS
         select ARCH_CLOCKSOURCE_DATA
+        select CLOCKSOURCE_VALIDATE_LAST_CYCLE
         select GENERIC_CLOCKEVENTS_BROADCAST if X86_64 || (X86_32 && X86_LOCAL_APIC)
         select GENERIC_TIME_VSYSCALL
         select GENERIC_STRNCPY_FROM_USER
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 57e5ce126d5a..456c0e660c43 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -951,7 +951,7 @@ core_initcall(cpufreq_tsc);
 static struct clocksource clocksource_tsc;
 
 /*
- * We compare the TSC to the cycle_last value in the clocksource
+ * We used to compare the TSC to the cycle_last value in the clocksource
  * structure to avoid a nasty time-warp. This can be observed in a
  * very small window right after one CPU updated cycle_last under
  * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which
@@ -961,26 +961,23 @@ static struct clocksource clocksource_tsc;
  * due to the unsigned delta calculation of the time keeping core
  * code, which is necessary to support wrapping clocksources like pm
  * timer.
+ *
+ * This sanity check is now done in the core timekeeping code.
+ * checking the result of read_tsc() - cycle_last for being negative.
+ * That works because CLOCKSOURCE_MASK(64) does not mask out any bit.
  */
 static cycle_t read_tsc(struct clocksource *cs)
 {
-        cycle_t ret = (cycle_t)get_cycles();
-
-        return ret >= clocksource_tsc.cycle_last ?
-                ret : clocksource_tsc.cycle_last;
-}
-
-static void resume_tsc(struct clocksource *cs)
-{
-        if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3))
-                clocksource_tsc.cycle_last = 0;
+        return (cycle_t)get_cycles();
 }
 
+/*
+ * .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc()
+ */
 static struct clocksource clocksource_tsc = {
         .name                   = "tsc",
         .rating                 = 300,
         .read                   = read_tsc,
-        .resume                 = resume_tsc,
         .mask                   = CLOCKSOURCE_MASK(64),
         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
                                   CLOCK_SOURCE_MUST_VERIFY,
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index feccfd888732..d626dc98e8df 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -12,6 +12,11 @@ config CLOCKSOURCE_WATCHDOG
 config ARCH_CLOCKSOURCE_DATA
         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 05dfa6b25dc4..4ea005a7f9da 100644
--- a/kernel/time/timekeeping_internal.h
+++ b/kernel/time/timekeeping_internal.h
@@ -12,9 +12,18 @@ extern void tk_debug_account_sleep_time(struct timespec64 *t);
 #define tk_debug_account_sleep_time(x)
 #endif
 
+#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE
+static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
+{
+        cycle_t ret = (now - last) & mask;
+
+        return (s64) ret > 0 ? ret : 0;
+}
+#else
 static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
 {
         return (now - last) & mask;
 }
+#endif
 
 #endif /* _TIMEKEEPING_INTERNAL_H */