--- a/arch/x86/include/asm/timer.h	2014-07-07 09:44:22.087054001 +0900
+++ b/arch/x86/include/asm/timer.h	2014-07-07 09:44:55.877054001 +0900
@@ -63,14 +63,10 @@
 
 static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
 {
-	unsigned long long quot;
-	unsigned long long rem;
 	int cpu = smp_processor_id();
 	unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
-	quot = (cyc >> CYC2NS_SCALE_FACTOR);
-	rem = cyc & ((1ULL << CYC2NS_SCALE_FACTOR) - 1);
-	ns += quot * per_cpu(cyc2ns, cpu) +
-		((rem * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR);
+	ns += mult_frac(cyc, per_cpu(cyc2ns, cpu),
+ 		(1UL << CYC2NS_SCALE_FACTOR));
 	return ns;
 }
 
--- a/arch/x86/kernel/tsc.c	2014-07-07 09:45:13.257054001 +0900
+++ b/arch/x86/kernel/tsc.c	2014-07-07 09:48:02.817054001 +0900
@@ -625,7 +625,7 @@
 
 	if (cpu_khz) {
 		*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
-		*offset = ns_now - (tsc_now * *scale >> CYC2NS_SCALE_FACTOR);
+		  *offset = ns_now - mult_frac(tsc_now, *scale, (1UL << CYC2NS_SCALE_FACTOR));
 	}
 
 	sched_clock_idle_wakeup_event(0);
--- a/include/linux/kernel.h	2014-07-07 09:48:23.607054001 +0900
+++ b/include/linux/kernel.h	2014-07-07 09:50:31.627054001 +0900
@@ -66,6 +66,19 @@
 }							\
 )
 
+/*
+ * Multiplies an integer by a fraction, while avoiding unnecessary
+ * overflow or loss of precision.
+ */
+#define mult_frac(x, numer, denom)( \
+{ \
+	typeof(x) quot = (x) / (denom); \
+	typeof(x) rem = (x) % (denom); \
+	(quot * (numer)) + ((rem * (numer)) / (denom)); \
+} \
+)
+
+
 #define _RET_IP_		(unsigned long)__builtin_return_address(0)
 #define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })