1 files changed, 28 insertions, 16 deletions

diff --git a/arch/x86/include/asm/vdso/gettimeofday.h b/arch/x86/include/asm/vdso/gettimeofday.h
index 8e048ca980..0ef36190ab 100644
--- a/arch/x86/include/asm/vdso/gettimeofday.h
+++ b/arch/x86/include/asm/vdso/gettimeofday.h
@@ -300,7 +300,7 @@ static inline bool arch_vdso_cycles_ok(u64 cycles)
 #define vdso_cycles_ok arch_vdso_cycles_ok
 
 /*
- * x86 specific delta calculation.
+ * x86 specific calculation of nanoseconds for the current cycle count
  *
  * The regular implementation assumes that clocksource reads are globally
  * monotonic. The TSC can be slightly off across sockets which can cause
@@ -308,8 +308,8 @@ static inline bool arch_vdso_cycles_ok(u64 cycles)
  * jump.
  *
  * Therefore it needs to be verified that @cycles are greater than
- * @last. If not then use @last, which is the base time of the current
- * conversion period.
+ * @vd->cycles_last. If not then use @vd->cycles_last, which is the base
+ * time of the current conversion period.
  *
  * This variant also uses a custom mask because while the clocksource mask of
  * all the VDSO capable clocksources on x86 is U64_MAX, the above code uses
@@ -317,25 +317,37 @@ static inline bool arch_vdso_cycles_ok(u64 cycles)
  * declares everything with the MSB/Sign-bit set as invalid. Therefore the
  * effective mask is S64_MAX.
  */
-static __always_inline
-u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult)
+static __always_inline u64 vdso_calc_ns(const struct vdso_data *vd, u64 cycles, u64 base)
 {
-	/*
-	 * Due to the MSB/Sign-bit being used as invalid marker (see
-	 * arch_vdso_cycles_valid() above), the effective mask is S64_MAX.
-	 */
-	u64 delta = (cycles - last) & S64_MAX;
+	u64 delta = cycles - vd->cycle_last;
 
 	/*
-	 * Due to the above mentioned TSC wobbles, filter out negative motion.
-	 * Per the above masking, the effective sign bit is now bit 62.
+	 * Negative motion and deltas which can cause multiplication
+	 * overflow require special treatment. This check covers both as
+	 * negative motion is guaranteed to be greater than @vd::max_cycles
+	 * due to unsigned comparison.
+	 *
+	 * Due to the MSB/Sign-bit being used as invalid marker (see
+	 * arch_vdso_cycles_valid() above), the effective mask is S64_MAX,
+	 * but that case is also unlikely and will also take the unlikely path
+	 * here.
 	 */
-	if (unlikely(delta & (1ULL << 62)))
-		return 0;
+	if (unlikely(delta > vd->max_cycles)) {
+		/*
+		 * Due to the above mentioned TSC wobbles, filter out
+		 * negative motion.  Per the above masking, the effective
+		 * sign bit is now bit 62.
+		 */
+		if (delta & (1ULL << 62))
+			return base >> vd->shift;
+
+		/* Handle multiplication overflow gracefully */
+		return mul_u64_u32_add_u64_shr(delta & S64_MAX, vd->mult, base, vd->shift);
+	}
 
-	return delta * mult;
+	return ((delta * vd->mult) + base) >> vd->shift;
 }
-#define vdso_calc_delta vdso_calc_delta
+#define vdso_calc_ns vdso_calc_ns
 
 #endif /* !__ASSEMBLY__ */