3 files changed, 30 insertions, 2 deletions

diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index fba4d66788a2..4c060bb5b8ea 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -128,4 +128,32 @@ static inline unsigned long long get_clock_monotonic(void)
         return get_clock_xt() - sched_clock_base_cc;
 }
 
+/**
+ * tod_to_ns - convert a TOD format value to nanoseconds
+ * @todval: to be converted TOD format value
+ * Returns: number of nanoseconds that correspond to the TOD format value
+ *
+ * Converting a 64 Bit TOD format value to nanoseconds means that the value
+ * must be divided by 4.096. In order to achieve that we multiply with 125
+ * and divide by 512:
+ *
+ *    ns = (todval * 125) >> 9;
+ *
+ * In order to avoid an overflow with the multiplication we can rewrite this.
+ * With a split todval == 2^32 * th + tl (th upper 32 bits, tl lower 32 bits)
+ * we end up with
+ *
+ *    ns = ((2^32 * th + tl) * 125 ) >> 9;
+ * -> ns = (2^23 * th * 125) + ((tl * 125) >> 9);
+ *
+ */
+static inline unsigned long long tod_to_ns(unsigned long long todval)
+{
+        unsigned long long ns;
+
+        ns = ((todval >> 32) << 23) * 125;
+        ns += ((todval & 0xffffffff) * 125) >> 9;
+        return ns;
+}
+
 #endif
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index aff0e350d776..a5f4f5a1d24b 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -63,7 +63,7 @@ static DEFINE_PER_CPU(struct clock_event_device, comparators);
  */
 unsigned long long notrace __kprobes sched_clock(void)
 {
-        return (get_clock_monotonic() * 125) >> 9;
+        return tod_to_ns(get_clock_monotonic());
 }
 
 /*
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index c30615e605ac..82c481ddef76 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -408,7 +408,7 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
                 return 0;
         }
 
-        sltime = ((vcpu->arch.sie_block->ckc - now)*125)>>9;
+        sltime = tod_to_ns(vcpu->arch.sie_block->ckc - now);
 
         hrtimer_start(&vcpu->arch.ckc_timer, ktime_set (0, sltime) , HRTIMER_MODE_REL);
         VCPU_EVENT(vcpu, 5, "enabled wait via clock comparator: %llx ns", sltime);