3 files changed, 36 insertions, 5 deletions

diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index 95640dcd1899..05af9a334893 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -42,6 +42,7 @@ struct tk_read_base {
  * struct timekeeper - Structure holding internal timekeeping values.
  * @tkr:                The readout base structure
  * @xtime_sec:          Current CLOCK_REALTIME time in seconds
+ * @ktime_sec:          Current CLOCK_MONOTONIC time in seconds
  * @wall_to_monotonic:  CLOCK_REALTIME to CLOCK_MONOTONIC offset
  * @offs_real:          Offset clock monotonic -> clock realtime
  * @offs_boot:          Offset clock monotonic -> clock boottime
@@ -77,6 +78,7 @@ struct tk_read_base {
 struct timekeeper {
         struct tk_read_base     tkr;
         u64                     xtime_sec;
+        unsigned long           ktime_sec;
         struct timespec64       wall_to_monotonic;
         ktime_t                 offs_real;
         ktime_t                 offs_boot;
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 1caa6b04fdc5..115d55e11bc9 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -28,6 +28,7 @@ struct timespec __current_kernel_time(void);
 struct timespec get_monotonic_coarse(void);
 extern void getrawmonotonic(struct timespec *ts);
 extern void ktime_get_ts64(struct timespec64 *ts);
+extern time64_t ktime_get_seconds(void);
 
 extern int __getnstimeofday64(struct timespec64 *tv);
 extern void getnstimeofday64(struct timespec64 *tv);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index ec1791fae965..a693270efafb 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -417,7 +417,8 @@ EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
  */
 static inline void tk_update_ktime_data(struct timekeeper *tk)
 {
-        s64 nsec;
+        u64 seconds;
+        u32 nsec;
 
         /*
          * The xtime based monotonic readout is:
@@ -426,13 +427,22 @@ static inline void tk_update_ktime_data(struct timekeeper *tk)
          *      nsec = base_mono + now();
          * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec
          */
-        nsec = (s64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec);
-        nsec *= NSEC_PER_SEC;
-        nsec += tk->wall_to_monotonic.tv_nsec;
-        tk->tkr.base_mono = ns_to_ktime(nsec);
+        seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec);
+        nsec = (u32) tk->wall_to_monotonic.tv_nsec;
+        tk->tkr.base_mono = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);
 
         /* Update the monotonic raw base */
         tk->base_raw = timespec64_to_ktime(tk->raw_time);
+
+        /*
+         * The sum of the nanoseconds portions of xtime and
+         * wall_to_monotonic can be greater/equal one second. Take
+         * this into account before updating tk->ktime_sec.
+         */
+        nsec += (u32)(tk->tkr.xtime_nsec >> tk->tkr.shift);
+        if (nsec >= NSEC_PER_SEC)
+                seconds++;
+        tk->ktime_sec = seconds;
 }
 
 /* must hold timekeeper_lock */
@@ -648,6 +658,24 @@ void ktime_get_ts64(struct timespec64 *ts)
 }
 EXPORT_SYMBOL_GPL(ktime_get_ts64);
 
+/**
+ * ktime_get_seconds - Get the seconds portion of CLOCK_MONOTONIC
+ *
+ * Returns the seconds portion of CLOCK_MONOTONIC with a single non
+ * serialized read. tk->ktime_sec is of type 'unsigned long' so this
+ * works on both 32 and 64 bit systems. On 32 bit systems the readout
+ * covers ~136 years of uptime which should be enough to prevent
+ * premature wrap arounds.
+ */
+time64_t ktime_get_seconds(void)
+{
+        struct timekeeper *tk = &tk_core.timekeeper;
+
+        WARN_ON(timekeeping_suspended);
+        return tk->ktime_sec;
+}
+EXPORT_SYMBOL_GPL(ktime_get_seconds);
+
 #ifdef CONFIG_NTP_PPS
 
 /**