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 // SPDX-License-Identifier: GPL-2.0
 /*
  *  Kernel timekeeping code and accessor functions. Based on code from
  *  timer.c, moved in commit 8524070b7982.
  */
 #include <linux/timekeeper_internal.h>
 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/nmi.h>
 #include <linux/sched.h>
 #include <linux/sched/loadavg.h>
 #include <linux/sched/clock.h>
 #include <linux/syscore_ops.h>
 #include <linux/clocksource.h>
 #include <linux/jiffies.h>
 #include <linux/time.h>
 #include <linux/timex.h>
 #include <linux/tick.h>
 #include <linux/stop_machine.h>
 #include <linux/pvclock_gtod.h>
 #include <linux/compiler.h>
 #include <linux/audit.h>
 #include <linux/random.h>
 
 #include "tick-internal.h"
 #include "ntp_internal.h"
 #include "timekeeping_internal.h"
 
 #define TK_CLEAR_NTP        (1 << 0)
 #define TK_MIRROR       (1 << 1)
 #define TK_CLOCK_WAS_SET    (1 << 2)
 
 enum timekeeping_adv_mode {
     /* Update timekeeper when a tick has passed */
     TK_ADV_TICK,
 
     /* Update timekeeper on a direct frequency change */
     TK_ADV_FREQ
 };
 
 DEFINE_RAW_SPINLOCK(timekeeper_lock);
 
 /*
  * The most important data for readout fits into a single 64 byte
  * cache line.
  */
 static struct {
     seqcount_raw_spinlock_t seq;
     struct timekeeper   timekeeper;
 } tk_core ____cacheline_aligned = {
     .seq = SEQCNT_RAW_SPINLOCK_ZERO(tk_core.seq, &timekeeper_lock),
 };
 
 static struct timekeeper shadow_timekeeper;
 
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
 
 /**
  * struct tk_fast - NMI safe timekeeper
  * @seq:    Sequence counter for protecting updates. The lowest bit
  *      is the index for the tk_read_base array
  * @base:   tk_read_base array. Access is indexed by the lowest bit of
  *      @seq.
  *
  * See @update_fast_timekeeper() below.
  */
 struct tk_fast {
     seqcount_latch_t    seq;
     struct tk_read_base base[2];
 };
 
 /* Suspend-time cycles value for halted fast timekeeper. */
 static u64 cycles_at_suspend;
 
 static u64 dummy_clock_read(struct clocksource *cs)
 {
     if (timekeeping_suspended)
         return cycles_at_suspend;
     return local_clock();
 }
 
 static struct clocksource dummy_clock = {
     .read = dummy_clock_read,
 };
 
 /*
  * Boot time initialization which allows local_clock() to be utilized
  * during early boot when clocksources are not available. local_clock()
  * returns nanoseconds already so no conversion is required, hence mult=1
  * and shift=0. When the first proper clocksource is installed then
  * the fast time keepers are updated with the correct values.
  */
 #define FAST_TK_INIT                        \
     {                           \
         .clock      = &dummy_clock,         \
         .mask       = CLOCKSOURCE_MASK(64),     \
         .mult       = 1,                \
         .shift      = 0,                \
     }
 
 static struct tk_fast tk_fast_mono ____cacheline_aligned = {
     .seq     = SEQCNT_LATCH_ZERO(tk_fast_mono.seq),
     .base[0] = FAST_TK_INIT,
     .base[1] = FAST_TK_INIT,
 };
 
 static struct tk_fast tk_fast_raw  ____cacheline_aligned = {
     .seq     = SEQCNT_LATCH_ZERO(tk_fast_raw.seq),
     .base[0] = FAST_TK_INIT,
     .base[1] = FAST_TK_INIT,
 };
 
 static inline void tk_normalize_xtime(struct timekeeper *tk)
 {
     while (tk->tkr_mono.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr_mono.shift)) {
         tk->tkr_mono.xtime_nsec -= (u64)NSEC_PER_SEC << tk->tkr_mono.shift;
         tk->xtime_sec++;
     }
     while (tk->tkr_raw.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr_raw.shift)) {
         tk->tkr_raw.xtime_nsec -= (u64)NSEC_PER_SEC << tk->tkr_raw.shift;
         tk->raw_sec++;
     }
 }
 
 static inline struct timespec64 tk_xtime(const struct timekeeper *tk)
 {
     struct timespec64 ts;
 
     ts.tv_sec = tk->xtime_sec;
     ts.tv_nsec = (long)(tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift);
     return ts;
 }
 
 static void tk_set_xtime(struct timekeeper *tk, const struct timespec64 *ts)
 {
     tk->xtime_sec = ts->tv_sec;
     tk->tkr_mono.xtime_nsec = (u64)ts->tv_nsec << tk->tkr_mono.shift;
 }
 
 static void tk_xtime_add(struct timekeeper *tk, const struct timespec64 *ts)
 {
     tk->xtime_sec += ts->tv_sec;
     tk->tkr_mono.xtime_nsec += (u64)ts->tv_nsec << tk->tkr_mono.shift;
     tk_normalize_xtime(tk);
 }
 
 static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec64 wtm)
 {
     struct timespec64 tmp;
 
     /*
      * Verify consistency of: offset_real = -wall_to_monotonic
      * before modifying anything
      */
     set_normalized_timespec64(&tmp, -tk->wall_to_monotonic.tv_sec,
                     -tk->wall_to_monotonic.tv_nsec);
     WARN_ON_ONCE(tk->offs_real != timespec64_to_ktime(tmp));
     tk->wall_to_monotonic = wtm;
     set_normalized_timespec64(&tmp, -wtm.tv_sec, -wtm.tv_nsec);
     tk->offs_real = timespec64_to_ktime(tmp);
     tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tk->tai_offset, 0));
 }
 
 static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
 {
     tk->offs_boot = ktime_add(tk->offs_boot, delta);
     /*
      * Timespec representation for VDSO update to avoid 64bit division
      * on every update.
      */
     tk->monotonic_to_boot = ktime_to_timespec64(tk->offs_boot);
 }
 
 /*
  * tk_clock_read - atomic clocksource read() helper
  *
  * This helper is necessary to use in the read paths because, while the
  * seqcount ensures we don't return a bad value while structures are updated,
  * it doesn't protect from potential crashes. There is the possibility that
  * the tkr's clocksource may change between the read reference, and the
  * clock reference passed to the read function.  This can cause crashes if
  * the wrong clocksource is passed to the wrong read function.
  * This isn't necessary to use when holding the timekeeper_lock or doing
  * a read of the fast-timekeeper tkrs (which is protected by its own locking
  * and update logic).
  */
 static inline u64 tk_clock_read(const struct tk_read_base *tkr)
 {
     struct clocksource *clock = READ_ONCE(tkr->clock);
 
     return clock->read(clock);
 }
 
 #ifdef CONFIG_DEBUG_TIMEKEEPING
 #define WARNING_FREQ (HZ*300) /* 5 minute rate-limiting */
 
 static void timekeeping_check_update(struct timekeeper *tk, u64 offset)
 {
 
     u64 max_cycles = tk->tkr_mono.clock->max_cycles;
     const char *name = tk->tkr_mono.clock->name;
 
     if (offset > max_cycles) {
         printk_deferred("WARNING: timekeeping: Cycle offset (%lld) is larger than allowed by the '%s' clock's max_cycles value (%lld): time overflow danger\n",
                 offset, name, max_cycles);
         printk_deferred("         timekeeping: Your kernel is sick, but tries to cope by capping time updates\n");
     } else {
         if (offset > (max_cycles >> 1)) {
             printk_deferred("INFO: timekeeping: Cycle offset (%lld) is larger than the '%s' clock's 50%% safety margin (%lld)\n",
                     offset, name, max_cycles >> 1);
             printk_deferred("      timekeeping: Your kernel is still fine, but is feeling a bit nervous\n");
         }
     }
 
     if (tk->underflow_seen) {
         if (jiffies - tk->last_warning > WARNING_FREQ) {
             printk_deferred("WARNING: Underflow in clocksource '%s' observed, time update ignored.\n", name);
             printk_deferred("         Please report this, consider using a different clocksource, if possible.\n");
             printk_deferred("         Your kernel is probably still fine.\n");
             tk->last_warning = jiffies;
         }
         tk->underflow_seen = 0;
     }
 
     if (tk->overflow_seen) {
         if (jiffies - tk->last_warning > WARNING_FREQ) {
             printk_deferred("WARNING: Overflow in clocksource '%s' observed, time update capped.\n", name);
             printk_deferred("         Please report this, consider using a different clocksource, if possible.\n");
             printk_deferred("         Your kernel is probably still fine.\n");
             tk->last_warning = jiffies;
         }
         tk->overflow_seen = 0;
     }
 }
 
 static inline u64 timekeeping_get_delta(const struct tk_read_base *tkr)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     u64 now, last, mask, max, delta;
     unsigned int seq;
 
     /*
      * Since we're called holding a seqcount, the data may shift
      * under us while we're doing the calculation. This can cause
      * false positives, since we'd note a problem but throw the
      * results away. So nest another seqcount here to atomically
      * grab the points we are checking with.
      */
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         now = tk_clock_read(tkr);
         last = tkr->cycle_last;
         mask = tkr->mask;
         max = tkr->clock->max_cycles;
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     delta = clocksource_delta(now, last, mask);
 
     /*
      * Try to catch underflows by checking if we are seeing small
      * mask-relative negative values.
      */
     if (unlikely((~delta & mask) < (mask >> 3))) {
         tk->underflow_seen = 1;
         delta = 0;
     }
 
     /* Cap delta value to the max_cycles values to avoid mult overflows */
     if (unlikely(delta > max)) {
         tk->overflow_seen = 1;
         delta = tkr->clock->max_cycles;
     }
 
     return delta;
 }
 #else
 static inline void timekeeping_check_update(struct timekeeper *tk, u64 offset)
 {
 }
 static inline u64 timekeeping_get_delta(const struct tk_read_base *tkr)
 {
     u64 cycle_now, delta;
 
     /* read clocksource */
     cycle_now = tk_clock_read(tkr);
 
     /* calculate the delta since the last update_wall_time */
     delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask);
 
     return delta;
 }
 #endif
 
 /**
  * tk_setup_internals - Set up internals to use clocksource clock.
  *
  * @tk:     The target timekeeper to setup.
  * @clock:      Pointer to clocksource.
  *
  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
  * pair and interval request.
  *
  * Unless you're the timekeeping code, you should not be using this!
  */
 static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock)
 {
     u64 interval;
     u64 tmp, ntpinterval;
     struct clocksource *old_clock;
 
     ++tk->cs_was_changed_seq;
     old_clock = tk->tkr_mono.clock;
     tk->tkr_mono.clock = clock;
     tk->tkr_mono.mask = clock->mask;
     tk->tkr_mono.cycle_last = tk_clock_read(&tk->tkr_mono);
 
     tk->tkr_raw.clock = clock;
     tk->tkr_raw.mask = clock->mask;
     tk->tkr_raw.cycle_last = tk->tkr_mono.cycle_last;
 
     /* Do the ns -> cycle conversion first, using original mult */
     tmp = NTP_INTERVAL_LENGTH;
     tmp <<= clock->shift;
     ntpinterval = tmp;
     tmp += clock->mult/2;
     do_div(tmp, clock->mult);
     if (tmp == 0)
         tmp = 1;
 
     interval = (u64) tmp;
     tk->cycle_interval = interval;
 
     /* Go back from cycles -> shifted ns */
     tk->xtime_interval = interval * clock->mult;
     tk->xtime_remainder = ntpinterval - tk->xtime_interval;
     tk->raw_interval = interval * clock->mult;
 
      /* if changing clocks, convert xtime_nsec shift units */
     if (old_clock) {
         int shift_change = clock->shift - old_clock->shift;
         if (shift_change < 0) {
             tk->tkr_mono.xtime_nsec >>= -shift_change;
             tk->tkr_raw.xtime_nsec >>= -shift_change;
         } else {
             tk->tkr_mono.xtime_nsec <<= shift_change;
             tk->tkr_raw.xtime_nsec <<= shift_change;
         }
     }
 
     tk->tkr_mono.shift = clock->shift;
     tk->tkr_raw.shift = clock->shift;
 
     tk->ntp_error = 0;
     tk->ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;
     tk->ntp_tick = ntpinterval << tk->ntp_error_shift;
 
     /*
      * The timekeeper keeps its own mult values for the currently
      * active clocksource. These value will be adjusted via NTP
      * to counteract clock drifting.
      */
     tk->tkr_mono.mult = clock->mult;
     tk->tkr_raw.mult = clock->mult;
     tk->ntp_err_mult = 0;
     tk->skip_second_overflow = 0;
 }
 
 /* Timekeeper helper functions. */
 
 static inline u64 timekeeping_delta_to_ns(const struct tk_read_base *tkr, u64 delta)
 {
     u64 nsec;
 
     nsec = delta * tkr->mult + tkr->xtime_nsec;
     nsec >>= tkr->shift;
 
     return nsec;
 }
 
 static inline u64 timekeeping_get_ns(const struct tk_read_base *tkr)
 {
     u64 delta;
 
     delta = timekeeping_get_delta(tkr);
     return timekeeping_delta_to_ns(tkr, delta);
 }
 
 static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 cycles)
 {
     u64 delta;
 
     /* calculate the delta since the last update_wall_time */
     delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
     return timekeeping_delta_to_ns(tkr, delta);
 }
 
 /**
  * update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper.
  * @tkr: Timekeeping readout base from which we take the update
  * @tkf: Pointer to NMI safe timekeeper
  *
  * We want to use this from any context including NMI and tracing /
  * instrumenting the timekeeping code itself.
  *
  * Employ the latch technique; see @raw_write_seqcount_latch.
  *
  * So if a NMI hits the update of base[0] then it will use base[1]
  * which is still consistent. In the worst case this can result is a
  * slightly wrong timestamp (a few nanoseconds). See
  * @ktime_get_mono_fast_ns.
  */
 static void update_fast_timekeeper(const struct tk_read_base *tkr,
                    struct tk_fast *tkf)
 {
     struct tk_read_base *base = tkf->base;
 
     /* Force readers off to base[1] */
     raw_write_seqcount_latch(&tkf->seq);
 
     /* Update base[0] */
     memcpy(base, tkr, sizeof(*base));
 
     /* Force readers back to base[0] */
     raw_write_seqcount_latch(&tkf->seq);
 
     /* Update base[1] */
     memcpy(base + 1, base, sizeof(*base));
 }
 
 static __always_inline u64 fast_tk_get_delta_ns(struct tk_read_base *tkr)
 {
     u64 delta, cycles = tk_clock_read(tkr);
 
     delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
     return timekeeping_delta_to_ns(tkr, delta);
 }
 
 static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
 {
     struct tk_read_base *tkr;
     unsigned int seq;
     u64 now;
 
     do {
         seq = raw_read_seqcount_latch(&tkf->seq);
         tkr = tkf->base + (seq & 0x01);
         now = ktime_to_ns(tkr->base);
         now += fast_tk_get_delta_ns(tkr);
     } while (read_seqcount_latch_retry(&tkf->seq, seq));
 
     return now;
 }
 
 /**
  * ktime_get_mono_fast_ns - Fast NMI safe access to clock monotonic
  *
  * This timestamp is not guaranteed to be monotonic across an update.
  * The timestamp is calculated by:
  *
  *  now = base_mono + clock_delta * slope
  *
  * So if the update lowers the slope, readers who are forced to the
  * not yet updated second array are still using the old steeper slope.
  *
  * tmono
  * ^
  * |    o  n
  * |   o n
  * |  u
  * | o
  * |o
  * |12345678---> reader order
  *
  * o = old slope
  * u = update
  * n = new slope
  *
  * So reader 6 will observe time going backwards versus reader 5.
  *
  * While other CPUs are likely to be able to observe that, the only way
  * for a CPU local observation is when an NMI hits in the middle of
  * the update. Timestamps taken from that NMI context might be ahead
  * of the following timestamps. Callers need to be aware of that and
  * deal with it.
  */
 u64 notrace ktime_get_mono_fast_ns(void)
 {
     return __ktime_get_fast_ns(&tk_fast_mono);
 }
 EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);
 
 /**
  * ktime_get_raw_fast_ns - Fast NMI safe access to clock monotonic raw
  *
  * Contrary to ktime_get_mono_fast_ns() this is always correct because the
  * conversion factor is not affected by NTP/PTP correction.
  */
 u64 notrace ktime_get_raw_fast_ns(void)
 {
     return __ktime_get_fast_ns(&tk_fast_raw);
 }
 EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns);
 
 /**
  * ktime_get_boot_fast_ns - NMI safe and fast access to boot clock.
  *
  * To keep it NMI safe since we're accessing from tracing, we're not using a
  * separate timekeeper with updates to monotonic clock and boot offset
  * protected with seqcounts. This has the following minor side effects:
  *
  * (1) Its possible that a timestamp be taken after the boot offset is updated
  * but before the timekeeper is updated. If this happens, the new boot offset
  * is added to the old timekeeping making the clock appear to update slightly
  * earlier:
  *    CPU 0                                        CPU 1
  *    timekeeping_inject_sleeptime64()
  *    __timekeeping_inject_sleeptime(tk, delta);
  *                                                 timestamp();
  *    timekeeping_update(tk, TK_CLEAR_NTP...);
  *
  * (2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be
  * partially updated.  Since the tk->offs_boot update is a rare event, this
  * should be a rare occurrence which postprocessing should be able to handle.
  *
  * The caveats vs. timestamp ordering as documented for ktime_get_fast_ns()
  * apply as well.
  */
 u64 notrace ktime_get_boot_fast_ns(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
 
     return (ktime_get_mono_fast_ns() + ktime_to_ns(data_race(tk->offs_boot)));
 }
 EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns);
 
 /**
  * ktime_get_tai_fast_ns - NMI safe and fast access to tai clock.
  *
  * The same limitations as described for ktime_get_boot_fast_ns() apply. The
  * mono time and the TAI offset are not read atomically which may yield wrong
  * readouts. However, an update of the TAI offset is an rare event e.g., caused
  * by settime or adjtimex with an offset. The user of this function has to deal
  * with the possibility of wrong timestamps in post processing.
  */
 u64 notrace ktime_get_tai_fast_ns(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
 
     return (ktime_get_mono_fast_ns() + ktime_to_ns(data_race(tk->offs_tai)));
 }
 EXPORT_SYMBOL_GPL(ktime_get_tai_fast_ns);
 
 static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono)
 {
     struct tk_read_base *tkr;
     u64 basem, baser, delta;
     unsigned int seq;
 
     do {
         seq = raw_read_seqcount_latch(&tkf->seq);
         tkr = tkf->base + (seq & 0x01);
         basem = ktime_to_ns(tkr->base);
         baser = ktime_to_ns(tkr->base_real);
         delta = fast_tk_get_delta_ns(tkr);
     } while (read_seqcount_latch_retry(&tkf->seq, seq));
 
     if (mono)
         *mono = basem + delta;
     return baser + delta;
 }
 
 /**
  * ktime_get_real_fast_ns: - NMI safe and fast access to clock realtime.
  *
  * See ktime_get_fast_ns() for documentation of the time stamp ordering.
  */
 u64 ktime_get_real_fast_ns(void)
 {
     return __ktime_get_real_fast(&tk_fast_mono, NULL);
 }
 EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns);
 
 /**
  * ktime_get_fast_timestamps: - NMI safe timestamps
  * @snapshot:   Pointer to timestamp storage
  *
  * Stores clock monotonic, boottime and realtime timestamps.
  *
  * Boot time is a racy access on 32bit systems if the sleep time injection
  * happens late during resume and not in timekeeping_resume(). That could
  * be avoided by expanding struct tk_read_base with boot offset for 32bit
  * and adding more overhead to the update. As this is a hard to observe
  * once per resume event which can be filtered with reasonable effort using
  * the accurate mono/real timestamps, it's probably not worth the trouble.
  *
  * Aside of that it might be possible on 32 and 64 bit to observe the
  * following when the sleep time injection happens late:
  *
  * CPU 0                CPU 1
  * timekeeping_resume()
  * ktime_get_fast_timestamps()
  *  mono, real = __ktime_get_real_fast()
  *                  inject_sleep_time()
  *                     update boot offset
  *  boot = mono + bootoffset;
  *
  * That means that boot time already has the sleep time adjustment, but
  * real time does not. On the next readout both are in sync again.
  *
  * Preventing this for 64bit is not really feasible without destroying the
  * careful cache layout of the timekeeper because the sequence count and
  * struct tk_read_base would then need two cache lines instead of one.
  *
  * Access to the time keeper clock source is disabled across the innermost
  * steps of suspend/resume. The accessors still work, but the timestamps
  * are frozen until time keeping is resumed which happens very early.
  *
  * For regular suspend/resume there is no observable difference vs. sched
  * clock, but it might affect some of the nasty low level debug printks.
  *
  * OTOH, access to sched clock is not guaranteed across suspend/resume on
  * all systems either so it depends on the hardware in use.
  *
  * If that turns out to be a real problem then this could be mitigated by
  * using sched clock in a similar way as during early boot. But it's not as
  * trivial as on early boot because it needs some careful protection
  * against the clock monotonic timestamp jumping backwards on resume.
  */
 void ktime_get_fast_timestamps(struct ktime_timestamps *snapshot)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
 
     snapshot->real = __ktime_get_real_fast(&tk_fast_mono, &snapshot->mono);
     snapshot->boot = snapshot->mono + ktime_to_ns(data_race(tk->offs_boot));
 }
 
 /**
  * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
  * @tk: Timekeeper to snapshot.
  *
  * It generally is unsafe to access the clocksource after timekeeping has been
  * suspended, so take a snapshot of the readout base of @tk and use it as the
  * fast timekeeper's readout base while suspended.  It will return the same
  * number of cycles every time until timekeeping is resumed at which time the
  * proper readout base for the fast timekeeper will be restored automatically.
  */
 static void halt_fast_timekeeper(const struct timekeeper *tk)
 {
     static struct tk_read_base tkr_dummy;
     const struct tk_read_base *tkr = &tk->tkr_mono;
 
     memcpy(&tkr_dummy, tkr, sizeof(tkr_dummy));
     cycles_at_suspend = tk_clock_read(tkr);
     tkr_dummy.clock = &dummy_clock;
     tkr_dummy.base_real = tkr->base + tk->offs_real;
     update_fast_timekeeper(&tkr_dummy, &tk_fast_mono);
 
     tkr = &tk->tkr_raw;
     memcpy(&tkr_dummy, tkr, sizeof(tkr_dummy));
     tkr_dummy.clock = &dummy_clock;
     update_fast_timekeeper(&tkr_dummy, &tk_fast_raw);
 }
 
 static RAW_NOTIFIER_HEAD(pvclock_gtod_chain);
 
 static void update_pvclock_gtod(struct timekeeper *tk, bool was_set)
 {
     raw_notifier_call_chain(&pvclock_gtod_chain, was_set, tk);
 }
 
 /**
  * pvclock_gtod_register_notifier - register a pvclock timedata update listener
  * @nb: Pointer to the notifier block to register
  */
 int pvclock_gtod_register_notifier(struct notifier_block *nb)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned long flags;
     int ret;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     ret = raw_notifier_chain_register(&pvclock_gtod_chain, nb);
     update_pvclock_gtod(tk, true);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(pvclock_gtod_register_notifier);
 
 /**
  * pvclock_gtod_unregister_notifier - unregister a pvclock
  * timedata update listener
  * @nb: Pointer to the notifier block to unregister
  */
 int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
 {
     unsigned long flags;
     int ret;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     ret = raw_notifier_chain_unregister(&pvclock_gtod_chain, nb);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
 
 /*
  * tk_update_leap_state - helper to update the next_leap_ktime
  */
 static inline void tk_update_leap_state(struct timekeeper *tk)
 {
     tk->next_leap_ktime = ntp_get_next_leap();
     if (tk->next_leap_ktime != KTIME_MAX)
         /* Convert to monotonic time */
         tk->next_leap_ktime = ktime_sub(tk->next_leap_ktime, tk->offs_real);
 }
 
 /*
  * Update the ktime_t based scalar nsec members of the timekeeper
  */
 static inline void tk_update_ktime_data(struct timekeeper *tk)
 {
     u64 seconds;
     u32 nsec;
 
     /*
      * The xtime based monotonic readout is:
      *  nsec = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec + now();
      * The ktime based monotonic readout is:
      *  nsec = base_mono + now();
      * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec
      */
     seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec);
     nsec = (u32) tk->wall_to_monotonic.tv_nsec;
     tk->tkr_mono.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec);
 
     /*
      * 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_mono.xtime_nsec >> tk->tkr_mono.shift);
     if (nsec >= NSEC_PER_SEC)
         seconds++;
     tk->ktime_sec = seconds;
 
     /* Update the monotonic raw base */
     tk->tkr_raw.base = ns_to_ktime(tk->raw_sec * NSEC_PER_SEC);
 }
 
 /* must hold timekeeper_lock */
 static void timekeeping_update(struct timekeeper *tk, unsigned int action)
 {
     if (action & TK_CLEAR_NTP) {
         tk->ntp_error = 0;
         ntp_clear();
     }
 
     tk_update_leap_state(tk);
     tk_update_ktime_data(tk);
 
     update_vsyscall(tk);
     update_pvclock_gtod(tk, action & TK_CLOCK_WAS_SET);
 
     tk->tkr_mono.base_real = tk->tkr_mono.base + tk->offs_real;
     update_fast_timekeeper(&tk->tkr_mono, &tk_fast_mono);
     update_fast_timekeeper(&tk->tkr_raw,  &tk_fast_raw);
 
     if (action & TK_CLOCK_WAS_SET)
         tk->clock_was_set_seq++;
     /*
      * The mirroring of the data to the shadow-timekeeper needs
      * to happen last here to ensure we don't over-write the
      * timekeeper structure on the next update with stale data
      */
     if (action & TK_MIRROR)
         memcpy(&shadow_timekeeper, &tk_core.timekeeper,
                sizeof(tk_core.timekeeper));
 }
 
 /**
  * timekeeping_forward_now - update clock to the current time
  * @tk:     Pointer to the timekeeper to update
  *
  * Forward the current clock to update its state since the last call to
  * update_wall_time(). This is useful before significant clock changes,
  * as it avoids having to deal with this time offset explicitly.
  */
 static void timekeeping_forward_now(struct timekeeper *tk)
 {
     u64 cycle_now, delta;
 
     cycle_now = tk_clock_read(&tk->tkr_mono);
     delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last, tk->tkr_mono.mask);
     tk->tkr_mono.cycle_last = cycle_now;
     tk->tkr_raw.cycle_last  = cycle_now;
 
     tk->tkr_mono.xtime_nsec += delta * tk->tkr_mono.mult;
     tk->tkr_raw.xtime_nsec += delta * tk->tkr_raw.mult;
 
     tk_normalize_xtime(tk);
 }
 
 /**
  * ktime_get_real_ts64 - Returns the time of day in a timespec64.
  * @ts:     pointer to the timespec to be set
  *
  * Returns the time of day in a timespec64 (WARN if suspended).
  */
 void ktime_get_real_ts64(struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     u64 nsecs;
 
     WARN_ON(timekeeping_suspended);
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
 
         ts->tv_sec = tk->xtime_sec;
         nsecs = timekeeping_get_ns(&tk->tkr_mono);
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     ts->tv_nsec = 0;
     timespec64_add_ns(ts, nsecs);
 }
 EXPORT_SYMBOL(ktime_get_real_ts64);
 
 ktime_t ktime_get(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     ktime_t base;
     u64 nsecs;
 
     WARN_ON(timekeeping_suspended);
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         base = tk->tkr_mono.base;
         nsecs = timekeeping_get_ns(&tk->tkr_mono);
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return ktime_add_ns(base, nsecs);
 }
 EXPORT_SYMBOL_GPL(ktime_get);
 
 u32 ktime_get_resolution_ns(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     u32 nsecs;
 
     WARN_ON(timekeeping_suspended);
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         nsecs = tk->tkr_mono.mult >> tk->tkr_mono.shift;
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return nsecs;
 }
 EXPORT_SYMBOL_GPL(ktime_get_resolution_ns);
 
 static ktime_t *offsets[TK_OFFS_MAX] = {
     [TK_OFFS_REAL]  = &tk_core.timekeeper.offs_real,
     [TK_OFFS_BOOT]  = &tk_core.timekeeper.offs_boot,
     [TK_OFFS_TAI]   = &tk_core.timekeeper.offs_tai,
 };
 
 ktime_t ktime_get_with_offset(enum tk_offsets offs)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     ktime_t base, *offset = offsets[offs];
     u64 nsecs;
 
     WARN_ON(timekeeping_suspended);
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         base = ktime_add(tk->tkr_mono.base, *offset);
         nsecs = timekeeping_get_ns(&tk->tkr_mono);
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return ktime_add_ns(base, nsecs);
 
 }
 EXPORT_SYMBOL_GPL(ktime_get_with_offset);
 
 ktime_t ktime_get_coarse_with_offset(enum tk_offsets offs)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     ktime_t base, *offset = offsets[offs];
     u64 nsecs;
 
     WARN_ON(timekeeping_suspended);
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         base = ktime_add(tk->tkr_mono.base, *offset);
         nsecs = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return ktime_add_ns(base, nsecs);
 }
 EXPORT_SYMBOL_GPL(ktime_get_coarse_with_offset);
 
 /**
  * ktime_mono_to_any() - convert monotonic time to any other time
  * @tmono:  time to convert.
  * @offs:   which offset to use
  */
 ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs)
 {
     ktime_t *offset = offsets[offs];
     unsigned int seq;
     ktime_t tconv;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         tconv = ktime_add(tmono, *offset);
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return tconv;
 }
 EXPORT_SYMBOL_GPL(ktime_mono_to_any);
 
 /**
  * ktime_get_raw - Returns the raw monotonic time in ktime_t format
  */
 ktime_t ktime_get_raw(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     ktime_t base;
     u64 nsecs;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         base = tk->tkr_raw.base;
         nsecs = timekeeping_get_ns(&tk->tkr_raw);
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return ktime_add_ns(base, nsecs);
 }
 EXPORT_SYMBOL_GPL(ktime_get_raw);
 
 /**
  * ktime_get_ts64 - get the monotonic clock in timespec64 format
  * @ts:     pointer to timespec variable
  *
  * The function calculates the monotonic clock from the realtime
  * clock and the wall_to_monotonic offset and stores the result
  * in normalized timespec64 format in the variable pointed to by @ts.
  */
 void ktime_get_ts64(struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     struct timespec64 tomono;
     unsigned int seq;
     u64 nsec;
 
     WARN_ON(timekeeping_suspended);
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         ts->tv_sec = tk->xtime_sec;
         nsec = timekeeping_get_ns(&tk->tkr_mono);
         tomono = tk->wall_to_monotonic;
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     ts->tv_sec += tomono.tv_sec;
     ts->tv_nsec = 0;
     timespec64_add_ns(ts, nsec + tomono.tv_nsec);
 }
 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);
 
 /**
  * ktime_get_real_seconds - Get the seconds portion of CLOCK_REALTIME
  *
  * Returns the wall clock seconds since 1970.
  *
  * For 64bit systems the fast access to tk->xtime_sec is preserved. On
  * 32bit systems the access must be protected with the sequence
  * counter to provide "atomic" access to the 64bit tk->xtime_sec
  * value.
  */
 time64_t ktime_get_real_seconds(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     time64_t seconds;
     unsigned int seq;
 
     if (IS_ENABLED(CONFIG_64BIT))
         return tk->xtime_sec;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         seconds = tk->xtime_sec;
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return seconds;
 }
 EXPORT_SYMBOL_GPL(ktime_get_real_seconds);
 
 /**
  * __ktime_get_real_seconds - The same as ktime_get_real_seconds
  * but without the sequence counter protect. This internal function
  * is called just when timekeeping lock is already held.
  */
 noinstr time64_t __ktime_get_real_seconds(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
 
     return tk->xtime_sec;
 }
 
 /**
  * ktime_get_snapshot - snapshots the realtime/monotonic raw clocks with counter
  * @systime_snapshot:   pointer to struct receiving the system time snapshot
  */
 void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     ktime_t base_raw;
     ktime_t base_real;
     u64 nsec_raw;
     u64 nsec_real;
     u64 now;
 
     WARN_ON_ONCE(timekeeping_suspended);
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         now = tk_clock_read(&tk->tkr_mono);
         systime_snapshot->cs_id = tk->tkr_mono.clock->id;
         systime_snapshot->cs_was_changed_seq = tk->cs_was_changed_seq;
         systime_snapshot->clock_was_set_seq = tk->clock_was_set_seq;
         base_real = ktime_add(tk->tkr_mono.base,
                       tk_core.timekeeper.offs_real);
         base_raw = tk->tkr_raw.base;
         nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono, now);
         nsec_raw  = timekeeping_cycles_to_ns(&tk->tkr_raw, now);
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     systime_snapshot->cycles = now;
     systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
     systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
 }
 EXPORT_SYMBOL_GPL(ktime_get_snapshot);
 
 /* Scale base by mult/div checking for overflow */
 static int scale64_check_overflow(u64 mult, u64 div, u64 *base)
 {
     u64 tmp, rem;
 
     tmp = div64_u64_rem(*base, div, &rem);
 
     if (((int)sizeof(u64)*8 - fls64(mult) < fls64(tmp)) ||
         ((int)sizeof(u64)*8 - fls64(mult) < fls64(rem)))
         return -EOVERFLOW;
     tmp *= mult;
 
     rem = div64_u64(rem * mult, div);
     *base = tmp + rem;
     return 0;
 }
 
 /**
  * adjust_historical_crosststamp - adjust crosstimestamp previous to current interval
  * @history:            Snapshot representing start of history
  * @partial_history_cycles: Cycle offset into history (fractional part)
  * @total_history_cycles:   Total history length in cycles
  * @discontinuity:      True indicates clock was set on history period
  * @ts:             Cross timestamp that should be adjusted using
  *  partial/total ratio
  *
  * Helper function used by get_device_system_crosststamp() to correct the
  * crosstimestamp corresponding to the start of the current interval to the
  * system counter value (timestamp point) provided by the driver. The
  * total_history_* quantities are the total history starting at the provided
  * reference point and ending at the start of the current interval. The cycle
  * count between the driver timestamp point and the start of the current
  * interval is partial_history_cycles.
  */
 static int adjust_historical_crosststamp(struct system_time_snapshot *history,
                      u64 partial_history_cycles,
                      u64 total_history_cycles,
                      bool discontinuity,
                      struct system_device_crosststamp *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     u64 corr_raw, corr_real;
     bool interp_forward;
     int ret;
 
     if (total_history_cycles == 0 || partial_history_cycles == 0)
         return 0;
 
     /* Interpolate shortest distance from beginning or end of history */
     interp_forward = partial_history_cycles > total_history_cycles / 2;
     partial_history_cycles = interp_forward ?
         total_history_cycles - partial_history_cycles :
         partial_history_cycles;
 
     /*
      * Scale the monotonic raw time delta by:
      *  partial_history_cycles / total_history_cycles
      */
     corr_raw = (u64)ktime_to_ns(
         ktime_sub(ts->sys_monoraw, history->raw));
     ret = scale64_check_overflow(partial_history_cycles,
                      total_history_cycles, &corr_raw);
     if (ret)
         return ret;
 
     /*
      * If there is a discontinuity in the history, scale monotonic raw
      *  correction by:
      *  mult(real)/mult(raw) yielding the realtime correction
      * Otherwise, calculate the realtime correction similar to monotonic
      *  raw calculation
      */
     if (discontinuity) {
         corr_real = mul_u64_u32_div
             (corr_raw, tk->tkr_mono.mult, tk->tkr_raw.mult);
     } else {
         corr_real = (u64)ktime_to_ns(
             ktime_sub(ts->sys_realtime, history->real));
         ret = scale64_check_overflow(partial_history_cycles,
                          total_history_cycles, &corr_real);
         if (ret)
             return ret;
     }
 
     /* Fixup monotonic raw and real time time values */
     if (interp_forward) {
         ts->sys_monoraw = ktime_add_ns(history->raw, corr_raw);
         ts->sys_realtime = ktime_add_ns(history->real, corr_real);
     } else {
         ts->sys_monoraw = ktime_sub_ns(ts->sys_monoraw, corr_raw);
         ts->sys_realtime = ktime_sub_ns(ts->sys_realtime, corr_real);
     }
 
     return 0;
 }
 
 /*
  * cycle_between - true if test occurs chronologically between before and after
  */
 static bool cycle_between(u64 before, u64 test, u64 after)
 {
     if (test > before && test < after)
         return true;
     if (test < before && before > after)
         return true;
     return false;
 }
 
 /**
  * get_device_system_crosststamp - Synchronously capture system/device timestamp
  * @get_time_fn:    Callback to get simultaneous device time and
  *  system counter from the device driver
  * @ctx:        Context passed to get_time_fn()
  * @history_begin:  Historical reference point used to interpolate system
  *  time when counter provided by the driver is before the current interval
  * @xtstamp:        Receives simultaneously captured system and device time
  *
  * Reads a timestamp from a device and correlates it to system time
  */
 int get_device_system_crosststamp(int (*get_time_fn)
                   (ktime_t *device_time,
                    struct system_counterval_t *sys_counterval,
                    void *ctx),
                   void *ctx,
                   struct system_time_snapshot *history_begin,
                   struct system_device_crosststamp *xtstamp)
 {
     struct system_counterval_t system_counterval;
     struct timekeeper *tk = &tk_core.timekeeper;
     u64 cycles, now, interval_start;
     unsigned int clock_was_set_seq = 0;
     ktime_t base_real, base_raw;
     u64 nsec_real, nsec_raw;
     u8 cs_was_changed_seq;
     unsigned int seq;
     bool do_interp;
     int ret;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         /*
          * Try to synchronously capture device time and a system
          * counter value calling back into the device driver
          */
         ret = get_time_fn(&xtstamp->device, &system_counterval, ctx);
         if (ret)
             return ret;
 
         /*
          * Verify that the clocksource associated with the captured
          * system counter value is the same as the currently installed
          * timekeeper clocksource
          */
         if (tk->tkr_mono.clock != system_counterval.cs)
             return -ENODEV;
         cycles = system_counterval.cycles;
 
         /*
          * Check whether the system counter value provided by the
          * device driver is on the current timekeeping interval.
          */
         now = tk_clock_read(&tk->tkr_mono);
         interval_start = tk->tkr_mono.cycle_last;
         if (!cycle_between(interval_start, cycles, now)) {
             clock_was_set_seq = tk->clock_was_set_seq;
             cs_was_changed_seq = tk->cs_was_changed_seq;
             cycles = interval_start;
             do_interp = true;
         } else {
             do_interp = false;
         }
 
         base_real = ktime_add(tk->tkr_mono.base,
                       tk_core.timekeeper.offs_real);
         base_raw = tk->tkr_raw.base;
 
         nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono,
                              system_counterval.cycles);
         nsec_raw = timekeeping_cycles_to_ns(&tk->tkr_raw,
                             system_counterval.cycles);
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     xtstamp->sys_realtime = ktime_add_ns(base_real, nsec_real);
     xtstamp->sys_monoraw = ktime_add_ns(base_raw, nsec_raw);
 
     /*
      * Interpolate if necessary, adjusting back from the start of the
      * current interval
      */
     if (do_interp) {
         u64 partial_history_cycles, total_history_cycles;
         bool discontinuity;
 
         /*
          * Check that the counter value occurs after the provided
          * history reference and that the history doesn't cross a
          * clocksource change
          */
         if (!history_begin ||
             !cycle_between(history_begin->cycles,
                    system_counterval.cycles, cycles) ||
             history_begin->cs_was_changed_seq != cs_was_changed_seq)
             return -EINVAL;
         partial_history_cycles = cycles - system_counterval.cycles;
         total_history_cycles = cycles - history_begin->cycles;
         discontinuity =
             history_begin->clock_was_set_seq != clock_was_set_seq;
 
         ret = adjust_historical_crosststamp(history_begin,
                             partial_history_cycles,
                             total_history_cycles,
                             discontinuity, xtstamp);
         if (ret)
             return ret;
     }
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(get_device_system_crosststamp);
 
 /**
  * do_settimeofday64 - Sets the time of day.
  * @ts:     pointer to the timespec64 variable containing the new time
  *
  * Sets the time of day to the new time and update NTP and notify hrtimers
  */
 int do_settimeofday64(const struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     struct timespec64 ts_delta, xt;
     unsigned long flags;
     int ret = 0;
 
     if (!timespec64_valid_settod(ts))
         return -EINVAL;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
 
     timekeeping_forward_now(tk);
 
     xt = tk_xtime(tk);
     ts_delta = timespec64_sub(*ts, xt);
 
     if (timespec64_compare(&tk->wall_to_monotonic, &ts_delta) > 0) {
         ret = -EINVAL;
         goto out;
     }
 
     tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta));
 
     tk_set_xtime(tk, ts);
 out:
     timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);
 
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     /* Signal hrtimers about time change */
     clock_was_set(CLOCK_SET_WALL);
 
     if (!ret) {
         audit_tk_injoffset(ts_delta);
         add_device_randomness(ts, sizeof(*ts));
     }
 
     return ret;
 }
 EXPORT_SYMBOL(do_settimeofday64);
 
 /**
  * timekeeping_inject_offset - Adds or subtracts from the current time.
  * @ts:     Pointer to the timespec variable containing the offset
  *
  * Adds or subtracts an offset value from the current time.
  */
 static int timekeeping_inject_offset(const struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned long flags;
     struct timespec64 tmp;
     int ret = 0;
 
     if (ts->tv_nsec < 0 || ts->tv_nsec >= NSEC_PER_SEC)
         return -EINVAL;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
 
     timekeeping_forward_now(tk);
 
     /* Make sure the proposed value is valid */
     tmp = timespec64_add(tk_xtime(tk), *ts);
     if (timespec64_compare(&tk->wall_to_monotonic, ts) > 0 ||
         !timespec64_valid_settod(&tmp)) {
         ret = -EINVAL;
         goto error;
     }
 
     tk_xtime_add(tk, ts);
     tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, *ts));
 
 error: /* even if we error out, we forwarded the time, so call update */
     timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);
 
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     /* Signal hrtimers about time change */
     clock_was_set(CLOCK_SET_WALL);
 
     return ret;
 }
 
 /*
  * Indicates if there is an offset between the system clock and the hardware
  * clock/persistent clock/rtc.
  */
 int persistent_clock_is_local;
 
 /*
  * Adjust the time obtained from the CMOS to be UTC time instead of
  * local time.
  *
  * This is ugly, but preferable to the alternatives.  Otherwise we
  * would either need to write a program to do it in /etc/rc (and risk
  * confusion if the program gets run more than once; it would also be
  * hard to make the program warp the clock precisely n hours)  or
  * compile in the timezone information into the kernel.  Bad, bad....
  *
  *                      - TYT, 1992-01-01
  *
  * The best thing to do is to keep the CMOS clock in universal time (UTC)
  * as real UNIX machines always do it. This avoids all headaches about
  * daylight saving times and warping kernel clocks.
  */
 void timekeeping_warp_clock(void)
 {
     if (sys_tz.tz_minuteswest != 0) {
         struct timespec64 adjust;
 
         persistent_clock_is_local = 1;
         adjust.tv_sec = sys_tz.tz_minuteswest * 60;
         adjust.tv_nsec = 0;
         timekeeping_inject_offset(&adjust);
     }
 }
 
 /*
  * __timekeeping_set_tai_offset - Sets the TAI offset from UTC and monotonic
  */
 static void __timekeeping_set_tai_offset(struct timekeeper *tk, s32 tai_offset)
 {
     tk->tai_offset = tai_offset;
     tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tai_offset, 0));
 }
 
 /*
  * change_clocksource - Swaps clocksources if a new one is available
  *
  * Accumulates current time interval and initializes new clocksource
  */
 static int change_clocksource(void *data)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     struct clocksource *new, *old = NULL;
     unsigned long flags;
     bool change = false;
 
     new = (struct clocksource *) data;
 
     /*
      * If the cs is in module, get a module reference. Succeeds
      * for built-in code (owner == NULL) as well.
      */
     if (try_module_get(new->owner)) {
         if (!new->enable || new->enable(new) == 0)
             change = true;
         else
             module_put(new->owner);
     }
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
 
     timekeeping_forward_now(tk);
 
     if (change) {
         old = tk->tkr_mono.clock;
         tk_setup_internals(tk, new);
     }
 
     timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);
 
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     if (old) {
         if (old->disable)
             old->disable(old);
 
         module_put(old->owner);
     }
 
     return 0;
 }
 
 /**
  * timekeeping_notify - Install a new clock source
  * @clock:      pointer to the clock source
  *
  * This function is called from clocksource.c after a new, better clock
  * source has been registered. The caller holds the clocksource_mutex.
  */
 int timekeeping_notify(struct clocksource *clock)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
 
     if (tk->tkr_mono.clock == clock)
         return 0;
     stop_machine(change_clocksource, clock, NULL);
     tick_clock_notify();
     return tk->tkr_mono.clock == clock ? 0 : -1;
 }
 
 /**
  * ktime_get_raw_ts64 - Returns the raw monotonic time in a timespec
  * @ts:     pointer to the timespec64 to be set
  *
  * Returns the raw monotonic time (completely un-modified by ntp)
  */
 void ktime_get_raw_ts64(struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     u64 nsecs;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
         ts->tv_sec = tk->raw_sec;
         nsecs = timekeeping_get_ns(&tk->tkr_raw);
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     ts->tv_nsec = 0;
     timespec64_add_ns(ts, nsecs);
 }
 EXPORT_SYMBOL(ktime_get_raw_ts64);
 
 
 /**
  * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
  */
 int timekeeping_valid_for_hres(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     int ret;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
 
         ret = tk->tkr_mono.clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return ret;
 }
 
 /**
  * timekeeping_max_deferment - Returns max time the clocksource can be deferred
  */
 u64 timekeeping_max_deferment(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     u64 ret;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
 
         ret = tk->tkr_mono.clock->max_idle_ns;
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return ret;
 }
 
 /**
  * read_persistent_clock64 -  Return time from the persistent clock.
  * @ts: Pointer to the storage for the readout value
  *
  * Weak dummy function for arches that do not yet support it.
  * Reads the time from the battery backed persistent clock.
  * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
  *
  *  XXX - Do be sure to remove it once all arches implement it.
  */
 void __weak read_persistent_clock64(struct timespec64 *ts)
 {
     ts->tv_sec = 0;
     ts->tv_nsec = 0;
 }
 
 /**
  * read_persistent_wall_and_boot_offset - Read persistent clock, and also offset
  *                                        from the boot.
  *
  * Weak dummy function for arches that do not yet support it.
  * @wall_time:  - current time as returned by persistent clock
  * @boot_offset: - offset that is defined as wall_time - boot_time
  *
  * The default function calculates offset based on the current value of
  * local_clock(). This way architectures that support sched_clock() but don't
  * support dedicated boot time clock will provide the best estimate of the
  * boot time.
  */
 void __weak __init
 read_persistent_wall_and_boot_offset(struct timespec64 *wall_time,
                      struct timespec64 *boot_offset)
 {
     read_persistent_clock64(wall_time);
     *boot_offset = ns_to_timespec64(local_clock());
 }
 
 /*
  * Flag reflecting whether timekeeping_resume() has injected sleeptime.
  *
  * The flag starts of false and is only set when a suspend reaches
  * timekeeping_suspend(), timekeeping_resume() sets it to false when the
  * timekeeper clocksource is not stopping across suspend and has been
  * used to update sleep time. If the timekeeper clocksource has stopped
  * then the flag stays true and is used by the RTC resume code to decide
  * whether sleeptime must be injected and if so the flag gets false then.
  *
  * If a suspend fails before reaching timekeeping_resume() then the flag
  * stays false and prevents erroneous sleeptime injection.
  */
 static bool suspend_timing_needed;
 
 /* Flag for if there is a persistent clock on this platform */
 static bool persistent_clock_exists;
 
 /*
  * timekeeping_init - Initializes the clocksource and common timekeeping values
  */
 void __init timekeeping_init(void)
 {
     struct timespec64 wall_time, boot_offset, wall_to_mono;
     struct timekeeper *tk = &tk_core.timekeeper;
     struct clocksource *clock;
     unsigned long flags;
 
     read_persistent_wall_and_boot_offset(&wall_time, &boot_offset);
     if (timespec64_valid_settod(&wall_time) &&
         timespec64_to_ns(&wall_time) > 0) {
         persistent_clock_exists = true;
     } else if (timespec64_to_ns(&wall_time) != 0) {
         pr_warn("Persistent clock returned invalid value");
         wall_time = (struct timespec64){0};
     }
 
     if (timespec64_compare(&wall_time, &boot_offset) < 0)
         boot_offset = (struct timespec64){0};
 
     /*
      * We want set wall_to_mono, so the following is true:
      * wall time + wall_to_mono = boot time
      */
     wall_to_mono = timespec64_sub(boot_offset, wall_time);
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
     ntp_init();
 
     clock = clocksource_default_clock();
     if (clock->enable)
         clock->enable(clock);
     tk_setup_internals(tk, clock);
 
     tk_set_xtime(tk, &wall_time);
     tk->raw_sec = 0;
 
     tk_set_wall_to_mono(tk, wall_to_mono);
 
     timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
 
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 }
 
 /* time in seconds when suspend began for persistent clock */
 static struct timespec64 timekeeping_suspend_time;
 
 /**
  * __timekeeping_inject_sleeptime - Internal function to add sleep interval
  * @tk:     Pointer to the timekeeper to be updated
  * @delta:  Pointer to the delta value in timespec64 format
  *
  * Takes a timespec offset measuring a suspend interval and properly
  * adds the sleep offset to the timekeeping variables.
  */
 static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
                        const struct timespec64 *delta)
 {
     if (!timespec64_valid_strict(delta)) {
         printk_deferred(KERN_WARNING
                 "__timekeeping_inject_sleeptime: Invalid "
                 "sleep delta value!\n");
         return;
     }
     tk_xtime_add(tk, delta);
     tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, *delta));
     tk_update_sleep_time(tk, timespec64_to_ktime(*delta));
     tk_debug_account_sleep_time(delta);
 }
 
 #if defined(CONFIG_PM_SLEEP) && defined(CONFIG_RTC_HCTOSYS_DEVICE)
 /**
  * We have three kinds of time sources to use for sleep time
  * injection, the preference order is:
  * 1) non-stop clocksource
  * 2) persistent clock (ie: RTC accessible when irqs are off)
  * 3) RTC
  *
  * 1) and 2) are used by timekeeping, 3) by RTC subsystem.
  * If system has neither 1) nor 2), 3) will be used finally.
  *
  *
  * If timekeeping has injected sleeptime via either 1) or 2),
  * 3) becomes needless, so in this case we don't need to call
  * rtc_resume(), and this is what timekeeping_rtc_skipresume()
  * means.
  */
 bool timekeeping_rtc_skipresume(void)
 {
     return !suspend_timing_needed;
 }
 
 /**
  * 1) can be determined whether to use or not only when doing
  * timekeeping_resume() which is invoked after rtc_suspend(),
  * so we can't skip rtc_suspend() surely if system has 1).
  *
  * But if system has 2), 2) will definitely be used, so in this
  * case we don't need to call rtc_suspend(), and this is what
  * timekeeping_rtc_skipsuspend() means.
  */
 bool timekeeping_rtc_skipsuspend(void)
 {
     return persistent_clock_exists;
 }
 
 /**
  * timekeeping_inject_sleeptime64 - Adds suspend interval to timeekeeping values
  * @delta: pointer to a timespec64 delta value
  *
  * This hook is for architectures that cannot support read_persistent_clock64
  * because their RTC/persistent clock is only accessible when irqs are enabled.
  * and also don't have an effective nonstop clocksource.
  *
  * This function should only be called by rtc_resume(), and allows
  * a suspend offset to be injected into the timekeeping values.
  */
 void timekeeping_inject_sleeptime64(const struct timespec64 *delta)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned long flags;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
 
     suspend_timing_needed = false;
 
     timekeeping_forward_now(tk);
 
     __timekeeping_inject_sleeptime(tk, delta);
 
     timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);
 
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     /* Signal hrtimers about time change */
     clock_was_set(CLOCK_SET_WALL | CLOCK_SET_BOOT);
 }
 #endif
 
 /**
  * timekeeping_resume - Resumes the generic timekeeping subsystem.
  */
 void timekeeping_resume(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     struct clocksource *clock = tk->tkr_mono.clock;
     unsigned long flags;
     struct timespec64 ts_new, ts_delta;
     u64 cycle_now, nsec;
     bool inject_sleeptime = false;
 
     read_persistent_clock64(&ts_new);
 
     clockevents_resume();
     clocksource_resume();
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
 
     /*
      * After system resumes, we need to calculate the suspended time and
      * compensate it for the OS time. There are 3 sources that could be
      * used: Nonstop clocksource during suspend, persistent clock and rtc
      * device.
      *
      * One specific platform may have 1 or 2 or all of them, and the
      * preference will be:
      *  suspend-nonstop clocksource -> persistent clock -> rtc
      * The less preferred source will only be tried if there is no better
      * usable source. The rtc part is handled separately in rtc core code.
      */
     cycle_now = tk_clock_read(&tk->tkr_mono);
     nsec = clocksource_stop_suspend_timing(clock, cycle_now);
     if (nsec > 0) {
         ts_delta = ns_to_timespec64(nsec);
         inject_sleeptime = true;
     } else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
         ts_delta = timespec64_sub(ts_new, timekeeping_suspend_time);
         inject_sleeptime = true;
     }
 
     if (inject_sleeptime) {
         suspend_timing_needed = false;
         __timekeeping_inject_sleeptime(tk, &ts_delta);
     }
 
     /* Re-base the last cycle value */
     tk->tkr_mono.cycle_last = cycle_now;
     tk->tkr_raw.cycle_last  = cycle_now;
 
     tk->ntp_error = 0;
     timekeeping_suspended = 0;
     timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     touch_softlockup_watchdog();
 
     /* Resume the clockevent device(s) and hrtimers */
     tick_resume();
     /* Notify timerfd as resume is equivalent to clock_was_set() */
     timerfd_resume();
 }
 
 int timekeeping_suspend(void)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned long flags;
     struct timespec64       delta, delta_delta;
     static struct timespec64    old_delta;
     struct clocksource *curr_clock;
     u64 cycle_now;
 
     read_persistent_clock64(&timekeeping_suspend_time);
 
     /*
      * On some systems the persistent_clock can not be detected at
      * timekeeping_init by its return value, so if we see a valid
      * value returned, update the persistent_clock_exists flag.
      */
     if (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)
         persistent_clock_exists = true;
 
     suspend_timing_needed = true;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
     timekeeping_forward_now(tk);
     timekeeping_suspended = 1;
 
     /*
      * Since we've called forward_now, cycle_last stores the value
      * just read from the current clocksource. Save this to potentially
      * use in suspend timing.
      */
     curr_clock = tk->tkr_mono.clock;
     cycle_now = tk->tkr_mono.cycle_last;
     clocksource_start_suspend_timing(curr_clock, cycle_now);
 
     if (persistent_clock_exists) {
         /*
          * To avoid drift caused by repeated suspend/resumes,
          * which each can add ~1 second drift error,
          * try to compensate so the difference in system time
          * and persistent_clock time stays close to constant.
          */
         delta = timespec64_sub(tk_xtime(tk), timekeeping_suspend_time);
         delta_delta = timespec64_sub(delta, old_delta);
         if (abs(delta_delta.tv_sec) >= 2) {
             /*
              * if delta_delta is too large, assume time correction
              * has occurred and set old_delta to the current delta.
              */
             old_delta = delta;
         } else {
             /* Otherwise try to adjust old_system to compensate */
             timekeeping_suspend_time =
                 timespec64_add(timekeeping_suspend_time, delta_delta);
         }
     }
 
     timekeeping_update(tk, TK_MIRROR);
     halt_fast_timekeeper(tk);
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     tick_suspend();
     clocksource_suspend();
     clockevents_suspend();
 
     return 0;
 }
 
 /* sysfs resume/suspend bits for timekeeping */
 static struct syscore_ops timekeeping_syscore_ops = {
     .resume     = timekeeping_resume,
     .suspend    = timekeeping_suspend,
 };
 
 static int __init timekeeping_init_ops(void)
 {
     register_syscore_ops(&timekeeping_syscore_ops);
     return 0;
 }
 device_initcall(timekeeping_init_ops);
 
 /*
  * Apply a multiplier adjustment to the timekeeper
  */
 static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk,
                              s64 offset,
                              s32 mult_adj)
 {
     s64 interval = tk->cycle_interval;
 
     if (mult_adj == 0) {
         return;
     } else if (mult_adj == -1) {
         interval = -interval;
         offset = -offset;
     } else if (mult_adj != 1) {
         interval *= mult_adj;
         offset *= mult_adj;
     }
 
     /*
      * So the following can be confusing.
      *
      * To keep things simple, lets assume mult_adj == 1 for now.
      *
      * When mult_adj != 1, remember that the interval and offset values
      * have been appropriately scaled so the math is the same.
      *
      * The basic idea here is that we're increasing the multiplier
      * by one, this causes the xtime_interval to be incremented by
      * one cycle_interval. This is because:
      *  xtime_interval = cycle_interval * mult
      * So if mult is being incremented by one:
      *  xtime_interval = cycle_interval * (mult + 1)
      * Its the same as:
      *  xtime_interval = (cycle_interval * mult) + cycle_interval
      * Which can be shortened to:
      *  xtime_interval += cycle_interval
      *
      * So offset stores the non-accumulated cycles. Thus the current
      * time (in shifted nanoseconds) is:
      *  now = (offset * adj) + xtime_nsec
      * Now, even though we're adjusting the clock frequency, we have
      * to keep time consistent. In other words, we can't jump back
      * in time, and we also want to avoid jumping forward in time.
      *
      * So given the same offset value, we need the time to be the same
      * both before and after the freq adjustment.
      *  now = (offset * adj_1) + xtime_nsec_1
      *  now = (offset * adj_2) + xtime_nsec_2
      * So:
      *  (offset * adj_1) + xtime_nsec_1 =
      *      (offset * adj_2) + xtime_nsec_2
      * And we know:
      *  adj_2 = adj_1 + 1
      * So:
      *  (offset * adj_1) + xtime_nsec_1 =
      *      (offset * (adj_1+1)) + xtime_nsec_2
      *  (offset * adj_1) + xtime_nsec_1 =
      *      (offset * adj_1) + offset + xtime_nsec_2
      * Canceling the sides:
      *  xtime_nsec_1 = offset + xtime_nsec_2
      * Which gives us:
      *  xtime_nsec_2 = xtime_nsec_1 - offset
      * Which simplifies to:
      *  xtime_nsec -= offset
      */
     if ((mult_adj > 0) && (tk->tkr_mono.mult + mult_adj < mult_adj)) {
         /* NTP adjustment caused clocksource mult overflow */
         WARN_ON_ONCE(1);
         return;
     }
 
     tk->tkr_mono.mult += mult_adj;
     tk->xtime_interval += interval;
     tk->tkr_mono.xtime_nsec -= offset;
 }
 
 /*
  * Adjust the timekeeper's multiplier to the correct frequency
  * and also to reduce the accumulated error value.
  */
 static void timekeeping_adjust(struct timekeeper *tk, s64 offset)
 {
     u32 mult;
 
     /*
      * Determine the multiplier from the current NTP tick length.
      * Avoid expensive division when the tick length doesn't change.
      */
     if (likely(tk->ntp_tick == ntp_tick_length())) {
         mult = tk->tkr_mono.mult - tk->ntp_err_mult;
     } else {
         tk->ntp_tick = ntp_tick_length();
         mult = div64_u64((tk->ntp_tick >> tk->ntp_error_shift) -
                  tk->xtime_remainder, tk->cycle_interval);
     }
 
     /*
      * If the clock is behind the NTP time, increase the multiplier by 1
      * to catch up with it. If it's ahead and there was a remainder in the
      * tick division, the clock will slow down. Otherwise it will stay
      * ahead until the tick length changes to a non-divisible value.
      */
     tk->ntp_err_mult = tk->ntp_error > 0 ? 1 : 0;
     mult += tk->ntp_err_mult;
 
     timekeeping_apply_adjustment(tk, offset, mult - tk->tkr_mono.mult);
 
     if (unlikely(tk->tkr_mono.clock->maxadj &&
         (abs(tk->tkr_mono.mult - tk->tkr_mono.clock->mult)
             > tk->tkr_mono.clock->maxadj))) {
         printk_once(KERN_WARNING
             "Adjusting %s more than 11%% (%ld vs %ld)\n",
             tk->tkr_mono.clock->name, (long)tk->tkr_mono.mult,
             (long)tk->tkr_mono.clock->mult + tk->tkr_mono.clock->maxadj);
     }
 
     /*
      * It may be possible that when we entered this function, xtime_nsec
      * was very small.  Further, if we're slightly speeding the clocksource
      * in the code above, its possible the required corrective factor to
      * xtime_nsec could cause it to underflow.
      *
      * Now, since we have already accumulated the second and the NTP
      * subsystem has been notified via second_overflow(), we need to skip
      * the next update.
      */
     if (unlikely((s64)tk->tkr_mono.xtime_nsec < 0)) {
         tk->tkr_mono.xtime_nsec += (u64)NSEC_PER_SEC <<
                             tk->tkr_mono.shift;
         tk->xtime_sec--;
         tk->skip_second_overflow = 1;
     }
 }
 
 /*
  * accumulate_nsecs_to_secs - Accumulates nsecs into secs
  *
  * Helper function that accumulates the nsecs greater than a second
  * from the xtime_nsec field to the xtime_secs field.
  * It also calls into the NTP code to handle leapsecond processing.
  */
 static inline unsigned int accumulate_nsecs_to_secs(struct timekeeper *tk)
 {
     u64 nsecps = (u64)NSEC_PER_SEC << tk->tkr_mono.shift;
     unsigned int clock_set = 0;
 
     while (tk->tkr_mono.xtime_nsec >= nsecps) {
         int leap;
 
         tk->tkr_mono.xtime_nsec -= nsecps;
         tk->xtime_sec++;
 
         /*
          * Skip NTP update if this second was accumulated before,
          * i.e. xtime_nsec underflowed in timekeeping_adjust()
          */
         if (unlikely(tk->skip_second_overflow)) {
             tk->skip_second_overflow = 0;
             continue;
         }
 
         /* Figure out if its a leap sec and apply if needed */
         leap = second_overflow(tk->xtime_sec);
         if (unlikely(leap)) {
             struct timespec64 ts;
 
             tk->xtime_sec += leap;
 
             ts.tv_sec = leap;
             ts.tv_nsec = 0;
             tk_set_wall_to_mono(tk,
                 timespec64_sub(tk->wall_to_monotonic, ts));
 
             __timekeeping_set_tai_offset(tk, tk->tai_offset - leap);
 
             clock_set = TK_CLOCK_WAS_SET;
         }
     }
     return clock_set;
 }
 
 /*
  * logarithmic_accumulation - shifted accumulation of cycles
  *
  * This functions accumulates a shifted interval of cycles into
  * a shifted interval nanoseconds. Allows for O(log) accumulation
  * loop.
  *
  * Returns the unconsumed cycles.
  */
 static u64 logarithmic_accumulation(struct timekeeper *tk, u64 offset,
                     u32 shift, unsigned int *clock_set)
 {
     u64 interval = tk->cycle_interval << shift;
     u64 snsec_per_sec;
 
     /* If the offset is smaller than a shifted interval, do nothing */
     if (offset < interval)
         return offset;
 
     /* Accumulate one shifted interval */
     offset -= interval;
     tk->tkr_mono.cycle_last += interval;
     tk->tkr_raw.cycle_last  += interval;
 
     tk->tkr_mono.xtime_nsec += tk->xtime_interval << shift;
     *clock_set |= accumulate_nsecs_to_secs(tk);
 
     /* Accumulate raw time */
     tk->tkr_raw.xtime_nsec += tk->raw_interval << shift;
     snsec_per_sec = (u64)NSEC_PER_SEC << tk->tkr_raw.shift;
     while (tk->tkr_raw.xtime_nsec >= snsec_per_sec) {
         tk->tkr_raw.xtime_nsec -= snsec_per_sec;
         tk->raw_sec++;
     }
 
     /* Accumulate error between NTP and clock interval */
     tk->ntp_error += tk->ntp_tick << shift;
     tk->ntp_error -= (tk->xtime_interval + tk->xtime_remainder) <<
                         (tk->ntp_error_shift + shift);
 
     return offset;
 }
 
 /*
  * timekeeping_advance - Updates the timekeeper to the current time and
  * current NTP tick length
  */
 static bool timekeeping_advance(enum timekeeping_adv_mode mode)
 {
     struct timekeeper *real_tk = &tk_core.timekeeper;
     struct timekeeper *tk = &shadow_timekeeper;
     u64 offset;
     int shift = 0, maxshift;
     unsigned int clock_set = 0;
     unsigned long flags;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
 
     /* Make sure we're fully resumed: */
     if (unlikely(timekeeping_suspended))
         goto out;
 
     offset = clocksource_delta(tk_clock_read(&tk->tkr_mono),
                    tk->tkr_mono.cycle_last, tk->tkr_mono.mask);
 
     /* Check if there's really nothing to do */
     if (offset < real_tk->cycle_interval && mode == TK_ADV_TICK)
         goto out;
 
     /* Do some additional sanity checking */
     timekeeping_check_update(tk, offset);
 
     /*
      * With NO_HZ we may have to accumulate many cycle_intervals
      * (think "ticks") worth of time at once. To do this efficiently,
      * we calculate the largest doubling multiple of cycle_intervals
      * that is smaller than the offset.  We then accumulate that
      * chunk in one go, and then try to consume the next smaller
      * doubled multiple.
      */
     shift = ilog2(offset) - ilog2(tk->cycle_interval);
     shift = max(0, shift);
     /* Bound shift to one less than what overflows tick_length */
     maxshift = (64 - (ilog2(ntp_tick_length())+1)) - 1;
     shift = min(shift, maxshift);
     while (offset >= tk->cycle_interval) {
         offset = logarithmic_accumulation(tk, offset, shift,
                             &clock_set);
         if (offset < tk->cycle_interval<<shift)
             shift--;
     }
 
     /* Adjust the multiplier to correct NTP error */
     timekeeping_adjust(tk, offset);
 
     /*
      * Finally, make sure that after the rounding
      * xtime_nsec isn't larger than NSEC_PER_SEC
      */
     clock_set |= accumulate_nsecs_to_secs(tk);
 
     write_seqcount_begin(&tk_core.seq);
     /*
      * Update the real timekeeper.
      *
      * We could avoid this memcpy by switching pointers, but that
      * requires changes to all other timekeeper usage sites as
      * well, i.e. move the timekeeper pointer getter into the
      * spinlocked/seqcount protected sections. And we trade this
      * memcpy under the tk_core.seq against one before we start
      * updating.
      */
     timekeeping_update(tk, clock_set);
     memcpy(real_tk, tk, sizeof(*tk));
     /* The memcpy must come last. Do not put anything here! */
     write_seqcount_end(&tk_core.seq);
 out:
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     return !!clock_set;
 }
 
 /**
  * update_wall_time - Uses the current clocksource to increment the wall time
  *
  */
 void update_wall_time(void)
 {
     if (timekeeping_advance(TK_ADV_TICK))
         clock_was_set_delayed();
 }
 
 /**
  * getboottime64 - Return the real time of system boot.
  * @ts:     pointer to the timespec64 to be set
  *
  * Returns the wall-time of boot in a timespec64.
  *
  * This is based on the wall_to_monotonic offset and the total suspend
  * time. Calls to settimeofday will affect the value returned (which
  * basically means that however wrong your real time clock is at boot time,
  * you get the right time here).
  */
 void getboottime64(struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     ktime_t t = ktime_sub(tk->offs_real, tk->offs_boot);
 
     *ts = ktime_to_timespec64(t);
 }
 EXPORT_SYMBOL_GPL(getboottime64);
 
 void ktime_get_coarse_real_ts64(struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
 
         *ts = tk_xtime(tk);
     } while (read_seqcount_retry(&tk_core.seq, seq));
 }
 EXPORT_SYMBOL(ktime_get_coarse_real_ts64);
 
 void ktime_get_coarse_ts64(struct timespec64 *ts)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     struct timespec64 now, mono;
     unsigned int seq;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
 
         now = tk_xtime(tk);
         mono = tk->wall_to_monotonic;
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     set_normalized_timespec64(ts, now.tv_sec + mono.tv_sec,
                 now.tv_nsec + mono.tv_nsec);
 }
 EXPORT_SYMBOL(ktime_get_coarse_ts64);
 
 /*
  * Must hold jiffies_lock
  */
 void do_timer(unsigned long ticks)
 {
     jiffies_64 += ticks;
     calc_global_load();
 }
 
 /**
  * ktime_get_update_offsets_now - hrtimer helper
  * @cwsseq: pointer to check and store the clock was set sequence number
  * @offs_real:  pointer to storage for monotonic -> realtime offset
  * @offs_boot:  pointer to storage for monotonic -> boottime offset
  * @offs_tai:   pointer to storage for monotonic -> clock tai offset
  *
  * Returns current monotonic time and updates the offsets if the
  * sequence number in @cwsseq and timekeeper.clock_was_set_seq are
  * different.
  *
  * Called from hrtimer_interrupt() or retrigger_next_event()
  */
 ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
                      ktime_t *offs_boot, ktime_t *offs_tai)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     unsigned int seq;
     ktime_t base;
     u64 nsecs;
 
     do {
         seq = read_seqcount_begin(&tk_core.seq);
 
         base = tk->tkr_mono.base;
         nsecs = timekeeping_get_ns(&tk->tkr_mono);
         base = ktime_add_ns(base, nsecs);
 
         if (*cwsseq != tk->clock_was_set_seq) {
             *cwsseq = tk->clock_was_set_seq;
             *offs_real = tk->offs_real;
             *offs_boot = tk->offs_boot;
             *offs_tai = tk->offs_tai;
         }
 
         /* Handle leapsecond insertion adjustments */
         if (unlikely(base >= tk->next_leap_ktime))
             *offs_real = ktime_sub(tk->offs_real, ktime_set(1, 0));
 
     } while (read_seqcount_retry(&tk_core.seq, seq));
 
     return base;
 }
 
 /*
  * timekeeping_validate_timex - Ensures the timex is ok for use in do_adjtimex
  */
 static int timekeeping_validate_timex(const struct __kernel_timex *txc)
 {
     if (txc->modes & ADJ_ADJTIME) {
         /* singleshot must not be used with any other mode bits */
         if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
             return -EINVAL;
         if (!(txc->modes & ADJ_OFFSET_READONLY) &&
             !capable(CAP_SYS_TIME))
             return -EPERM;
     } else {
         /* In order to modify anything, you gotta be super-user! */
         if (txc->modes && !capable(CAP_SYS_TIME))
             return -EPERM;
         /*
          * if the quartz is off by more than 10% then
          * something is VERY wrong!
          */
         if (txc->modes & ADJ_TICK &&
             (txc->tick <  900000/USER_HZ ||
              txc->tick > 1100000/USER_HZ))
             return -EINVAL;
     }
 
     if (txc->modes & ADJ_SETOFFSET) {
         /* In order to inject time, you gotta be super-user! */
         if (!capable(CAP_SYS_TIME))
             return -EPERM;
 
         /*
          * Validate if a timespec/timeval used to inject a time
          * offset is valid.  Offsets can be positive or negative, so
          * we don't check tv_sec. The value of the timeval/timespec
          * is the sum of its fields,but *NOTE*:
          * The field tv_usec/tv_nsec must always be non-negative and
          * we can't have more nanoseconds/microseconds than a second.
          */
         if (txc->time.tv_usec < 0)
             return -EINVAL;
 
         if (txc->modes & ADJ_NANO) {
             if (txc->time.tv_usec >= NSEC_PER_SEC)
                 return -EINVAL;
         } else {
             if (txc->time.tv_usec >= USEC_PER_SEC)
                 return -EINVAL;
         }
     }
 
     /*
      * Check for potential multiplication overflows that can
      * only happen on 64-bit systems:
      */
     if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
         if (LLONG_MIN / PPM_SCALE > txc->freq)
             return -EINVAL;
         if (LLONG_MAX / PPM_SCALE < txc->freq)
             return -EINVAL;
     }
 
     return 0;
 }
 
 /**
  * random_get_entropy_fallback - Returns the raw clock source value,
  * used by random.c for platforms with no valid random_get_entropy().
  */
 unsigned long random_get_entropy_fallback(void)
 {
     struct tk_read_base *tkr = &tk_core.timekeeper.tkr_mono;
     struct clocksource *clock = READ_ONCE(tkr->clock);
 
     if (unlikely(timekeeping_suspended || !clock))
         return 0;
     return clock->read(clock);
 }
 EXPORT_SYMBOL_GPL(random_get_entropy_fallback);
 
 /**
  * do_adjtimex() - Accessor function to NTP __do_adjtimex function
  */
 int do_adjtimex(struct __kernel_timex *txc)
 {
     struct timekeeper *tk = &tk_core.timekeeper;
     struct audit_ntp_data ad;
     bool clock_set = false;
     struct timespec64 ts;
     unsigned long flags;
     s32 orig_tai, tai;
     int ret;
 
     /* Validate the data before disabling interrupts */
     ret = timekeeping_validate_timex(txc);
     if (ret)
         return ret;
     add_device_randomness(txc, sizeof(*txc));
 
     if (txc->modes & ADJ_SETOFFSET) {
         struct timespec64 delta;
         delta.tv_sec  = txc->time.tv_sec;
         delta.tv_nsec = txc->time.tv_usec;
         if (!(txc->modes & ADJ_NANO))
             delta.tv_nsec *= 1000;
         ret = timekeeping_inject_offset(&delta);
         if (ret)
             return ret;
 
         audit_tk_injoffset(delta);
     }
 
     audit_ntp_init(&ad);
 
     ktime_get_real_ts64(&ts);
     add_device_randomness(&ts, sizeof(ts));
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
 
     orig_tai = tai = tk->tai_offset;
     ret = __do_adjtimex(txc, &ts, &tai, &ad);
 
     if (tai != orig_tai) {
         __timekeeping_set_tai_offset(tk, tai);
         timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
         clock_set = true;
     }
     tk_update_leap_state(tk);
 
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
     audit_ntp_log(&ad);
 
     /* Update the multiplier immediately if frequency was set directly */
     if (txc->modes & (ADJ_FREQUENCY | ADJ_TICK))
         clock_set |= timekeeping_advance(TK_ADV_FREQ);
 
     if (clock_set)
         clock_was_set(CLOCK_REALTIME);
 
     ntp_notify_cmos_timer();
 
     return ret;
 }
 
 #ifdef CONFIG_NTP_PPS
 /**
  * hardpps() - Accessor function to NTP __hardpps function
  */
 void hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts)
 {
     unsigned long flags;
 
     raw_spin_lock_irqsave(&timekeeper_lock, flags);
     write_seqcount_begin(&tk_core.seq);
 
     __hardpps(phase_ts, raw_ts);
 
     write_seqcount_end(&tk_core.seq);
     raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 }
 EXPORT_SYMBOL(hardpps);
 #endif /* CONFIG_NTP_PPS */

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