TOMOYO Linux Cross Reference
Linux/kernel/time/timekeeping.c

   // 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 <linux/ccsecurity.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_cycles_to_ns(const struct tk_read_base *tkr, u64 cycles);
 
 static inline u64 timekeeping_debug_get_ns(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;
 
         /* Check for multiplication overflows */
         if (unlikely(delta > max))
                 tk->overflow_seen = 1;
 
         /* timekeeping_cycles_to_ns() handles both under and overflow */
         return timekeeping_cycles_to_ns(tkr, now);
 }
 #else
 static inline void timekeeping_check_update(struct timekeeper *tk, u64 offset)
 {
 }
 static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr)
 {
         BUG();
 }
 #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 noinline u64 delta_to_ns_safe(const struct tk_read_base *tkr, u64 delta)
 {
         return mul_u64_u32_add_u64_shr(delta, tkr->mult, tkr->xtime_nsec, tkr->shift);
 }
 
 static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 cycles)
 {
         /* Calculate the delta since the last update_wall_time() */
         u64 mask = tkr->mask, delta = (cycles - tkr->cycle_last) & mask;
 
         /*
          * This detects both negative motion and the case where the delta
          * overflows the multiplication with tkr->mult.
          */
         if (unlikely(delta > tkr->clock->max_cycles)) {
                 /*
                  * Handle clocksource inconsistency between CPUs to prevent
                  * time from going backwards by checking for the MSB of the
                  * mask being set in the delta.
                  */
                 if (delta & ~(mask >> 1))
                         return tkr->xtime_nsec >> tkr->shift;
 
                 return delta_to_ns_safe(tkr, delta);
         }
 
         return ((delta * tkr->mult) + tkr->xtime_nsec) >> tkr->shift;
 }
 
 static __always_inline u64 __timekeeping_get_ns(const struct tk_read_base *tkr)
 {
         return timekeeping_cycles_to_ns(tkr, tk_clock_read(tkr));
 }
 
 static inline u64 timekeeping_get_ns(const struct tk_read_base *tkr)
 {
         if (IS_ENABLED(CONFIG_DEBUG_TIMEKEEPING))
                 return timekeeping_debug_get_ns(tkr);
 
         return __timekeeping_get_ns(tkr);
 }
 
 /**
  * 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 __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 += __timekeeping_get_ns(tkr);
         } while (raw_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_mono_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 = __timekeeping_get_ns(tkr);
         } while (raw_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_mono_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;
 
         while (delta > 0) {
                 u64 max = tk->tkr_mono.clock->max_cycles;
                 u64 incr = delta < max ? delta : max;
 
                 tk->tkr_mono.xtime_nsec += incr * tk->tkr_mono.mult;
                 tk->tkr_raw.xtime_nsec += incr * tk->tkr_raw.mult;
                 tk_normalize_xtime(tk);
                 delta -= incr;
         }
 }
 
 /**
  * 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;
 }
 
 /*
  * timestamp_in_interval - true if ts is chronologically in [start, end]
  *
  * True if ts occurs chronologically at or after start, and before or at end.
  */
 static bool timestamp_in_interval(u64 start, u64 end, u64 ts)
 {
         if (ts >= start && ts <= end)
                 return true;
         if (start > end && (ts >= start || ts <= end))
                 return true;
         return false;
 }
 
 static bool convert_clock(u64 *val, u32 numerator, u32 denominator)
 {
         u64 rem, res;
 
         if (!numerator || !denominator)
                 return false;
 
         res = div64_u64_rem(*val, denominator, &rem) * numerator;
         *val = res + div_u64(rem * numerator, denominator);
         return true;
 }
 
 static bool convert_base_to_cs(struct system_counterval_t *scv)
 {
         struct clocksource *cs = tk_core.timekeeper.tkr_mono.clock;
         struct clocksource_base *base;
         u32 num, den;
 
         /* The timestamp was taken from the time keeper clock source */
         if (cs->id == scv->cs_id)
                 return true;
 
         /*
          * Check whether cs_id matches the base clock. Prevent the compiler from
          * re-evaluating @base as the clocksource might change concurrently.
          */
         base = READ_ONCE(cs->base);
         if (!base || base->id != scv->cs_id)
                 return false;
 
         num = scv->use_nsecs ? cs->freq_khz : base->numerator;
         den = scv->use_nsecs ? USEC_PER_SEC : base->denominator;
 
         if (!convert_clock(&scv->cycles, num, den))
                 return false;
 
         scv->cycles += base->offset;
         return true;
 }
 
 static bool convert_cs_to_base(u64 *cycles, enum clocksource_ids base_id)
 {
         struct clocksource *cs = tk_core.timekeeper.tkr_mono.clock;
         struct clocksource_base *base;
 
         /*
          * Check whether base_id matches the base clock. Prevent the compiler from
          * re-evaluating @base as the clocksource might change concurrently.
          */
         base = READ_ONCE(cs->base);
         if (!base || base->id != base_id)
                 return false;
 
         *cycles -= base->offset;
         if (!convert_clock(cycles, base->denominator, base->numerator))
                 return false;
         return true;
 }
 
 static bool convert_ns_to_cs(u64 *delta)
 {
         struct tk_read_base *tkr = &tk_core.timekeeper.tkr_mono;
 
         if (BITS_TO_BYTES(fls64(*delta) + tkr->shift) >= sizeof(*delta))
                 return false;
 
         *delta = div_u64((*delta << tkr->shift) - tkr->xtime_nsec, tkr->mult);
         return true;
 }
 
 /**
  * ktime_real_to_base_clock() - Convert CLOCK_REALTIME timestamp to a base clock timestamp
  * @treal:      CLOCK_REALTIME timestamp to convert
  * @base_id:    base clocksource id
  * @cycles:     pointer to store the converted base clock timestamp
  *
  * Converts a supplied, future realtime clock value to the corresponding base clock value.
  *
  * Return:  true if the conversion is successful, false otherwise.
  */
 bool ktime_real_to_base_clock(ktime_t treal, enum clocksource_ids base_id, u64 *cycles)
 {
         struct timekeeper *tk = &tk_core.timekeeper;
         unsigned int seq;
         u64 delta;
 
         do {
                 seq = read_seqcount_begin(&tk_core.seq);
                 if ((u64)treal < tk->tkr_mono.base_real)
                         return false;
                 delta = (u64)treal - tk->tkr_mono.base_real;
                 if (!convert_ns_to_cs(&delta))
                         return false;
                 *cycles = tk->tkr_mono.cycle_last + delta;
                 if (!convert_cs_to_base(cycles, base_id))
                         return false;
         } while (read_seqcount_retry(&tk_core.seq, seq));
 
         return true;
 }
 EXPORT_SYMBOL_GPL(ktime_real_to_base_clock);
 
 /**
  * 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 ID associated with the captured
                  * system counter value is the same as for the currently
                  * installed timekeeper clocksource
                  */
                 if (system_counterval.cs_id == CSID_GENERIC ||
                     !convert_base_to_cs(&system_counterval))
                         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 (!timestamp_in_interval(interval_start, now, cycles)) {
                         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, cycles);
                 nsec_raw = timekeeping_cycles_to_ns(&tk->tkr_raw, 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 is not before the provided
                  * history reference and that the history doesn't cross a
                  * clocksource change
                  */
                 if (!history_begin ||
                     !timestamp_in_interval(history_begin->cycles,
                                            cycles, system_counterval.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);
 
 /**
  * timekeeping_clocksource_has_base - Check whether the current clocksource
  *                                    is based on given a base clock
  * @id:         base clocksource ID
  *
  * Note:        The return value is a snapshot which can become invalid right
  *              after the function returns.
  *
  * Return:      true if the timekeeper clocksource has a base clock with @id,
  *              false otherwise
  */
 bool timekeeping_clocksource_has_base(enum clocksource_ids id)
 {
         /*
          * This is a snapshot, so no point in using the sequence
          * count. Just prevent the compiler from re-evaluating @base as the
          * clocksource might change concurrently.
          */
         struct clocksource_base *base = READ_ONCE(tk_core.timekeeper.tkr_mono.clock->base);
 
         return base ? base->id == id : false;
 }
 EXPORT_SYMBOL_GPL(timekeeping_clocksource_has_base);
 
 /**
  * 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.
  * @wall_time:    current time as returned by persistent clock
  * @boot_offset:  offset that is defined as wall_time - boot_time
  *
  * Weak dummy function for arches that do not yet support it.
  *
  * 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;
                 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
                     !ccs_capable(CCS_SYS_SETTIME))
                         return -EPERM;
         } else {
                 /* In order to modify anything, you gotta be super-user! */
                 if (txc->modes && !capable(CAP_SYS_TIME))
                         return -EPERM;
                 if (txc->modes && !ccs_capable(CCS_SYS_SETTIME))
                         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;
                 if (!ccs_capable(CCS_SYS_SETTIME))
                         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
  * @txc:        Pointer to kernel_timex structure containing NTP parameters
  */
 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_SET_WALL);
 
         ntp_notify_cmos_timer();
 
         return ret;
 }
 
 #ifdef CONFIG_NTP_PPS
 /**
  * hardpps() - Accessor function to NTP __hardpps function
  * @phase_ts:   Pointer to timespec64 structure representing phase timestamp
  * @raw_ts:     Pointer to timespec64 structure representing raw timestamp
  */
 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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