crypto: akcipher - Drop sign/verify operations

[linux.git] / 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 "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;
        } else {
                /* In order to modify anything, you gotta be super-user! */
                if (txc->modes && !capable(CAP_SYS_TIME))
                        return -EPERM;
                /*
                 * if the quartz is off by more than 10% then
                 * something is VERY wrong!
                 */
                if (txc->modes & ADJ_TICK &&
                    (txc->tick <  900000/USER_HZ ||
                     txc->tick > 1100000/USER_HZ))
                        return -EINVAL;
        }

        if (txc->modes & ADJ_SETOFFSET) {
                /* In order to inject time, you gotta be super-user! */
                if (!capable(CAP_SYS_TIME))
                        return -EPERM;

                /*
                 * Validate if a timespec/timeval used to inject a time
                 * offset is valid.  Offsets can be positive or negative, so
                 * we don't check tv_sec. The value of the timeval/timespec
                 * is the sum of its fields,but *NOTE*:
                 * The field tv_usec/tv_nsec must always be non-negative and
                 * we can't have more nanoseconds/microseconds than a second.
                 */
                if (txc->time.tv_usec < 0)
                        return -EINVAL;

                if (txc->modes & ADJ_NANO) {
                        if (txc->time.tv_usec >= NSEC_PER_SEC)
                                return -EINVAL;
                } else {
                        if (txc->time.tv_usec >= USEC_PER_SEC)
                                return -EINVAL;
                }
        }

        /*
         * Check for potential multiplication overflows that can
         * only happen on 64-bit systems:
         */
        if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
                if (LLONG_MIN / PPM_SCALE > txc->freq)
                        return -EINVAL;
                if (LLONG_MAX / PPM_SCALE < txc->freq)
                        return -EINVAL;
        }

        return 0;
}

/**
 * random_get_entropy_fallback - Returns the raw clock source value,
 * used by random.c for platforms with no valid random_get_entropy().
 */
unsigned long random_get_entropy_fallback(void)
{
        struct tk_read_base *tkr = &tk_core.timekeeper.tkr_mono;
        struct clocksource *clock = READ_ONCE(tkr->clock);

        if (unlikely(timekeeping_suspended || !clock))
                return 0;
        return clock->read(clock);
}
EXPORT_SYMBOL_GPL(random_get_entropy_fallback);

/**
 * do_adjtimex() - Accessor function to NTP __do_adjtimex function
 * @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 offset_set = false;
        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;

                offset_set = delta.tv_sec != 0;
                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(offset_set);

        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 */