/*
 * Copyright 2006 Andi Kleen, SUSE Labs.
 * Subject to the GNU Public License, v.2
 *
 * Fast user context implementation of clock_gettime, gettimeofday, and time.
 *
 * 32 Bit compat layer by Stefani Seibold <stefani@seibold.net>
 *  sponsored by Rohde & Schwarz GmbH & Co. KG Munich/Germany
 *
 * The code should have no internal unresolved relocations.
 * Check with readelf after changing.
 */

#include <uapi/linux/time.h>
#include <asm/vgtod.h>
#include <asm/vvar.h>
#include <asm/unistd.h>
#include <asm/msr.h>
#include <asm/pvclock.h>
#include <asm/mshyperv.h>
#include <linux/math64.h>
#include <linux/time.h>
#include <linux/kernel.h>

#define gtod (&VVAR(vsyscall_gtod_data))

extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts);
extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
extern time_t __vdso_time(time_t *t);

#ifdef CONFIG_PARAVIRT_CLOCK
extern u8 pvclock_page
        __attribute__((visibility("hidden")));
#endif

#ifdef CONFIG_HYPERV_TSCPAGE
extern u8 hvclock_page
        __attribute__((visibility("hidden")));
#endif

#ifndef BUILD_VDSO32

notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
        long ret;
        asm("syscall" : "=a" (ret) :
            "0" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory");
        return ret;
}

notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
{
        long ret;

        asm("syscall" : "=a" (ret) :
            "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
        return ret;
}


#else

notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
        long ret;

        asm(
                "mov %%ebx, %%edx \n"
                "mov %2, %%ebx \n"
                "call __kernel_vsyscall \n"
                "mov %%edx, %%ebx \n"
                : "=a" (ret)
                : "0" (__NR_clock_gettime), "g" (clock), "c" (ts)
                : "memory", "edx");
        return ret;
}

notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
{
        long ret;

        asm(
                "mov %%ebx, %%edx \n"
                "mov %2, %%ebx \n"
                "call __kernel_vsyscall \n"
                "mov %%edx, %%ebx \n"
                : "=a" (ret)
                : "0" (__NR_gettimeofday), "g" (tv), "c" (tz)
                : "memory", "edx");
        return ret;
}

#endif

#ifdef CONFIG_PARAVIRT_CLOCK
static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void)
{
        return (const struct pvclock_vsyscall_time_info *)&pvclock_page;
}

static notrace u64 vread_pvclock(int *mode)
{
        const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
        u64 ret;
        u64 last;
        u32 version;

        /*
         * Note: The kernel and hypervisor must guarantee that cpu ID
         * number maps 1:1 to per-CPU pvclock time info.
         *
         * Because the hypervisor is entirely unaware of guest userspace
         * preemption, it cannot guarantee that per-CPU pvclock time
         * info is updated if the underlying CPU changes or that that
         * version is increased whenever underlying CPU changes.
         *
         * On KVM, we are guaranteed that pvti updates for any vCPU are
         * atomic as seen by *all* vCPUs.  This is an even stronger
         * guarantee than we get with a normal seqlock.
         *
         * On Xen, we don't appear to have that guarantee, but Xen still
         * supplies a valid seqlock using the version field.
         *
         * We only do pvclock vdso timing at all if
         * PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
         * mean that all vCPUs have matching pvti and that the TSC is
         * synced, so we can just look at vCPU 0's pvti.
         */

        do {
                version = pvclock_read_begin(pvti);

                if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))) {
                        *mode = VCLOCK_NONE;
                        return 0;
                }

                ret = __pvclock_read_cycles(pvti, rdtsc_ordered());
        } while (pvclock_read_retry(pvti, version));

        /* refer to vread_tsc() comment for rationale */
        last = gtod->cycle_last;

        if (likely(ret >= last))
                return ret;

        return last;
}
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
static notrace u64 vread_hvclock(int *mode)
{
        const struct ms_hyperv_tsc_page *tsc_pg =
                (const struct ms_hyperv_tsc_page *)&hvclock_page;
        u64 current_tick = hv_read_tsc_page(tsc_pg);

        if (current_tick != U64_MAX)
                return current_tick;

        *mode = VCLOCK_NONE;
        return 0;
}
#endif

notrace static u64 vread_tsc(void)
{
        u64 ret = (u64)rdtsc_ordered();
        u64 last = gtod->cycle_last;

        if (likely(ret >= last))
                return ret;

        /*
         * GCC likes to generate cmov here, but this branch is extremely
         * predictable (it's just a function of time and the likely is
         * very likely) and there's a data dependence, so force GCC
         * to generate a branch instead.  I don't barrier() because
         * we don't actually need a barrier, and if this function
         * ever gets inlined it will generate worse code.
         */
        asm volatile ("");
        return last;
}

notrace static inline u64 vgetsns(int *mode)
{
        u64 v;
        cycles_t cycles;

        if (gtod->vclock_mode == VCLOCK_TSC)
                cycles = vread_tsc();
#ifdef CONFIG_PARAVIRT_CLOCK
        else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
                cycles = vread_pvclock(mode);
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
        else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
                cycles = vread_hvclock(mode);
#endif
        else
                return 0;
        v = (cycles - gtod->cycle_last) & gtod->mask;
        return v * gtod->mult;
}

/* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
notrace static int __always_inline do_realtime(struct timespec *ts)
{
        unsigned long seq;
        u64 ns;
        int mode;

        do {
                seq = gtod_read_begin(gtod);
                mode = gtod->vclock_mode;
                ts->tv_sec = gtod->wall_time_sec;
                ns = gtod->wall_time_snsec;
                ns += vgetsns(&mode);
                ns >>= gtod->shift;
        } while (unlikely(gtod_read_retry(gtod, seq)));

        ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
        ts->tv_nsec = ns;

        return mode;
}

notrace static int __always_inline do_monotonic(struct timespec *ts)
{
        unsigned long seq;
        u64 ns;
        int mode;

        do {
                seq = gtod_read_begin(gtod);
                mode = gtod->vclock_mode;
                ts->tv_sec = gtod->monotonic_time_sec;
                ns = gtod->monotonic_time_snsec;
                ns += vgetsns(&mode);
                ns >>= gtod->shift;
        } while (unlikely(gtod_read_retry(gtod, seq)));

        ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
        ts->tv_nsec = ns;

        return mode;
}

notrace static void do_realtime_coarse(struct timespec *ts)
{
        unsigned long seq;
        do {
                seq = gtod_read_begin(gtod);
                ts->tv_sec = gtod->wall_time_coarse_sec;
                ts->tv_nsec = gtod->wall_time_coarse_nsec;
        } while (unlikely(gtod_read_retry(gtod, seq)));
}

notrace static void do_monotonic_coarse(struct timespec *ts)
{
        unsigned long seq;
        do {
                seq = gtod_read_begin(gtod);
                ts->tv_sec = gtod->monotonic_time_coarse_sec;
                ts->tv_nsec = gtod->monotonic_time_coarse_nsec;
        } while (unlikely(gtod_read_retry(gtod, seq)));
}

notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
        switch (clock) {
        case CLOCK_REALTIME:
                if (do_realtime(ts) == VCLOCK_NONE)
                        goto fallback;
                break;
        case CLOCK_MONOTONIC:
                if (do_monotonic(ts) == VCLOCK_NONE)
                        goto fallback;
                break;
        case CLOCK_REALTIME_COARSE:
                do_realtime_coarse(ts);
                break;
        case CLOCK_MONOTONIC_COARSE:
                do_monotonic_coarse(ts);
                break;
        default:
                goto fallback;
        }

        return 0;
fallback:
        return vdso_fallback_gettime(clock, ts);
}
int clock_gettime(clockid_t, struct timespec *)
        __attribute__((weak, alias("__vdso_clock_gettime")));

notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
{
        if (likely(tv != NULL)) {
                if (unlikely(do_realtime((struct timespec *)tv) == VCLOCK_NONE))
                        return vdso_fallback_gtod(tv, tz);
                tv->tv_usec /= 1000;
        }
        if (unlikely(tz != NULL)) {
                tz->tz_minuteswest = gtod->tz_minuteswest;
                tz->tz_dsttime = gtod->tz_dsttime;
        }

        return 0;
}
int gettimeofday(struct timeval *, struct timezone *)
        __attribute__((weak, alias("__vdso_gettimeofday")));

/*
 * This will break when the xtime seconds get inaccurate, but that is
 * unlikely
 */
notrace time_t __vdso_time(time_t *t)
{
        /* This is atomic on x86 so we don't need any locks. */
        time_t result = READ_ONCE(gtod->wall_time_sec);

        if (t)
                *t = result;
        return result;
}
time_t time(time_t *t)
        __attribute__((weak, alias("__vdso_time")));