// SPDX-License-Identifier: GPL-2.0-or-later
/*  paravirtual clock -- common code used by kvm/xen

*/

#include <linux/clocksource.h>
#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/sched.h>
#include <linux/gfp.h>
#include <linux/memblock.h>
#include <linux/nmi.h>

#include <asm/fixmap.h>
#include <asm/pvclock.h>
#include <asm/vgtod.h>

static u8 valid_flags __read_mostly = 0;
static struct pvclock_vsyscall_time_info *pvti_cpu0_va __read_mostly;

void pvclock_set_flags(u8 flags)
{
        valid_flags = flags;
}

unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
{
        u64 pv_tsc_khz = 1000000ULL << 32;

        do_div(pv_tsc_khz, src->tsc_to_system_mul);
        if (src->tsc_shift < 0)
                pv_tsc_khz <<= -src->tsc_shift;
        else
                pv_tsc_khz >>= src->tsc_shift;
        return pv_tsc_khz;
}

void pvclock_touch_watchdogs(void)
{
        touch_softlockup_watchdog_sync();
        clocksource_touch_watchdog();
        rcu_cpu_stall_reset();
        reset_hung_task_detector();
}

static atomic64_t last_value = ATOMIC64_INIT(0);

void pvclock_resume(void)
{
        atomic64_set(&last_value, 0);
}

u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
{
        unsigned version;
        u8 flags;

        do {
                version = pvclock_read_begin(src);
                flags = src->flags;
        } while (pvclock_read_retry(src, version));

        return flags & valid_flags;
}

static __always_inline
u64 __pvclock_clocksource_read(struct pvclock_vcpu_time_info *src, bool dowd)
{
        unsigned version;
        u64 ret;
        u64 last;
        u8 flags;

        do {
                version = pvclock_read_begin(src);
                ret = __pvclock_read_cycles(src, rdtsc_ordered());
                flags = src->flags;
        } while (pvclock_read_retry(src, version));

        if (dowd && unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
                src->flags &= ~PVCLOCK_GUEST_STOPPED;
                pvclock_touch_watchdogs();
        }

        if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
                (flags & PVCLOCK_TSC_STABLE_BIT))
                return ret;

        /*
         * Assumption here is that last_value, a global accumulator, always goes
         * forward. If we are less than that, we should not be much smaller.
         * We assume there is an error margin we're inside, and then the correction
         * does not sacrifice accuracy.
         *
         * For reads: global may have changed between test and return,
         * but this means someone else updated poked the clock at a later time.
         * We just need to make sure we are not seeing a backwards event.
         *
         * For updates: last_value = ret is not enough, since two vcpus could be
         * updating at the same time, and one of them could be slightly behind,
         * making the assumption that last_value always go forward fail to hold.
         */
        last = raw_atomic64_read(&last_value);
        do {
                if (ret <= last)
                        return last;
        } while (!raw_atomic64_try_cmpxchg(&last_value, &last, ret));

        return ret;
}

u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
{
        return __pvclock_clocksource_read(src, true);
}

noinstr u64 pvclock_clocksource_read_nowd(struct pvclock_vcpu_time_info *src)
{
        return __pvclock_clocksource_read(src, false);
}

void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
                            struct pvclock_vcpu_time_info *vcpu_time,
                            struct timespec64 *ts)
{
        u32 version;
        u64 delta;
        struct timespec64 now;

        /* get wallclock at system boot */
        do {
                version = wall_clock->version;
                rmb();          /* fetch version before time */
                /*
                 * Note: wall_clock->sec is a u32 value, so it can
                 * only store dates between 1970 and 2106. To allow
                 * times beyond that, we need to create a new hypercall
                 * interface with an extended pvclock_wall_clock structure
                 * like ARM has.
                 */
                now.tv_sec  = wall_clock->sec;
                now.tv_nsec = wall_clock->nsec;
                rmb();          /* fetch time before checking version */
        } while ((wall_clock->version & 1) || (version != wall_clock->version));

        delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
        delta += now.tv_sec * NSEC_PER_SEC + now.tv_nsec;

        now.tv_nsec = do_div(delta, NSEC_PER_SEC);
        now.tv_sec = delta;

        set_normalized_timespec64(ts, now.tv_sec, now.tv_nsec);
}

void pvclock_set_pvti_cpu0_va(struct pvclock_vsyscall_time_info *pvti)
{
        WARN_ON(vclock_was_used(VDSO_CLOCKMODE_PVCLOCK));
        pvti_cpu0_va = pvti;
}

struct pvclock_vsyscall_time_info *pvclock_get_pvti_cpu0_va(void)
{
        return pvti_cpu0_va;
}
EXPORT_SYMBOL_GPL(pvclock_get_pvti_cpu0_va);