// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
 * Copyright (C) 2012-2014 Cisco Systems
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Copyright (C) 2019 Intel Corporation
 */

#include <linux/clockchips.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/jiffies.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <asm/irq.h>
#include <asm/param.h>
#include <kern_util.h>
#include <os.h>
#include <linux/delay.h>
#include <linux/time-internal.h>
#include <linux/um_timetravel.h>
#include <shared/init.h>

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
#include <linux/sched/clock.h>

enum time_travel_mode time_travel_mode;
EXPORT_SYMBOL_GPL(time_travel_mode);

static bool time_travel_start_set;
static unsigned long long time_travel_start;
static unsigned long long time_travel_time;
static unsigned long long time_travel_shm_offset;
static LIST_HEAD(time_travel_events);
static LIST_HEAD(time_travel_irqs);
static unsigned long long time_travel_timer_interval;
static unsigned long long time_travel_next_event;
static struct time_travel_event time_travel_timer_event;
static int time_travel_ext_fd = -1;
static unsigned int time_travel_ext_waiting;
static bool time_travel_ext_prev_request_valid;
static unsigned long long time_travel_ext_prev_request;
static unsigned long long *time_travel_ext_free_until;
static unsigned long long _time_travel_ext_free_until;
static u16 time_travel_shm_id;
static struct um_timetravel_schedshm *time_travel_shm;
static union um_timetravel_schedshm_client *time_travel_shm_client;

unsigned long tt_extra_sched_jiffies;

notrace unsigned long long sched_clock(void)
{
        return (unsigned long long)(jiffies - INITIAL_JIFFIES +
                                    tt_extra_sched_jiffies)
                                        * (NSEC_PER_SEC / HZ);
}

static void time_travel_set_time(unsigned long long ns)
{
        if (unlikely(ns < time_travel_time))
                panic("time-travel: time goes backwards %lld -> %lld\n",
                      time_travel_time, ns);
        else if (unlikely(ns >= S64_MAX))
                panic("The system was going to sleep forever, aborting");

        time_travel_time = ns;
}

enum time_travel_message_handling {
        TTMH_IDLE,
        TTMH_POLL,
        TTMH_READ,
        TTMH_READ_START_ACK,
};

static u64 bc_message;
int time_travel_should_print_bc_msg;

void _time_travel_print_bc_msg(void)
{
        time_travel_should_print_bc_msg = 0;
        printk(KERN_INFO "time-travel: received broadcast 0x%llx\n", bc_message);
}

static void time_travel_setup_shm(int fd, u16 id)
{
        u32 len;

        time_travel_shm = os_mmap_rw_shared(fd, sizeof(*time_travel_shm));

        if (!time_travel_shm)
                goto out;

        len = time_travel_shm->len;

        if (time_travel_shm->version != UM_TIMETRAVEL_SCHEDSHM_VERSION ||
            len < struct_size(time_travel_shm, clients, id + 1)) {
                os_unmap_memory(time_travel_shm, sizeof(*time_travel_shm));
                time_travel_shm = NULL;
                goto out;
        }

        time_travel_shm = os_mremap_rw_shared(time_travel_shm,
                                              sizeof(*time_travel_shm),
                                              len);
        if (!time_travel_shm)
                goto out;

        time_travel_shm_offset = time_travel_shm->current_time;
        time_travel_shm_client = &time_travel_shm->clients[id];
        time_travel_shm_client->capa |= UM_TIMETRAVEL_SCHEDSHM_CAP_TIME_SHARE;
        time_travel_shm_id = id;
        /* always look at that free_until from now on */
        time_travel_ext_free_until = &time_travel_shm->free_until;
out:
        os_close_file(fd);
}

static void time_travel_handle_message(struct um_timetravel_msg *msg,
                                       enum time_travel_message_handling mode)
{
        struct um_timetravel_msg resp = {
                .op = UM_TIMETRAVEL_ACK,
        };
        int ret;

        /*
         * We can't unlock here, but interrupt signals with a timetravel_handler
         * (see um_request_irq_tt) get to the timetravel_handler anyway.
         */
        if (mode != TTMH_READ) {
                BUG_ON(mode == TTMH_IDLE && !irqs_disabled());

                while (os_poll(1, &time_travel_ext_fd) != 0) {
                        /* nothing */
                }
        }

        if (unlikely(mode == TTMH_READ_START_ACK)) {
                int fd[UM_TIMETRAVEL_SHARED_MAX_FDS];

                ret = os_rcv_fd_msg(time_travel_ext_fd, fd,
                                    ARRAY_SIZE(fd), msg, sizeof(*msg));
                if (ret == sizeof(*msg)) {
                        time_travel_setup_shm(fd[UM_TIMETRAVEL_SHARED_MEMFD],
                                              msg->time & UM_TIMETRAVEL_START_ACK_ID);
                        /* we don't use the logging for now */
                        os_close_file(fd[UM_TIMETRAVEL_SHARED_LOGFD]);
                }
        } else {
                ret = os_read_file(time_travel_ext_fd, msg, sizeof(*msg));
        }

        if (ret == 0)
                panic("time-travel external link is broken\n");
        if (ret != sizeof(*msg))
                panic("invalid time-travel message - %d bytes\n", ret);

        switch (msg->op) {
        default:
                WARN_ONCE(1, "time-travel: unexpected message %lld\n",
                          (unsigned long long)msg->op);
                break;
        case UM_TIMETRAVEL_ACK:
                return;
        case UM_TIMETRAVEL_RUN:
                time_travel_set_time(msg->time);
                if (time_travel_shm) {
                        /* no request right now since we're running */
                        time_travel_shm_client->flags &=
                                ~UM_TIMETRAVEL_SCHEDSHM_FLAGS_REQ_RUN;
                        /* no ack for shared memory RUN */
                        return;
                }
                break;
        case UM_TIMETRAVEL_FREE_UNTIL:
                /* not supposed to get this with shm, but ignore it */
                if (time_travel_shm)
                        break;
                time_travel_ext_free_until = &_time_travel_ext_free_until;
                _time_travel_ext_free_until = msg->time;
                break;
        case UM_TIMETRAVEL_BROADCAST:
                bc_message = msg->time;
                time_travel_should_print_bc_msg = 1;
                break;
        }

        resp.seq = msg->seq;
        os_write_file(time_travel_ext_fd, &resp, sizeof(resp));
}

static u64 time_travel_ext_req(u32 op, u64 time)
{
        static int seq;
        int mseq = ++seq;
        struct um_timetravel_msg msg = {
                .op = op,
                .time = time,
                .seq = mseq,
        };

        /*
         * We need to block even the timetravel handlers of SIGIO here and
         * only restore their use when we got the ACK - otherwise we may
         * (will) get interrupted by that, try to queue the IRQ for future
         * processing and thus send another request while we're still waiting
         * for an ACK, but the peer doesn't know we got interrupted and will
         * send the ACKs in the same order as the message, but we'd need to
         * see them in the opposite order ...
         *
         * This wouldn't matter *too* much, but some ACKs carry the
         * current time (for UM_TIMETRAVEL_GET) and getting another
         * ACK without a time would confuse us a lot!
         *
         * The sequence number assignment that happens here lets us
         * debug such message handling issues more easily.
         */
        block_signals_hard();
        os_write_file(time_travel_ext_fd, &msg, sizeof(msg));

        /* no ACK expected for WAIT in shared memory mode */
        if (msg.op == UM_TIMETRAVEL_WAIT && time_travel_shm)
                goto done;

        while (msg.op != UM_TIMETRAVEL_ACK)
                time_travel_handle_message(&msg,
                                           op == UM_TIMETRAVEL_START ?
                                                TTMH_READ_START_ACK :
                                                TTMH_READ);

        if (msg.seq != mseq)
                panic("time-travel: ACK message has different seqno! op=%d, seq=%d != %d time=%lld\n",
                      msg.op, msg.seq, mseq, msg.time);

        if (op == UM_TIMETRAVEL_GET)
                time_travel_set_time(msg.time);
done:
        unblock_signals_hard();

        return msg.time;
}

void __time_travel_wait_readable(int fd)
{
        int fds[2] = { fd, time_travel_ext_fd };
        int ret;

        if (time_travel_mode != TT_MODE_EXTERNAL)
                return;

        while ((ret = os_poll(2, fds))) {
                struct um_timetravel_msg msg;

                if (ret == 1)
                        time_travel_handle_message(&msg, TTMH_READ);
        }
}
EXPORT_SYMBOL_GPL(__time_travel_wait_readable);

static void time_travel_ext_update_request(unsigned long long time)
{
        if (time_travel_mode != TT_MODE_EXTERNAL)
                return;

        /* asked for exactly this time previously */
        if (time_travel_ext_prev_request_valid &&
            time == time_travel_ext_prev_request)
                return;

        /*
         * if we're running and are allowed to run past the request
         * then we don't need to update it either
         *
         * Note for shm we ignore FREE_UNTIL messages and leave the pointer
         * to shared memory, and for non-shm the offset is 0.
         */
        if (!time_travel_ext_waiting && time_travel_ext_free_until &&
            time < (*time_travel_ext_free_until - time_travel_shm_offset))
                return;

        time_travel_ext_prev_request = time;
        time_travel_ext_prev_request_valid = true;

        if (time_travel_shm) {
                union um_timetravel_schedshm_client *running;

                running = &time_travel_shm->clients[time_travel_shm->running_id];

                if (running->capa & UM_TIMETRAVEL_SCHEDSHM_CAP_TIME_SHARE) {
                        time_travel_shm_client->flags |=
                                UM_TIMETRAVEL_SCHEDSHM_FLAGS_REQ_RUN;
                        time += time_travel_shm_offset;
                        time_travel_shm_client->req_time = time;
                        if (time < time_travel_shm->free_until)
                                time_travel_shm->free_until = time;
                        return;
                }
        }

        time_travel_ext_req(UM_TIMETRAVEL_REQUEST, time);
}

void __time_travel_propagate_time(void)
{
        static unsigned long long last_propagated;

        if (time_travel_shm) {
                if (time_travel_shm->running_id != time_travel_shm_id)
                        panic("time-travel: setting time while not running\n");
                time_travel_shm->current_time = time_travel_time +
                                                time_travel_shm_offset;
                return;
        }

        if (last_propagated == time_travel_time)
                return;

        time_travel_ext_req(UM_TIMETRAVEL_UPDATE, time_travel_time);
        last_propagated = time_travel_time;
}
EXPORT_SYMBOL_GPL(__time_travel_propagate_time);

/* returns true if we must do a wait to the simtime device */
static bool time_travel_ext_request(unsigned long long time)
{
        /*
         * If we received an external sync point ("free until") then we
         * don't have to request/wait for anything until then, unless
         * we're already waiting.
         *
         * Note for shm we ignore FREE_UNTIL messages and leave the pointer
         * to shared memory, and for non-shm the offset is 0.
         */
        if (!time_travel_ext_waiting && time_travel_ext_free_until &&
            time < (*time_travel_ext_free_until - time_travel_shm_offset))
                return false;

        time_travel_ext_update_request(time);
        return true;
}

static void time_travel_ext_wait(bool idle)
{
        struct um_timetravel_msg msg = {
                .op = UM_TIMETRAVEL_ACK,
        };

        time_travel_ext_prev_request_valid = false;
        if (!time_travel_shm)
                time_travel_ext_free_until = NULL;
        time_travel_ext_waiting++;

        time_travel_ext_req(UM_TIMETRAVEL_WAIT, -1);

        /*
         * Here we are deep in the idle loop, so we have to break out of the
         * kernel abstraction in a sense and implement this in terms of the
         * UML system waiting on the VQ interrupt while sleeping, when we get
         * the signal it'll call time_travel_ext_vq_notify_done() completing the
         * call.
         */
        while (msg.op != UM_TIMETRAVEL_RUN)
                time_travel_handle_message(&msg, idle ? TTMH_IDLE : TTMH_POLL);

        time_travel_ext_waiting--;

        /* we might request more stuff while polling - reset when we run */
        time_travel_ext_prev_request_valid = false;
}

static void time_travel_ext_get_time(void)
{
        if (time_travel_shm)
                time_travel_set_time(time_travel_shm->current_time -
                                     time_travel_shm_offset);
        else
                time_travel_ext_req(UM_TIMETRAVEL_GET, -1);
}

static void __time_travel_update_time(unsigned long long ns, bool idle)
{
        if (time_travel_mode == TT_MODE_EXTERNAL && time_travel_ext_request(ns))
                time_travel_ext_wait(idle);
        else
                time_travel_set_time(ns);
}

static struct time_travel_event *time_travel_first_event(void)
{
        return list_first_entry_or_null(&time_travel_events,
                                        struct time_travel_event,
                                        list);
}

static void __time_travel_add_event(struct time_travel_event *e,
                                    unsigned long long time)
{
        struct time_travel_event *tmp;
        bool inserted = false;
        unsigned long flags;

        if (e->pending)
                return;

        e->pending = true;
        e->time = time;

        local_irq_save(flags);
        list_for_each_entry(tmp, &time_travel_events, list) {
                /*
                 * Add the new entry before one with higher time,
                 * or if they're equal and both on stack, because
                 * in that case we need to unwind the stack in the
                 * right order, and the later event (timer sleep
                 * or such) must be dequeued first.
                 */
                if ((tmp->time > e->time) ||
                    (tmp->time == e->time && tmp->onstack && e->onstack)) {
                        list_add_tail(&e->list, &tmp->list);
                        inserted = true;
                        break;
                }
        }

        if (!inserted)
                list_add_tail(&e->list, &time_travel_events);

        tmp = time_travel_first_event();
        time_travel_ext_update_request(tmp->time);
        time_travel_next_event = tmp->time;
        local_irq_restore(flags);
}

static void time_travel_add_event(struct time_travel_event *e,
                                  unsigned long long time)
{
        if (WARN_ON(!e->fn))
                return;

        __time_travel_add_event(e, time);
}

void time_travel_add_event_rel(struct time_travel_event *e,
                               unsigned long long delay_ns)
{
        time_travel_add_event(e, time_travel_time + delay_ns);
}

static void time_travel_periodic_timer(struct time_travel_event *e)
{
        time_travel_add_event(&time_travel_timer_event,
                              time_travel_time + time_travel_timer_interval);

        /* clock tick; decrease extra jiffies by keeping sched_clock constant */
        if (tt_extra_sched_jiffies > 0)
                tt_extra_sched_jiffies -= 1;

        deliver_alarm();
}

void deliver_time_travel_irqs(void)
{
        struct time_travel_event *e;
        unsigned long flags;

        /*
         * Don't do anything for most cases. Note that because here we have
         * to disable IRQs (and re-enable later) we'll actually recurse at
         * the end of the function, so this is strictly necessary.
         */
        if (likely(list_empty(&time_travel_irqs)))
                return;

        local_irq_save(flags);
        irq_enter();
        while ((e = list_first_entry_or_null(&time_travel_irqs,
                                             struct time_travel_event,
                                             list))) {
                list_del(&e->list);
                e->pending = false;
                e->fn(e);
        }
        irq_exit();
        local_irq_restore(flags);
}

static void time_travel_deliver_event(struct time_travel_event *e)
{
        if (e == &time_travel_timer_event) {
                /*
                 * deliver_alarm() does the irq_enter/irq_exit
                 * by itself, so must handle it specially here
                 */
                e->fn(e);
        } else if (irqs_disabled()) {
                list_add_tail(&e->list, &time_travel_irqs);
                /*
                 * set pending again, it was set to false when the
                 * event was deleted from the original list, but
                 * now it's still pending until we deliver the IRQ.
                 */
                e->pending = true;
        } else {
                unsigned long flags;

                local_irq_save(flags);
                irq_enter();
                e->fn(e);
                irq_exit();
                local_irq_restore(flags);
        }
}

bool time_travel_del_event(struct time_travel_event *e)
{
        unsigned long flags;

        if (!e->pending)
                return false;
        local_irq_save(flags);
        list_del(&e->list);
        e->pending = false;
        local_irq_restore(flags);
        return true;
}

static void time_travel_update_time(unsigned long long next, bool idle)
{
        struct time_travel_event ne = {
                .onstack = true,
        };
        struct time_travel_event *e;
        bool finished = idle;

        /* add it without a handler - we deal with that specifically below */
        __time_travel_add_event(&ne, next);

        do {
                e = time_travel_first_event();

                BUG_ON(!e);
                __time_travel_update_time(e->time, idle);

                /* new events may have been inserted while we were waiting */
                if (e == time_travel_first_event()) {
                        BUG_ON(!time_travel_del_event(e));
                        BUG_ON(time_travel_time != e->time);

                        if (e == &ne) {
                                finished = true;
                        } else {
                                if (e->onstack)
                                        panic("On-stack event dequeued outside of the stack! time=%lld, event time=%lld, event=%pS\n",
                                              time_travel_time, e->time, e);
                                time_travel_deliver_event(e);
                        }
                }

                e = time_travel_first_event();
                if (e)
                        time_travel_ext_update_request(e->time);
        } while (ne.pending && !finished);

        time_travel_del_event(&ne);
}

static void time_travel_update_time_rel(unsigned long long offs)
{
        unsigned long flags;

        /*
         * Disable interrupts before calculating the new time so
         * that a real timer interrupt (signal) can't happen at
         * a bad time e.g. after we read time_travel_time but
         * before we've completed updating the time.
         */
        local_irq_save(flags);
        time_travel_update_time(time_travel_time + offs, false);
        local_irq_restore(flags);
}

void time_travel_ndelay(unsigned long nsec)
{
        /*
         * Not strictly needed to use _rel() version since this is
         * only used in INFCPU/EXT modes, but it doesn't hurt and
         * is more readable too.
         */
        time_travel_update_time_rel(nsec);
}
EXPORT_SYMBOL(time_travel_ndelay);

void time_travel_add_irq_event(struct time_travel_event *e)
{
        BUG_ON(time_travel_mode != TT_MODE_EXTERNAL);

        time_travel_ext_get_time();
        /*
         * We could model interrupt latency here, for now just
         * don't have any latency at all and request the exact
         * same time (again) to run the interrupt...
         */
        time_travel_add_event(e, time_travel_time);
}
EXPORT_SYMBOL_GPL(time_travel_add_irq_event);

static void time_travel_oneshot_timer(struct time_travel_event *e)
{
        /* clock tick; decrease extra jiffies by keeping sched_clock constant */
        if (tt_extra_sched_jiffies > 0)
                tt_extra_sched_jiffies -= 1;

        deliver_alarm();
}

void time_travel_sleep(void)
{
        /*
         * Wait "forever" (using S64_MAX because there are some potential
         * wrapping issues, especially with the current TT_MODE_EXTERNAL
         * controller application.
         */
        unsigned long long next = S64_MAX;
        int cpu = raw_smp_processor_id();

        if (time_travel_mode == TT_MODE_BASIC)
                os_timer_disable(cpu);

        time_travel_update_time(next, true);

        if (time_travel_mode == TT_MODE_BASIC &&
            time_travel_timer_event.pending) {
                if (time_travel_timer_event.fn == time_travel_periodic_timer) {
                        /*
                         * This is somewhat wrong - we should get the first
                         * one sooner like the os_timer_one_shot() below...
                         */
                        os_timer_set_interval(cpu, time_travel_timer_interval);
                } else {
                        os_timer_one_shot(cpu, time_travel_timer_event.time - next);
                }
        }
}

static void time_travel_handle_real_alarm(void)
{
        time_travel_set_time(time_travel_next_event);

        time_travel_del_event(&time_travel_timer_event);

        if (time_travel_timer_event.fn == time_travel_periodic_timer)
                time_travel_add_event(&time_travel_timer_event,
                                      time_travel_time +
                                      time_travel_timer_interval);
}

static void time_travel_set_interval(unsigned long long interval)
{
        time_travel_timer_interval = interval;
}

static int time_travel_connect_external(const char *socket)
{
        const char *sep;
        unsigned long long id = (unsigned long long)-1;
        int rc;

        if ((sep = strchr(socket, ':'))) {
                char buf[25] = {};
                if (sep - socket > sizeof(buf) - 1)
                        goto invalid_number;

                memcpy(buf, socket, sep - socket);
                if (kstrtoull(buf, 0, &id)) {
invalid_number:
                        panic("time-travel: invalid external ID in string '%s'\n",
                              socket);
                        return -EINVAL;
                }

                socket = sep + 1;
        }

        rc = os_connect_socket(socket);
        if (rc < 0) {
                panic("time-travel: failed to connect to external socket %s\n",
                      socket);
                return rc;
        }

        time_travel_ext_fd = rc;

        time_travel_ext_req(UM_TIMETRAVEL_START, id);

        return 1;
}

static void time_travel_set_start(void)
{
        if (time_travel_start_set)
                return;

        switch (time_travel_mode) {
        case TT_MODE_EXTERNAL:
                time_travel_start = time_travel_ext_req(UM_TIMETRAVEL_GET_TOD, -1);
                /* controller gave us the *current* time, so adjust by that */
                time_travel_ext_get_time();
                time_travel_start -= time_travel_time;
                break;
        case TT_MODE_INFCPU:
        case TT_MODE_BASIC:
                if (!time_travel_start_set)
                        time_travel_start = os_persistent_clock_emulation();
                break;
        case TT_MODE_OFF:
                /* we just read the host clock with os_persistent_clock_emulation() */
                break;
        }

        time_travel_start_set = true;
}
#else /* CONFIG_UML_TIME_TRAVEL_SUPPORT */
#define time_travel_start_set 0
#define time_travel_start 0
#define time_travel_time 0
#define time_travel_ext_waiting 0

static inline void time_travel_update_time(unsigned long long ns, bool idle)
{
}

static inline void time_travel_update_time_rel(unsigned long long offs)
{
}

static inline void time_travel_handle_real_alarm(void)
{
}

static void time_travel_set_interval(unsigned long long interval)
{
}

static inline void time_travel_set_start(void)
{
}

/* fail link if this actually gets used */
extern u64 time_travel_ext_req(u32 op, u64 time);

/* these are empty macros so the struct/fn need not exist */
#define time_travel_add_event(e, time) do { } while (0)
/* externally not usable - redefine here so we can */
#undef time_travel_del_event
#define time_travel_del_event(e) do { } while (0)
#endif

static struct clock_event_device timer_clockevent[NR_CPUS];

void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
        unsigned long flags;

        /*
         * In basic time-travel mode we still get real interrupts
         * (signals) but since we don't read time from the OS, we
         * must update the simulated time here to the expiry when
         * we get a signal.
         * This is not the case in inf-cpu mode, since there we
         * never get any real signals from the OS.
         */
        if (time_travel_mode == TT_MODE_BASIC)
                time_travel_handle_real_alarm();

        local_irq_save(flags);
        do_IRQ(TIMER_IRQ, regs);
        local_irq_restore(flags);
}

static int itimer_shutdown(struct clock_event_device *evt)
{
        int cpu = evt - &timer_clockevent[0];

        if (time_travel_mode != TT_MODE_OFF)
                time_travel_del_event(&time_travel_timer_event);

        if (time_travel_mode != TT_MODE_INFCPU &&
            time_travel_mode != TT_MODE_EXTERNAL)
                os_timer_disable(cpu);

        return 0;
}

static int itimer_set_periodic(struct clock_event_device *evt)
{
        unsigned long long interval = NSEC_PER_SEC / HZ;
        int cpu = evt - &timer_clockevent[0];

        if (time_travel_mode != TT_MODE_OFF) {
                time_travel_del_event(&time_travel_timer_event);
                time_travel_set_event_fn(&time_travel_timer_event,
                                         time_travel_periodic_timer);
                time_travel_set_interval(interval);
                time_travel_add_event(&time_travel_timer_event,
                                      time_travel_time + interval);
        }

        if (time_travel_mode != TT_MODE_INFCPU &&
            time_travel_mode != TT_MODE_EXTERNAL)
                os_timer_set_interval(cpu, interval);

        return 0;
}

static int itimer_next_event(unsigned long delta,
                             struct clock_event_device *evt)
{
        delta += 1;

        if (time_travel_mode != TT_MODE_OFF) {
                time_travel_del_event(&time_travel_timer_event);
                time_travel_set_event_fn(&time_travel_timer_event,
                                         time_travel_oneshot_timer);
                time_travel_add_event(&time_travel_timer_event,
                                      time_travel_time + delta);
        }

        if (time_travel_mode != TT_MODE_INFCPU &&
            time_travel_mode != TT_MODE_EXTERNAL)
                return os_timer_one_shot(raw_smp_processor_id(), delta);

        return 0;
}

static int itimer_one_shot(struct clock_event_device *evt)
{
        return itimer_next_event(0, evt);
}

static struct clock_event_device _timer_clockevent = {
        .name                   = "posix-timer",
        .rating                 = 250,
        .features               = CLOCK_EVT_FEAT_PERIODIC |
                                  CLOCK_EVT_FEAT_ONESHOT,
        .set_state_shutdown     = itimer_shutdown,
        .set_state_periodic     = itimer_set_periodic,
        .set_state_oneshot      = itimer_one_shot,
        .set_next_event         = itimer_next_event,
        .shift                  = 0,
        .max_delta_ns           = 0xffffffff,
        .max_delta_ticks        = 0xffffffff,
        .min_delta_ns           = TIMER_MIN_DELTA,
        .min_delta_ticks        = TIMER_MIN_DELTA, // microsecond resolution should be enough for anyone, same as 640K RAM
        .irq                    = 0,
        .mult                   = 1,
};

static irqreturn_t um_timer(int irq, void *dev)
{
        int cpu = raw_smp_processor_id();
        struct clock_event_device *evt = &timer_clockevent[cpu];

        /*
         * Interrupt the (possibly) running userspace process, technically this
         * should only happen if userspace is currently executing.
         * With infinite CPU time-travel, we can only get here when userspace
         * is not executing. Do not notify there and avoid spurious scheduling.
         */
        if (time_travel_mode != TT_MODE_INFCPU &&
            time_travel_mode != TT_MODE_EXTERNAL &&
            get_current()->mm)
                os_alarm_process(get_current()->mm->context.id.pid);

        evt->event_handler(evt);

        return IRQ_HANDLED;
}

static u64 timer_read(struct clocksource *cs)
{
        if (time_travel_mode != TT_MODE_OFF) {
                /*
                 * We make reading the timer cost a bit so that we don't get
                 * stuck in loops that expect time to move more than the
                 * exact requested sleep amount, e.g. python's socket server,
                 * see https://bugs.python.org/issue37026.
                 *
                 * However, don't do that when we're in interrupt or such as
                 * then we might recurse into our own processing, and get to
                 * even more waiting, and that's not good - it messes up the
                 * "what do I do next" and onstack event we use to know when
                 * to return from time_travel_update_time().
                 */
                if (!irqs_disabled() && !in_interrupt() && !in_softirq() &&
                    !time_travel_ext_waiting)
                        time_travel_update_time_rel(TIMER_MULTIPLIER);
                return time_travel_time / TIMER_MULTIPLIER;
        }

        return os_nsecs() / TIMER_MULTIPLIER;
}

static struct clocksource timer_clocksource = {
        .name           = "timer",
        .rating         = 300,
        .read           = timer_read,
        .mask           = CLOCKSOURCE_MASK(64),
        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
};

int um_setup_timer(void)
{
        int cpu = raw_smp_processor_id();
        struct clock_event_device *evt = &timer_clockevent[cpu];
        int err;

        err = os_timer_create();
        if (err)
                return err;

        memcpy(evt, &_timer_clockevent, sizeof(*evt));
        evt->cpumask = cpumask_of(cpu);
        clockevents_register_device(evt);

        return 0;
}

static void __init um_timer_init(void)
{
        int err;

        err = request_irq(TIMER_IRQ, um_timer, IRQF_TIMER, "hr timer", NULL);
        if (err != 0)
                printk(KERN_ERR "register_timer : request_irq failed - "
                       "errno = %d\n", -err);

        err = um_setup_timer();
        if (err) {
                printk(KERN_ERR "creation of timer failed - errno = %d\n", -err);
                return;
        }

        err = clocksource_register_hz(&timer_clocksource, NSEC_PER_SEC/TIMER_MULTIPLIER);
        if (err) {
                printk(KERN_ERR "clocksource_register_hz returned %d\n", err);
                return;
        }
}

void read_persistent_clock64(struct timespec64 *ts)
{
        long long nsecs;

        time_travel_set_start();

        if (time_travel_mode != TT_MODE_OFF)
                nsecs = time_travel_start + time_travel_time;
        else
                nsecs = os_persistent_clock_emulation();

        set_normalized_timespec64(ts, nsecs / NSEC_PER_SEC,
                                  nsecs % NSEC_PER_SEC);
}

void __init time_init(void)
{
        timer_set_signal_handler();
        late_time_init = um_timer_init;
}

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
unsigned long calibrate_delay_is_known(void)
{
        if (time_travel_mode == TT_MODE_INFCPU ||
            time_travel_mode == TT_MODE_EXTERNAL)
                return 1;
        return 0;
}

static int setup_time_travel(char *str)
{
        if (strcmp(str, "=inf-cpu") == 0) {
                time_travel_mode = TT_MODE_INFCPU;
                _timer_clockevent.name = "time-travel-timer-infcpu";
                timer_clocksource.name = "time-travel-clock";
                return 1;
        }

        if (strncmp(str, "=ext:", 5) == 0) {
                time_travel_mode = TT_MODE_EXTERNAL;
                _timer_clockevent.name = "time-travel-timer-external";
                timer_clocksource.name = "time-travel-clock-external";
                return time_travel_connect_external(str + 5);
        }

        if (!*str) {
                time_travel_mode = TT_MODE_BASIC;
                _timer_clockevent.name = "time-travel-timer";
                timer_clocksource.name = "time-travel-clock";
                return 1;
        }

        return -EINVAL;
}

__setup("time-travel", setup_time_travel);
__uml_help(setup_time_travel,
"time-travel\n"
"    This option just enables basic time travel mode, in which the clock/timers\n"
"    inside the UML instance skip forward when there's nothing to do, rather than\n"
"    waiting for real time to elapse. However, instance CPU speed is limited by\n"
"    the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
"    clock (but quicker when there's nothing to do).\n"
"\n"
"time-travel=inf-cpu\n"
"    This enables time travel mode with infinite processing power, in which there\n"
"    are no wall clock timers, and any CPU processing happens - as seen from the\n"
"    guest - instantly. This can be useful for accurate simulation regardless of\n"
"    debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
"    easily lead to getting stuck (e.g. if anything in the system busy loops).\n"
"\n"
"time-travel=ext:[ID:]/path/to/socket\n"
"    This enables time travel mode similar to =inf-cpu, except the system will\n"
"    use the given socket to coordinate with a central scheduler, in order to\n"
"    have more than one system simultaneously be on simulated time. The virtio\n"
"    driver code in UML knows about this so you can also simulate networks and\n"
"    devices using it, assuming the device has the right capabilities.\n"
"    The optional ID is a 64-bit integer that's sent to the central scheduler.\n\n");

static int setup_time_travel_start(char *str)
{
        int err;

        err = kstrtoull(str, 0, &time_travel_start);
        if (err)
                return err;

        time_travel_start_set = 1;
        return 1;
}

__setup("time-travel-start=", setup_time_travel_start);
__uml_help(setup_time_travel_start,
"time-travel-start=<nanoseconds>\n"
"    Configure the UML instance's wall clock to start at this value rather than\n"
"    the host's wall clock at the time of UML boot.\n\n");

static struct kobject *bc_time_kobject;

static ssize_t bc_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
{
        return sprintf(buf, "0x%llx", bc_message);
}

static ssize_t bc_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count)
{
        int ret;
        u64 user_bc_message;

        ret = kstrtou64(buf, 0, &user_bc_message);
        if (ret)
                return ret;

        bc_message = user_bc_message;

        time_travel_ext_req(UM_TIMETRAVEL_BROADCAST, bc_message);
        pr_info("um: time: sent broadcast message: 0x%llx\n", bc_message);
        return count;
}

static struct kobj_attribute bc_attribute = __ATTR(bc-message, 0660, bc_show, bc_store);

static int __init um_bc_start(void)
{
        if (time_travel_mode != TT_MODE_EXTERNAL)
                return 0;

        bc_time_kobject = kobject_create_and_add("um-ext-time", kernel_kobj);
        if (!bc_time_kobject)
                return 0;

        if (sysfs_create_file(bc_time_kobject, &bc_attribute.attr))
                pr_debug("failed to create the bc file in /sys/kernel/um_time");

        return 0;
}
late_initcall(um_bc_start);
#endif