time.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
 * Copyright (C) 2015 Thomas Meyer ([email protected])
 * 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