path: root/arch/um/kernel/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 (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/time-internal.h>
#include <linux/um_timetravel.h>
#include <shared/init.h>

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
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 LIST_HEAD(time_travel_events);
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 bool time_travel_ext_free_until_valid;
static unsigned long long time_travel_ext_free_until;

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,
};

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;

	/*
	 * Poll outside the locked section (if we're not called to only read
	 * the response) so we can get interrupts for e.g. virtio while we're
	 * here, but then we need to lock to not get interrupted between the
	 * read of the message and write of the ACK.
	 */
	if (mode != TTMH_READ) {
		bool disabled = irqs_disabled();

		BUG_ON(mode == TTMH_IDLE && !disabled);

		if (disabled)
			local_irq_enable();
		while (os_poll(1, &time_travel_ext_fd) != 0) {
			/* nothing */
		}
		if (disabled)
			local_irq_disable();
	}

	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);
		break;
	case UM_TIMETRAVEL_FREE_UNTIL:
		time_travel_ext_free_until_valid = true;
		time_travel_ext_free_until = msg->time;
		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,
	};
	unsigned long flags;

	/*
	 * We need to save interrupts here and only restore when we
	 * got the ACK - otherwise we can get interrupted and 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.
	 */
	local_irq_save(flags);
	os_write_file(time_travel_ext_fd, &msg, sizeof(msg));

	while (msg.op != UM_TIMETRAVEL_ACK)
		time_travel_handle_message(&msg, 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);
	local_irq_restore(flags);

	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;

	time_travel_ext_prev_request = time;
	time_travel_ext_prev_request_valid = true;
	time_travel_ext_req(UM_TIMETRAVEL_REQUEST, time);
}

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

	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.
	 */
	if (!time_travel_ext_waiting && time_travel_ext_free_until_valid &&
	    time < time_travel_ext_free_until)
		return false;

	time_travel_ext_update_request(time);