evtchn.c

/******************************************************************************
 * evtchn.c
 *
 * Driver for receiving and demuxing event-channel signals.
 *
 * Copyright (c) 2004-2005, K A Fraser
 * Multi-process extensions Copyright (c) 2004, Steven Smith
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/major.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/poll.h>
#include <linux/irq.h>
#include <linux/init.h>
#include <linux/mutex.h>
#include <linux/cpu.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>

#include <xen/xen.h>
#include <xen/events.h>
#include <xen/evtchn.h>
#include <xen/xen-ops.h>
#include <asm/xen/hypervisor.h>

struct per_user_data {
	struct mutex bind_mutex; /* serialize bind/unbind operations */
	struct rb_root evtchns;
	unsigned int nr_evtchns;

	/* Notification ring, accessed via /dev/xen/evtchn. */
	unsigned int ring_size;
	evtchn_port_t *ring;
	unsigned int ring_cons, ring_prod, ring_overflow;
	struct mutex ring_cons_mutex; /* protect against concurrent readers */
	spinlock_t ring_prod_lock; /* product against concurrent interrupts */

	/* Processes wait on this queue when ring is empty. */
	wait_queue_head_t evtchn_wait;
	struct fasync_struct *evtchn_async_queue;
	const char *name;

	domid_t restrict_domid;
};

#define UNRESTRICTED_DOMID ((domid_t)-1)

struct user_evtchn {
	struct rb_node node;
	struct per_user_data *user;
	evtchn_port_t port;
	bool enabled;
};

static void evtchn_free_ring(evtchn_port_t *ring)
{
	kvfree(ring);
}

static unsigned int evtchn_ring_offset(struct per_user_data *u,
				       unsigned int idx)
{
	return idx & (u->ring_size - 1);
}

static evtchn_port_t *evtchn_ring_entry(struct per_user_data *u,
					unsigned int idx)
{
	return u->ring + evtchn_ring_offset(u, idx);
}

static int add_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
{
	struct rb_node **new = &(u->evtchns.rb_node), *parent = NULL;

	u->nr_evtchns++;

	while (*new) {
		struct user_evtchn *this;

		this = rb_entry(*new, struct user_evtchn, node);

		parent = *new;
		if (this->port < evtchn->port)
			new = &((*new)->rb_left);
		else if (this->port > evtchn->port)
			new = &((*new)->rb_right);
		else
			return -EEXIST;
	}

	/* Add new node and rebalance tree. */
	rb_link_node(&evtchn->node, parent, new);
	rb_insert_color(&evtchn->node, &u->evtchns);

	return 0;
}

static void del_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
{
	u->nr_evtchns--;
	rb_erase(&evtchn->node, &u->evtchns);
	kfree(evtchn);
}

static struct user_evtchn *find_evtchn(struct per_user_data *u,
				       evtchn_port_t port)
{
	struct rb_node *node = u->evtchns.rb_node;

	while (node) {
		struct user_evtchn *evtchn;

		evtchn = rb_entry(node, struct user_evtchn, node);

		if (evtchn->port < port)
			node = node->rb_left;
		else if (evtchn->port > port)
			node = node->rb_right;
		else
			return evtchn;
	}
	return NULL;
}

static irqreturn_t evtchn_interrupt(int irq, void *data)
{
	struct user_evtchn *evtchn = data;
	struct per_user_data *u = evtchn->user;
	unsigned int prod, cons;

	WARN(!evtchn->enabled,
	     "Interrupt for port %u, but apparently not enabled; per-user %p\n",
	     evtchn->port, u);

	evtchn->enabled = false;

	spin_lock(&u->ring_prod_lock);

	prod = READ_ONCE(u->ring_prod);
	cons = READ_ONCE(u->ring_cons);

	if ((prod - cons) < u->ring_size) {
		*evtchn_ring_entry(u, prod) = evtchn->port;
		smp_wmb(); /* Ensure ring contents visible */
		WRITE_ONCE(u->ring_prod, prod + 1);
		if (cons == prod) {
			wake_up_interruptible(&u->evtchn_wait);
			kill_fasync(&u->evtchn_async_queue,
				    SIGIO, POLL_IN);
		}
	} else
		u->ring_overflow = 1;

	spin_unlock(&u->ring_prod_lock);

	return IRQ_HANDLED;
}

static ssize_t evtchn_read(struct file *file, char __user *buf,
			   size_t count, loff_t *ppos)
{
	int rc;
	unsigned int c, p, bytes1 = 0, bytes2 = 0;
	struct per_user_data *u = file->private_data;

	/* Whole number of ports. */
	count &= ~(sizeof(evtchn_port_t)-1);

	if (count == 0)
		return 0;

	if (count > PAGE_SIZE)
		count = PAGE_SIZE;

	for (;;) {
		mutex_lock(&u->ring_cons_mutex);

		rc = -EFBIG;
		if (u->ring_overflow)
			goto unlock_out;

		c = READ_ONCE(u->ring_cons);
		p = READ_ONCE(u->ring_prod);
		if (c != p)
			break;

		mutex_unlock(&u->ring_cons_mutex);

		if (file->f_flags & O_NONBLOCK)
			return -EAGAIN;

		rc = wait_event_interruptible(u->evtchn_wait,
			READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod));
		if (rc)
			return rc;
	}

	/* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
	if (((c ^ p) & u->ring_size) != 0) {
		bytes1 = (u->ring_size - evtchn_ring_offset(u, c)) *
			sizeof(evtchn_port_t);
		bytes2 = evtchn_ring_offset(u, p) * sizeof(evtchn_port_t);
	} else {
		bytes1 = (p - c) * sizeof(evtchn_port_t);
		bytes2 = 0;
	}

	/* Truncate chunks according to caller's maximum byte count. */
	if (bytes1 > count) {
		bytes1 = count;
		bytes2 = 0;
	} else if ((bytes1 + bytes2) > count) {
		bytes2 = count - bytes1;
	}

	rc = -EFAULT;
	smp_rmb(); /* Ensure that we see the port before we copy it. */
	if (copy_to_user(buf, evtchn_ring_entry(u, c), bytes1) ||
	    ((bytes2 != 0) &&
	     copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
		goto unlock_out;

	WRITE_ONCE(u->ring_cons, c + (bytes1 + bytes2) / sizeof(evtchn_port_t));
	rc = bytes1 + bytes2;

 unlock_out:
	mutex_unlock(&u->ring_cons_mutex);
	return rc;
}

static ssize_t evtchn_write(struct file *file, const char __user *buf,
			    size_t count, loff_t *ppos)
{
	int rc, i;
	evtchn_port_t *kbuf = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
	struct per_user_data *u = file->private_data;

	if (kbuf == NULL)
		return -ENOMEM;

	/* Whole number of ports. */
	count &= ~(sizeof(evtchn_port_t)-1);

	rc = 0;
	if (count == 0)
		goto out;

	if (count > PAGE_SIZE)
		count = PAGE_SIZE;

	rc = -EFAULT;
	if (copy_from_user(kbuf, buf, count) != 0)
		goto out;

	mutex_lock(&u->bind_mutex);

	for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
		evtchn_port_t port = kbuf[i];
		struct user_evtchn *evtchn;

		evtchn = find_evtchn(u, port);
		if (evtchn && !evtchn->enabled) {
			evtchn->enabled = true;
			xen_irq_lateeoi(irq_from_evtchn(port), 0);
		}
	}

	mutex_unlock(&u->bind_mutex);

	rc = count;

 out:
	free_page((unsigned long)kbuf);
	return rc;
}

static int evtchn_resize_ring(struct per_user_data *u)
{
	unsigned int new_size;
	evtchn_port_t *new_ring, *old_ring;

	/*
	 * Ensure the ring is large enough to capture all possible
	 * events. i.e., one free slot for each bound event.
	 */
	if (u->nr_evtchns <= u->ring_size)
		return 0;

	if (u->ring_size == 0)
		new_size = 64;
	else
		new_size = 2 * u->ring_size;

	new_ring = kvmalloc_array(new_size, sizeof(*new_ring), GFP_KERNEL);
	if (!new_ring)
		return -ENOMEM;

	old_ring = u->ring;

	/*
	 * Access to the ring contents is serialized by either the
	 * prod /or/ cons lock so take both when resizing.
	 */
	mutex_lock(&u->ring_cons_mutex);
	spin_lock_irq(&u->ring_prod_lock);

	/*
	 * Copy the old ring contents to the new ring.
	 *
	 * To take care of wrapping, a full ring, and the new index
	 * pointing into the second half, simply copy the old contents
	 * twice.
	 *
	 * +---------+    +------------------+
	 * |34567  12| -> |34567  1234567  12|
	 * +-----p-c-+    +-------c------p---+
	 */
	memcpy(new_ring, old_ring, u->ring_size * sizeof(*u->ring));
	memcpy(new_ring + u->ring_size, old_ring,
	       u->ring_size * sizeof(*u->ring));

	u->ring = new_ring;
	u->ring_size = new_size;

	spin_unlock_irq(&u->ring_prod_lock);
	mutex_unlock(&u->ring_cons_mutex);

	evtchn_free_ring(old_ring);

	return 0;
}

static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port)
{
	struct user_evtchn *evtchn;
	struct evtchn_close close;
	int rc = 0;

	/*
	 * Ports are never reused, so every caller should pass in a
	 * unique port.
	 *
	 * (Locking not necessary because we haven't registered the
	 * interrupt handler yet, and our caller has already
	 * serialized bind operations.)
	 */

	evtchn = kzalloc(sizeof(*evtchn), GFP_KERNEL);
	if (!evtchn)
		return -ENOMEM;

	evtchn->user = u;
	evtchn->port = port;
	evtchn->enabled = true; /* start enabled */

	rc = add_evtchn(u, evtchn);
	if (rc < 0)
		goto err;

	rc = evtchn_resize_ring(u);
	if (rc < 0)
		goto err;

	rc = bind_evtchn_to_irqhandler_lateeoi(port, evtchn_interrupt, 0,
					       u->name, evtchn);
	if (rc < 0)
		goto err;

	rc = evtchn_make_refcounted(port);
	return rc;

err:
	/* bind failed, should close the port now */
	close.port = port;
	if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
		BUG();
	del_evtchn(u, evtchn);
	return rc;
}

static void evtchn_unbind_from_user(struct per_user_data *u,
				    struct user_evtchn *evtchn)
{
	int irq = irq_from_evtchn(evtchn->port);

	BUG_ON(irq < 0);

	unbind_from_irqhandler(irq, evtchn);

	del_evtchn(u, evtchn);
}

static long evtchn_ioctl(struct file *file,
			 unsigned int cmd, unsigned long arg)
{
	int rc;
	struct per_user_data *u = file->private_data;
	void __user *uarg = (void __user *) arg;

	/* Prevent bind from racing with unbind */
	mutex_lock(&u->bind_mutex);

	switch (cmd) {
	case IOCTL_EVTCHN_BIND_VIRQ: {
		struct ioctl_evtchn_bind_virq bind;
		struct evtchn_bind_virq bind_virq;

		rc = -EACCES;
		if (u->restrict_domid != UNRESTRICTED_DOMID)
			break;

		rc = -EFAULT;
		if (copy_from_user(&bind, uarg, sizeof(bind)))
			break;

		bind_virq.virq = bind.virq;
		bind_virq.vcpu = xen_vcpu_nr(0);
		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
						 &bind_virq);
		if (rc != 0)
			break;

		rc = evtchn_bind_to_user(u, bind_virq.port);
		if (rc == 0)
			rc = bind_virq.port;
		break;
	}

	case IOCTL_EVTCHN_BIND_INTERDOMAIN: {
		struct ioctl_evtchn_bind_interdomain bind;
		struct evtchn_bind_interdomain bind_interdomain;

		rc = -EFAULT;
		if (copy_from_user(&bind, uarg, sizeof(bind)))
			break;

		rc = -EACCES;
		if (u->restrict_domid != UNRESTRICTED_DOMID &&
		    u->restrict_domid != bind.remote_domain)
			break;

		bind_interdomain.remote_dom  = bind.remote_domain;
		bind_interdomain.remote_port = bind.remote_port;
		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
						 &bind_interdomain);
		if (rc != 0)
			break;

		rc = evtchn_bind_to_user(u, bind_interdomain.local_port);
		if (rc == 0)
			rc = bind_interdomain.local_port;
		break;
	}

	case IOCTL_EVTCHN_BIND_UNBOUND_PORT: {
		struct ioctl_evtchn_bind_unbound_port bind;
		struct evtchn_alloc_unbound alloc_unbound;

		rc = -EACCES;
		if (u->restrict_domid != UNRESTRICTED_DOMID)
			break;

		rc = -EFAULT;
		if (copy_from_user(&bind, uarg, sizeof(bind)))
			break;

		alloc_unbound.dom        = DOMID_SELF;
		alloc_unbound.remote_dom = bind.remote_domain;
		rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
						 &alloc_unbound);
		if (rc != 0)
			break;

		rc = evtchn_bind_to_user(u, alloc_unbound.port);
		if (rc == 0)
			rc = alloc_unbound.port;
		break;
	}

	case IOCTL_EVTCHN_UNBIND: {
		struct ioctl_evtchn_unbind unbind;
		struct user_evtchn *evtchn;

		rc = -EFAULT;
		if (copy_from_user(&unbind, uarg, sizeof(unbind)))
			break;

		rc = -EINVAL;
		if (unbind.port >= xen_evtchn_nr_channels())
			break;

		rc = -ENOTCONN;
		evtchn = find_evtchn(u, unbind.port);
		if (!evtchn)
			break;

		disable_irq(irq_from_evtchn(unbind.port));
		evtchn_unbind_from_user(u, evtchn);
		rc = 0;
		break;
	}

	case IOCTL_EVTCHN_NOTIFY: {
		struct ioctl_evtchn_notify notify;
		struct user_evtchn *evtchn;

		rc = -EFAULT;
		if (copy_from_user(&notify, uarg, sizeof(notify)))
			break;

		rc = -ENOTCONN;
		evtchn = find_evtchn(u, notify.port);
		if (evtchn) {
			notify_remote_via_evtchn(notify.port);
			rc = 0;
		}
		break;
	}

	case IOCTL_EVTCHN_RESET: {
		/* Initialise the ring to empty. Clear errors. */
		mutex_lock(&u->ring_cons_mutex);
		spin_lock_irq(&u->ring_prod_lock);
		WRITE_ONCE(u->ring_cons, 0);
		WRITE_ONCE(u->ring_prod, 0);
		u->ring_overflow = 0;
		spin_unlock_irq(&u->ring_prod_lock);
		mutex_unlock(&u->ring_cons_mutex);
		rc = 0;
		break;
	}

	case IOCTL_EVTCHN_RESTRICT_DOMID: {
		struct ioctl_evtchn_restrict_domid ierd;

		rc = -EACCES;
		if (u->restrict_domid != UNRESTRICTED_DOMID)
			break;

		rc = -EFAULT;
		if (copy_from_user(&ierd, uarg, sizeof(ierd)))
		    break;

		rc = -EINVAL;
		if (ierd.domid == 0 || ierd.domid >= DOMID_FIRST_RESERVED)
			break;

		u->restrict_domid = ierd.domid;
		rc = 0;

		break;
	}

	default:
		rc = -ENOSYS;
		break;
	}
	mutex_unlock(&u->bind_mutex);

	return rc;
}

static __poll_t evtchn_poll(struct file *file, poll_table *wait)
{
	__poll_t mask = EPOLLOUT | EPOLLWRNORM;
	struct per_user_data *u = file->private_data;

	poll_wait(file, &u->evtchn_wait, wait);
	if (READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod))
		mask |= EPOLLIN | EPOLLRDNORM;
	if (u->ring_overflow)
		mask = EPOLLERR;
	return mask;
}

static int evtchn_fasync(int fd, struct file *filp, int on)
{
	struct per_user_data *u = filp->private_data;
	return fasync_helper(fd, filp, on, &u->evtchn_async_queue);
}

static int evtchn_open(struct inode *inode, struct file *filp)
{
	struct per_user_data *u;

	u = kzalloc(sizeof(*u), GFP_KERNEL);
	if (u == NULL)
		return -ENOMEM;

	u->name = kasprintf(GFP_KERNEL, "evtchn:%s", current->comm);
	if (u->name == NULL) {
		kfree(u);
		return -ENOMEM;
	}

	init_waitqueue_head(&u->evtchn_wait);

	mutex_init(&u->bind_mutex);
	mutex_init(&u->ring_cons_mutex);
	spin_lock_init(&u->ring_prod_lock);

	u->restrict_domid = UNRESTRICTED_DOMID;

	filp->private_data = u;

	return stream_open(inode, filp);
}

static int evtchn_release(struct inode *inode, struct file *filp)
{
	struct per_user_data *u = filp->private_data;
	struct rb_node *node;

	while ((node = u->evtchns.rb_node)) {
		struct user_evtchn *evtchn;

		evtchn = rb_entry(node, struct user_evtchn, node);
		disable_irq(irq_from_evtchn(evtchn->port));
		evtchn_unbind_from_user(u, evtchn);
	}

	evtchn_free_ring(u->ring);
	kfree(u->name);
	kfree(u);

	return 0;
}

static const struct file_operations evtchn_fops = {
	.owner   = THIS_MODULE,
	.read    = evtchn_read,
	.write   = evtchn_write,
	.unlocked_ioctl = evtchn_ioctl,
	.poll    = evtchn_poll,
	.fasync  = evtchn_fasync,
	.open    = evtchn_open,
	.release = evtchn_release,
	.llseek	 = no_llseek,
};

static struct miscdevice evtchn_miscdev = {
	.minor        = MISC_DYNAMIC_MINOR,
	.name         = "xen/evtchn",
	.fops         = &evtchn_fops,
};
static int __init evtchn_init(void)
{
	int err;

	if (!xen_domain())
		return -ENODEV;

	/* Create '/dev/xen/evtchn'. */
	err = misc_register(&evtchn_miscdev);
	if (err != 0) {
		pr_err("Could not register /dev/xen/evtchn\n");
		return err;
	}

	pr_info("Event-channel device installed\n");

	return 0;
}

static void __exit evtchn_cleanup(void)
{
	misc_deregister(&evtchn_miscdev);
}

module_init(evtchn_init);
module_exit(evtchn_cleanup);

MODULE_LICENSE("GPL");