evtchn.c

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/******************************************************************************
 * 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.
 */

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

struct per_user_data {
    struct mutex bind_mutex; /* serialize bind/unbind operations */

    /* Notification ring, accessed via /dev/xen/evtchn. */
#define EVTCHN_RING_SIZE     (PAGE_SIZE / sizeof(evtchn_port_t))
#define EVTCHN_RING_MASK(_i) ((_i)&(EVTCHN_RING_SIZE-1))
    evtchn_port_t *ring;
    unsigned int ring_cons, ring_prod, ring_overflow;
    struct mutex ring_cons_mutex; /* protect against concurrent readers */

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

/*
 * Who's bound to each port?  This is logically an array of struct
 * per_user_data *, but we encode the current enabled-state in bit 0.
 */
static unsigned long *port_user;
static DEFINE_SPINLOCK(port_user_lock); /* protects port_user[] and ring_prod */

static inline struct per_user_data *get_port_user(unsigned port)
{
    return (struct per_user_data *)(port_user[port] & ~1);
}

static inline void set_port_user(unsigned port, struct per_user_data *u)
{
    port_user[port] = (unsigned long)u;
}

static inline bool get_port_enabled(unsigned port)
{
    return port_user[port] & 1;
}

static inline void set_port_enabled(unsigned port, bool enabled)
{
    if (enabled)
        port_user[port] |= 1;
    else
        port_user[port] &= ~1;
}

static irqreturn_t evtchn_interrupt(int irq, void *data)
{
    unsigned int port = (unsigned long)data;
    struct per_user_data *u;

    spin_lock(&port_user_lock);

    u = get_port_user(port);

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

    disable_irq_nosync(irq);
    set_port_enabled(port, false);

    if ((u->ring_prod - u->ring_cons) < EVTCHN_RING_SIZE) {
        u->ring[EVTCHN_RING_MASK(u->ring_prod)] = port;
        wmb(); /* Ensure ring contents visible */
        if (u->ring_cons == u->ring_prod++) {
            wake_up_interruptible(&u->evtchn_wait);
            kill_fasync(&u->evtchn_async_queue,
                    SIGIO, POLL_IN);
        }
    } else
        u->ring_overflow = 1;

    spin_unlock(&port_user_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 = u->ring_cons;
        p = 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,
                          u->ring_cons != u->ring_prod);
        if (rc)
            return rc;
    }

    /* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
    if (((c ^ p) & EVTCHN_RING_SIZE) != 0) {
        bytes1 = (EVTCHN_RING_SIZE - EVTCHN_RING_MASK(c)) *
            sizeof(evtchn_port_t);
        bytes2 = EVTCHN_RING_MASK(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;
    rmb(); /* Ensure that we see the port before we copy it. */
    if (copy_to_user(buf, &u->ring[EVTCHN_RING_MASK(c)], bytes1) ||
        ((bytes2 != 0) &&
         copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
        goto unlock_out;

    u->ring_cons += (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;

    spin_lock_irq(&port_user_lock);

    for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
        unsigned port = kbuf[i];

        if (port < NR_EVENT_CHANNELS &&
            get_port_user(port) == u &&
            !get_port_enabled(port)) {
            set_port_enabled(port, true);
            enable_irq(irq_from_evtchn(port));
        }
    }

    spin_unlock_irq(&port_user_lock);

    rc = count;

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

static int evtchn_bind_to_user(struct per_user_data *u, int port)
{
    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.)
     */
    BUG_ON(get_port_user(port) != NULL);
    set_port_user(port, u);
    set_port_enabled(port, true); /* start enabled */

    rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, IRQF_DISABLED,
                       u->name, (void *)(unsigned long)port);
    if (rc >= 0)
        rc = evtchn_make_refcounted(port);

    return rc;
}

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

    unbind_from_irqhandler(irq, (void *)(unsigned long)port);

    set_port_user(port, NULL);
}

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

        bind_virq.virq = bind.virq;
        bind_virq.vcpu = 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;

        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 = -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;

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

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

        spin_lock_irq(&port_user_lock);

        rc = -ENOTCONN;
        if (get_port_user(unbind.port) != u) {
            spin_unlock_irq(&port_user_lock);
            break;
        }

        disable_irq(irq_from_evtchn(unbind.port));

        spin_unlock_irq(&port_user_lock);

        evtchn_unbind_from_user(u, unbind.port);

        rc = 0;
        break;
    }

    case IOCTL_EVTCHN_NOTIFY: {
        struct ioctl_evtchn_notify notify;

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

        if (notify.port >= NR_EVENT_CHANNELS) {
            rc = -EINVAL;
        } else if (get_port_user(notify.port) != u) {
            rc = -ENOTCONN;
        } else {
            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(&port_user_lock);
        u->ring_cons = u->ring_prod = u->ring_overflow = 0;
        spin_unlock_irq(&port_user_lock);
        mutex_unlock(&u->ring_cons_mutex);
        rc = 0;
        break;
    }

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

    return rc;
}

static unsigned int evtchn_poll(struct file *file, poll_table *wait)
{
    unsigned int mask = POLLOUT | POLLWRNORM;
    struct per_user_data *u = file->private_data;

    poll_wait(file, &u->evtchn_wait, wait);
    if (u->ring_cons != u->ring_prod)
        mask |= POLLIN | POLLRDNORM;
    if (u->ring_overflow)
        mask = POLLERR;
    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);

    u->ring = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
    if (u->ring == NULL) {
        kfree(u->name);
        kfree(u);
        return -ENOMEM;
    }

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

    filp->private_data = u;

    return nonseekable_open(inode, filp);
}

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

    spin_lock_irq(&port_user_lock);

    free_page((unsigned long)u->ring);

    for (i = 0; i < NR_EVENT_CHANNELS; i++) {
        if (get_port_user(i) != u)
            continue;

        disable_irq(irq_from_evtchn(i));
    }

    spin_unlock_irq(&port_user_lock);

    for (i = 0; i < NR_EVENT_CHANNELS; i++) {
        if (get_port_user(i) != u)
            continue;

        evtchn_unbind_from_user(get_port_user(i), i);
    }

    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;

    port_user = kcalloc(NR_EVENT_CHANNELS, sizeof(*port_user), GFP_KERNEL);
    if (port_user == NULL)
        return -ENOMEM;

    spin_lock_init(&port_user_lock);

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

    printk(KERN_INFO "Event-channel device installed.\n");

    return 0;
}

static void __exit evtchn_cleanup(void)
{
    kfree(port_user);
    port_user = NULL;

    misc_deregister(&evtchn_miscdev);
}

module_init(evtchn_init);
module_exit(evtchn_cleanup);

MODULE_LICENSE("GPL");