/******************************************************************************
 * 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");