/******************************************************************************
 * gntalloc.c
 *
 * Device for creating grant references (in user-space) that may be shared
 * with other domains.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/*
 * This driver exists to allow userspace programs in Linux to allocate kernel
 * memory that will later be shared with another domain.  Without this device,
 * Linux userspace programs cannot create grant references.
 *
 * How this stuff works:
 *   X -> granting a page to Y
 *   Y -> mapping the grant from X
 *
 *   1. X uses the gntalloc device to allocate a page of kernel memory, P.
 *   2. X creates an entry in the grant table that says domid(Y) can access P.
 *      This is done without a hypercall unless the grant table needs expansion.
 *   3. X gives the grant reference identifier, GREF, to Y.
 *   4. Y maps the page, either directly into kernel memory for use in a backend
 *      driver, or via a the gntdev device to map into the address space of an
 *      application running in Y. This is the first point at which Xen does any
 *      tracking of the page.
 *   5. A program in X mmap()s a segment of the gntalloc device that corresponds
 *      to the shared page, and can now communicate with Y over the shared page.
 *
 *
 * NOTE TO USERSPACE LIBRARIES:
 *   The grant allocation and mmap()ing are, naturally, two separate operations.
 *   You set up the sharing by calling the create ioctl() and then the mmap().
 *   Teardown requires munmap() and either close() or ioctl().
 *
 * WARNING: Since Xen does not allow a guest to forcibly end the use of a grant
 * reference, this device can be used to consume kernel memory by leaving grant
 * references mapped by another domain when an application exits. Therefore,
 * there is a global limit on the number of pages that can be allocated. When
 * all references to the page are unmapped, it will be freed during the next
 * grant operation.
 */

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

#include <linux/atomic.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/highmem.h>

#include <xen/xen.h>
#include <xen/page.h>
#include <xen/grant_table.h>
#include <xen/gntalloc.h>
#include <xen/events.h>

static int limit = 1024;
module_param(limit, int, 0644);
MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
                "the gntalloc device");

static LIST_HEAD(gref_list);
static DEFINE_MUTEX(gref_mutex);
static int gref_size;

struct notify_info {
        uint16_t pgoff:12;    /* Bits 0-11: Offset of the byte to clear */
        uint16_t flags:2;     /* Bits 12-13: Unmap notification flags */
        int event;            /* Port (event channel) to notify */
};

/* Metadata on a grant reference. */
struct gntalloc_gref {
        struct list_head next_gref;  /* list entry gref_list */
        struct list_head next_file;  /* list entry file->list, if open */
        struct page *page;           /* The shared page */
        uint64_t file_index;         /* File offset for mmap() */
        unsigned int users;          /* Use count - when zero, waiting on Xen */
        grant_ref_t gref_id;         /* The grant reference number */
        struct notify_info notify;   /* Unmap notification */
};

struct gntalloc_file_private_data {
        struct list_head list;
        uint64_t index;
};

struct gntalloc_vma_private_data {
        struct gntalloc_gref *gref;
        int users;
        int count;
};

static void __del_gref(struct gntalloc_gref *gref);

static void do_cleanup(void)
{
        struct gntalloc_gref *gref, *n;
        list_for_each_entry_safe(gref, n, &gref_list, next_gref) {
                if (!gref->users)
                        __del_gref(gref);
        }
}

static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
        uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
{
        int i, rc, readonly;
        LIST_HEAD(queue_gref);
        LIST_HEAD(queue_file);
        struct gntalloc_gref *gref, *next;

        readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
        for (i = 0; i < op->count; i++) {
                gref = kzalloc(sizeof(*gref), GFP_KERNEL);
                if (!gref) {
                        rc = -ENOMEM;
                        goto undo;
                }
                list_add_tail(&gref->next_gref, &queue_gref);
                list_add_tail(&gref->next_file, &queue_file);
                gref->users = 1;
                gref->file_index = op->index + i * PAGE_SIZE;
                gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
                if (!gref->page) {
                        rc = -ENOMEM;
                        goto undo;
                }

                /* Grant foreign access to the page. */
                rc = gnttab_grant_foreign_access(op->domid,
                                                 xen_page_to_gfn(gref->page),
                                                 readonly);
                if (rc < 0)
                        goto undo;
                gref_ids[i] = gref->gref_id = rc;
        }

        /* Add to gref lists. */
        mutex_lock(&gref_mutex);
        list_splice_tail(&queue_gref, &gref_list);
        list_splice_tail(&queue_file, &priv->list);
        mutex_unlock(&gref_mutex);

        return 0;

undo:
        mutex_lock(&gref_mutex);
        gref_size -= (op->count - i);

        list_for_each_entry_safe(gref, next, &queue_file, next_file) {
                list_del(&gref->next_file);
                __del_gref(gref);
        }

        /* It's possible for the target domain to map the just-allocated grant
         * references by blindly guessing their IDs; if this is done, then
         * __del_gref will leave them in the queue_gref list. They need to be
         * added to the global list so that we can free them when they are no
         * longer referenced.
         */
        if (unlikely(!list_empty(&queue_gref)))
                list_splice_tail(&queue_gref, &gref_list);
        mutex_unlock(&gref_mutex);
        return rc;
}

static void __del_gref(struct gntalloc_gref *gref)
{
        if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
                uint8_t *tmp = kmap(gref->page);
                tmp[gref->notify.pgoff] = 0;
                kunmap(gref->page);
        }
        if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
                notify_remote_via_evtchn(gref->notify.event);
                evtchn_put(gref->notify.event);
        }

        gref->notify.flags = 0;

        if (gref->gref_id) {
                if (gnttab_query_foreign_access(gref->gref_id))
                        return;

                if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
                        return;

                gnttab_free_grant_reference(gref->gref_id);
        }

        gref_size--;
        list_del(&gref->next_gref);

        if (gref->page)
                __free_page(gref->page);

        kfree(gref);
}

/* finds contiguous grant references in a file, returns the first */
static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
                uint64_t index, uint32_t count)
{
        struct gntalloc_gref *rv = NULL, *gref;
        list_for_each_entry(gref, &priv->list, next_file) {
                if (gref->file_index == index && !rv)
                        rv = gref;
                if (rv) {
                        if (gref->file_index != index)
                                return NULL;
                        index += PAGE_SIZE;
                        count--;
                        if (count == 0)
                                return rv;
                }
        }
        return NULL;
}

/*
 * -------------------------------------
 *  File operations.
 * -------------------------------------
 */
static int gntalloc_open(struct inode *inode, struct file *filp)
{
        struct gntalloc_file_private_data *priv;

        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
        if (!priv)
                goto out_nomem;
        INIT_LIST_HEAD(&priv->list);

        filp->private_data = priv;

        pr_debug("%s: priv %p\n", __func__, priv);

        return 0;

out_nomem:
        return -ENOMEM;
}

static int gntalloc_release(struct inode *inode, struct file *filp)
{
        struct gntalloc_file_private_data *priv = filp->private_data;
        struct gntalloc_gref *gref;

        pr_debug("%s: priv %p\n", __func__, priv);

        mutex_lock(&gref_mutex);
        while (!list_empty(&priv->list)) {
                gref = list_entry(priv->list.next,
                        struct gntalloc_gref, next_file);
                list_del(&gref->next_file);
                gref->users--;
                if (gref->users == 0)
                        __del_gref(gref);
        }
        kfree(priv);
        mutex_unlock(&gref_mutex);

        return 0;
}

static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
                struct ioctl_gntalloc_alloc_gref __user *arg)
{
        int rc = 0;
        struct ioctl_gntalloc_alloc_gref op;
        uint32_t *gref_ids;

        pr_debug("%s: priv %p\n", __func__, priv);

        if (copy_from_user(&op, arg, sizeof(op))) {
                rc = -EFAULT;
                goto out;
        }

        gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_KERNEL);
        if (!gref_ids) {
                rc = -ENOMEM;
                goto out;
        }

        mutex_lock(&gref_mutex);
        /* Clean up pages that were at zero (local) users but were still mapped
         * by remote domains. Since those pages count towards the limit that we
         * are about to enforce, removing them here is a good idea.
         */
        do_cleanup();
        if (gref_size + op.count > limit) {
                mutex_unlock(&gref_mutex);
                rc = -ENOSPC;
                goto out_free;
        }
        gref_size += op.count;
        op.index = priv->index;
        priv->index += op.count * PAGE_SIZE;
        mutex_unlock(&gref_mutex);

        rc = add_grefs(&op, gref_ids, priv);
        if (rc < 0)
                goto out_free;

        /* Once we finish add_grefs, it is unsafe to touch the new reference,
         * since it is possible for a concurrent ioctl to remove it (by guessing
         * its index). If the userspace application doesn't provide valid memory
         * to write the IDs to, then it will need to close the file in order to
         * release - which it will do by segfaulting when it tries to access the
         * IDs to close them.
         */
        if (copy_to_user(arg, &op, sizeof(op))) {
                rc = -EFAULT;
                goto out_free;
        }
        if (copy_to_user(arg->gref_ids, gref_ids,
                        sizeof(gref_ids[0]) * op.count)) {
                rc = -EFAULT;
                goto out_free;
        }

out_free:
        kfree(gref_ids);
out:
        return rc;
}

static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
                void __user *arg)
{
        int i, rc = 0;
        struct ioctl_gntalloc_dealloc_gref op;
        struct gntalloc_gref *gref, *n;

        pr_debug("%s: priv %p\n", __func__, priv);

        if (copy_from_user(&op, arg, sizeof(op))) {
                rc = -EFAULT;
                goto dealloc_grant_out;
        }

        mutex_lock(&gref_mutex);
        gref = find_grefs(priv, op.index, op.count);
        if (gref) {
                /* Remove from the file list only, and decrease reference count.
                 * The later call to do_cleanup() will remove from gref_list and
                 * free the memory if the pages aren't mapped anywhere.
                 */
                for (i = 0; i < op.count; i++) {
                        n = list_entry(gref->next_file.next,
                                struct gntalloc_gref, next_file);
                        list_del(&gref->next_file);
                        gref->users--;
                        gref = n;
                }
        } else {
                rc = -EINVAL;
        }

        do_cleanup();

        mutex_unlock(&gref_mutex);
dealloc_grant_out:
        return rc;
}

static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
                void __user *arg)
{
        struct ioctl_gntalloc_unmap_notify op;
        struct gntalloc_gref *gref;
        uint64_t index;
        int pgoff;
        int rc;

        if (copy_from_user(&op, arg, sizeof(op)))
                return -EFAULT;

        index = op.index & ~(PAGE_SIZE - 1);
        pgoff = op.index & (PAGE_SIZE - 1);

        mutex_lock(&gref_mutex);

        gref = find_grefs(priv, index, 1);
        if (!gref) {
                rc = -ENOENT;
                goto unlock_out;
        }

        if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
                rc = -EINVAL;
                goto unlock_out;
        }

        /* We need to grab a reference to the event channel we are going to use
         * to send the notify before releasing the reference we may already have
         * (if someone has called this ioctl twice). This is required so that
         * it is possible to change the clear_byte part of the notification
         * without disturbing the event channel part, which may now be the last
         * reference to that event channel.
         */
        if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
                if (evtchn_get(op.event_channel_port)) {
                        rc = -EINVAL;
                        goto unlock_out;
                }
        }

        if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
                evtchn_put(gref->notify.event);

        gref->notify.flags = op.action;
        gref->notify.pgoff = pgoff;
        gref->notify.event = op.event_channel_port;
        rc = 0;

 unlock_out:
        mutex_unlock(&gref_mutex);
        return rc;
}

static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
                unsigned long arg)
{
        struct gntalloc_file_private_data *priv = filp->private_data;

        switch (cmd) {
        case IOCTL_GNTALLOC_ALLOC_GREF:
                return gntalloc_ioctl_alloc(priv, (void __user *)arg);

        case IOCTL_GNTALLOC_DEALLOC_GREF:
                return gntalloc_ioctl_dealloc(priv, (void __user *)arg);

        case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
                return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);

        default:
                return -ENOIOCTLCMD;
        }

        return 0;
}

static void gntalloc_vma_open(struct vm_area_struct *vma)
{
        struct gntalloc_vma_private_data *priv = vma->vm_private_data;

        if (!priv)
                return;

        mutex_lock(&gref_mutex);
        priv->users++;
        mutex_unlock(&gref_mutex);
}

static void gntalloc_vma_close(struct vm_area_struct *vma)
{
        struct gntalloc_vma_private_data *priv = vma->vm_private_data;
        struct gntalloc_gref *gref, *next;
        int i;

        if (!priv)
                return;

        mutex_lock(&gref_mutex);
        priv->users--;
        if (priv->users == 0) {
                gref = priv->gref;
                for (i = 0; i < priv->count; i++) {
                        gref->users--;
                        next = list_entry(gref->next_gref.next,
                                          struct gntalloc_gref, next_gref);
                        if (gref->users == 0)
                                __del_gref(gref);
                        gref = next;
                }
                kfree(priv);
        }
        mutex_unlock(&gref_mutex);
}

static const struct vm_operations_struct gntalloc_vmops = {
        .open = gntalloc_vma_open,
        .close = gntalloc_vma_close,
};

static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
{
        struct gntalloc_file_private_data *priv = filp->private_data;
        struct gntalloc_vma_private_data *vm_priv;
        struct gntalloc_gref *gref;
        int count = vma_pages(vma);
        int rv, i;

        if (!(vma->vm_flags & VM_SHARED)) {
                pr_err("%s: Mapping must be shared\n", __func__);
                return -EINVAL;
        }

        vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
        if (!vm_priv)
                return -ENOMEM;

        mutex_lock(&gref_mutex);

        pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,
                       priv, vm_priv, vma->vm_pgoff, count);

        gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
        if (gref == NULL) {
                rv = -ENOENT;
                pr_debug("%s: Could not find grant reference",
                                __func__);
                kfree(vm_priv);
                goto out_unlock;
        }

        vm_priv->gref = gref;
        vm_priv->users = 1;
        vm_priv->count = count;

        vma->vm_private_data = vm_priv;

        vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;

        vma->vm_ops = &gntalloc_vmops;

        for (i = 0; i < count; i++) {
                gref->users++;
                rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
                                gref->page);
                if (rv)
                        goto out_unlock;

                gref = list_entry(gref->next_file.next,
                                struct gntalloc_gref, next_file);
        }
        rv = 0;

out_unlock:
        mutex_unlock(&gref_mutex);
        return rv;
}

static const struct file_operations gntalloc_fops = {
        .owner = THIS_MODULE,
        .open = gntalloc_open,
        .release = gntalloc_release,
        .unlocked_ioctl = gntalloc_ioctl,
        .mmap = gntalloc_mmap
};

/*
 * -------------------------------------
 * Module creation/destruction.
 * -------------------------------------
 */
static struct miscdevice gntalloc_miscdev = {
        .minor  = MISC_DYNAMIC_MINOR,
        .name   = "xen/gntalloc",
        .fops   = &gntalloc_fops,
};

static int __init gntalloc_init(void)
{
        int err;

        if (!xen_domain())
                return -ENODEV;

        err = misc_register(&gntalloc_miscdev);
        if (err != 0) {
                pr_err("Could not register misc gntalloc device\n");
                return err;
        }

        pr_debug("Created grant allocation device at %d,%d\n",
                        MISC_MAJOR, gntalloc_miscdev.minor);

        return 0;
}

static void __exit gntalloc_exit(void)
{
        misc_deregister(&gntalloc_miscdev);
}

module_init(gntalloc_init);
module_exit(gntalloc_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
                "Daniel De Graaf <dgdegra@tycho.nsa.gov>");
MODULE_DESCRIPTION("User-space grant reference allocator driver");