1 files changed, 765 insertions, 0 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
new file mode 100644
index 000000000000..f914b26cf0c2
--- /dev/null
+++ b/drivers/xen/gntdev.c
@@ -0,0 +1,765 @@
+/******************************************************************************
+ * gntdev.c
+ *
+ * Device for accessing (in user-space) pages that have been granted by other
+ * domains.
+ *
+ * Copyright (c) 2006-2007, D G Murray.
+ *           (c) 2009 Gerd Hoffmann <kraxel@redhat.com>
+ *
+ * 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
+ */
+
+#undef DEBUG
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/miscdevice.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/mmu_notifier.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/highmem.h>
+
+#include <xen/xen.h>
+#include <xen/grant_table.h>
+#include <xen/balloon.h>
+#include <xen/gntdev.h>
+#include <xen/events.h>
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+#include <asm/xen/page.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Derek G. Murray <Derek.Murray@cl.cam.ac.uk>, "
+              "Gerd Hoffmann <kraxel@redhat.com>");
+MODULE_DESCRIPTION("User-space granted page access driver");
+
+static int limit = 1024*1024;
+module_param(limit, int, 0644);
+MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped by "
+                "the gntdev device");
+
+static atomic_t pages_mapped = ATOMIC_INIT(0);
+
+static int use_ptemod;
+
+struct gntdev_priv {
+        struct list_head maps;
+        /* lock protects maps from concurrent changes */
+        spinlock_t lock;
+        struct mm_struct *mm;
+        struct mmu_notifier mn;
+};
+
+struct unmap_notify {
+        int flags;
+        /* Address relative to the start of the grant_map */
+        int addr;
+        int event;
+};
+
+struct grant_map {
+        struct list_head next;
+        struct vm_area_struct *vma;
+        int index;
+        int count;
+        int flags;
+        atomic_t users;
+        struct unmap_notify notify;
+        struct ioctl_gntdev_grant_ref *grants;
+        struct gnttab_map_grant_ref   *map_ops;
+        struct gnttab_unmap_grant_ref *unmap_ops;
+        struct page **pages;
+};
+
+static int unmap_grant_pages(struct grant_map *map, int offset, int pages);
+
+/* ------------------------------------------------------------------ */
+
+static void gntdev_print_maps(struct gntdev_priv *priv,
+                              char *text, int text_index)
+{
+#ifdef DEBUG
+        struct grant_map *map;
+
+        pr_debug("%s: maps list (priv %p)\n", __func__, priv);
+        list_for_each_entry(map, &priv->maps, next)
+                pr_debug("  index %2d, count %2d %s\n",
+                       map->index, map->count,
+                       map->index == text_index && text ? text : "");
+#endif
+}
+
+static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
+{
+        struct grant_map *add;
+        int i;
+
+        add = kzalloc(sizeof(struct grant_map), GFP_KERNEL);
+        if (NULL == add)
+                return NULL;
+
+        add->grants    = kzalloc(sizeof(add->grants[0])    * count, GFP_KERNEL);
+        add->map_ops   = kzalloc(sizeof(add->map_ops[0])   * count, GFP_KERNEL);
+        add->unmap_ops = kzalloc(sizeof(add->unmap_ops[0]) * count, GFP_KERNEL);
+        add->pages     = kzalloc(sizeof(add->pages[0])     * count, GFP_KERNEL);
+        if (NULL == add->grants    ||
+            NULL == add->map_ops   ||
+            NULL == add->unmap_ops ||
+            NULL == add->pages)
+                goto err;
+
+        if (alloc_xenballooned_pages(count, add->pages))
+                goto err;
+
+        for (i = 0; i < count; i++) {
+                add->map_ops[i].handle = -1;
+                add->unmap_ops[i].handle = -1;
+        }
+
+        add->index = 0;
+        add->count = count;
+        atomic_set(&add->users, 1);
+
+        return add;
+
+err:
+        kfree(add->pages);
+        kfree(add->grants);
+        kfree(add->map_ops);
+        kfree(add->unmap_ops);
+        kfree(add);
+        return NULL;
+}
+
+static void gntdev_add_map(struct gntdev_priv *priv, struct grant_map *add)
+{
+        struct grant_map *map;
+
+        list_for_each_entry(map, &priv->maps, next) {
+                if (add->index + add->count < map->index) {
+                        list_add_tail(&add->next, &map->next);
+                        goto done;
+                }
+                add->index = map->index + map->count;
+        }
+        list_add_tail(&add->next, &priv->maps);
+
+done:
+        gntdev_print_maps(priv, "[new]", add->index);
+}
+
+static struct grant_map *gntdev_find_map_index(struct gntdev_priv *priv,
+                int index, int count)
+{
+        struct grant_map *map;
+
+        list_for_each_entry(map, &priv->maps, next) {
+                if (map->index != index)
+                        continue;
+                if (count && map->count != count)
+                        continue;
+                return map;
+        }
+        return NULL;
+}
+
+static void gntdev_put_map(struct grant_map *map)
+{
+        if (!map)
+                return;
+
+        if (!atomic_dec_and_test(&map->users))
+                return;
+
+        atomic_sub(map->count, &pages_mapped);
+
+        if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
+                notify_remote_via_evtchn(map->notify.event);
+        }
+
+        if (map->pages) {
+                if (!use_ptemod)
+                        unmap_grant_pages(map, 0, map->count);
+
+                free_xenballooned_pages(map->count, map->pages);
+        }
+        kfree(map->pages);
+        kfree(map->grants);
+        kfree(map->map_ops);
+        kfree(map->unmap_ops);
+        kfree(map);
+}
+
+/* ------------------------------------------------------------------ */
+
+static int find_grant_ptes(pte_t *pte, pgtable_t token,
+                unsigned long addr, void *data)
+{
+        struct grant_map *map = data;
+        unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT;
+        int flags = map->flags | GNTMAP_application_map | GNTMAP_contains_pte;
+        u64 pte_maddr;
+
+        BUG_ON(pgnr >= map->count);
+        pte_maddr = arbitrary_virt_to_machine(pte).maddr;
+
+        gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, flags,
+                          map->grants[pgnr].ref,
+                          map->grants[pgnr].domid);
+        gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr, flags,
+                            -1 /* handle */);
+        return 0;
+}
+
+static int map_grant_pages(struct grant_map *map)
+{
+        int i, err = 0;
+
+        if (!use_ptemod) {
+                /* Note: it could already be mapped */
+                if (map->map_ops[0].handle != -1)
+                        return 0;
+                for (i = 0; i < map->count; i++) {
+                        unsigned long addr = (unsigned long)
+                                pfn_to_kaddr(page_to_pfn(map->pages[i]));
+                        gnttab_set_map_op(&map->map_ops[i], addr, map->flags,
+                                map->grants[i].ref,
+                                map->grants[i].domid);
+                        gnttab_set_unmap_op(&map->unmap_ops[i], addr,
+                                map->flags, -1 /* handle */);
+                }
+        }
+
+        pr_debug("map %d+%d\n", map->index, map->count);
+        err = gnttab_map_refs(map->map_ops, map->pages, map->count);
+        if (err)
+                return err;
+
+        for (i = 0; i < map->count; i++) {
+                if (map->map_ops[i].status)
+                        err = -EINVAL;
+                else {
+                        BUG_ON(map->map_ops[i].handle == -1);
+                        map->unmap_ops[i].handle = map->map_ops[i].handle;
+                        pr_debug("map handle=%d\n", map->map_ops[i].handle);
+                }
+        }
+        return err;
+}
+
+static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
+{
+        int i, err = 0;
+
+        if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
+                int pgno = (map->notify.addr >> PAGE_SHIFT);
+                if (pgno >= offset && pgno < offset + pages && use_ptemod) {
+                        void __user *tmp = (void __user *)
+                                map->vma->vm_start + map->notify.addr;
+                        err = copy_to_user(tmp, &err, 1);
+                        if (err)
+                                return -EFAULT;
+                        map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
+                } else if (pgno >= offset && pgno < offset + pages) {
+                        uint8_t *tmp = kmap(map->pages[pgno]);
+                        tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
+                        kunmap(map->pages[pgno]);
+                        map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
+                }
+        }
+
+        err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages + offset, pages);
+        if (err)
+                return err;
+
+        for (i = 0; i < pages; i++) {
+                if (map->unmap_ops[offset+i].status)
+                        err = -EINVAL;
+                pr_debug("unmap handle=%d st=%d\n",
+                        map->unmap_ops[offset+i].handle,
+                        map->unmap_ops[offset+i].status);
+                map->unmap_ops[offset+i].handle = -1;
+        }
+        return err;
+}
+
+static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
+{
+        int range, err = 0;
+
+        pr_debug("unmap %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
+
+        /* It is possible the requested range will have a "hole" where we
+         * already unmapped some of the grants. Only unmap valid ranges.
+         */
+        while (pages && !err) {
+                while (pages && map->unmap_ops[offset].handle == -1) {
+                        offset++;
+                        pages--;
+                }
+                range = 0;
+                while (range < pages) {
+                        if (map->unmap_ops[offset+range].handle == -1) {
+                                range--;
+                                break;
+                        }
+                        range++;
+                }
+                err = __unmap_grant_pages(map, offset, range);
+                offset += range;
+                pages -= range;
+        }
+
+        return err;
+}
+
+/* ------------------------------------------------------------------ */
+
+static void gntdev_vma_open(struct vm_area_struct *vma)
+{
+        struct grant_map *map = vma->vm_private_data;
+
+        pr_debug("gntdev_vma_open %p\n", vma);
+        atomic_inc(&map->users);
+}
+
+static void gntdev_vma_close(struct vm_area_struct *vma)
+{
+        struct grant_map *map = vma->vm_private_data;
+
+        pr_debug("gntdev_vma_close %p\n", vma);
+        map->vma = NULL;
+        vma->vm_private_data = NULL;
+        gntdev_put_map(map);
+}
+
+static struct vm_operations_struct gntdev_vmops = {
+        .open = gntdev_vma_open,
+        .close = gntdev_vma_close,
+};
+
+/* ------------------------------------------------------------------ */
+
+static void mn_invl_range_start(struct mmu_notifier *mn,
+                                struct mm_struct *mm,
+                                unsigned long start, unsigned long end)
+{
+        struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
+        struct grant_map *map;
+        unsigned long mstart, mend;
+        int err;
+
+        spin_lock(&priv->lock);
+        list_for_each_entry(map, &priv->maps, next) {
+                if (!map->vma)
+                        continue;
+                if (map->vma->vm_start >= end)
+                        continue;
+                if (map->vma->vm_end <= start)
+                        continue;
+                mstart = max(start, map->vma->vm_start);
+                mend   = min(end,   map->vma->vm_end);
+                pr_debug("map %d+%d (%lx %lx), range %lx %lx, mrange %lx %lx\n",
+                                map->index, map->count,
+                                map->vma->vm_start, map->vma->vm_end,
+                                start, end, mstart, mend);
+                err = unmap_grant_pages(map,
+                                        (mstart - map->vma->vm_start) >> PAGE_SHIFT,
+                                        (mend - mstart) >> PAGE_SHIFT);
+                WARN_ON(err);
+        }
+        spin_unlock(&priv->lock);
+}
+
+static void mn_invl_page(struct mmu_notifier *mn,
+                         struct mm_struct *mm,
+                         unsigned long address)
+{
+        mn_invl_range_start(mn, mm, address, address + PAGE_SIZE);
+}
+
+static void mn_release(struct mmu_notifier *mn,
+                       struct mm_struct *mm)
+{
+        struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
+        struct grant_map *map;
+        int err;
+
+        spin_lock(&priv->lock);
+        list_for_each_entry(map, &priv->maps, next) {
+                if (!map->vma)
+                        continue;
+                pr_debug("map %d+%d (%lx %lx)\n",
+                                map->index, map->count,
+                                map->vma->vm_start, map->vma->vm_end);
+                err = unmap_grant_pages(map, /* offset */ 0, map->count);
+                WARN_ON(err);
+        }
+        spin_unlock(&priv->lock);
+}
+
+struct mmu_notifier_ops gntdev_mmu_ops = {
+        .release                = mn_release,
+        .invalidate_page        = mn_invl_page,
+        .invalidate_range_start = mn_invl_range_start,
+};
+
+/* ------------------------------------------------------------------ */
+
+static int gntdev_open(struct inode *inode, struct file *flip)
+{
+        struct gntdev_priv *priv;
+        int ret = 0;
+
+        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+        if (!priv)
+                return -ENOMEM;
+
+        INIT_LIST_HEAD(&priv->maps);
+        spin_lock_init(&priv->lock);
+
+        if (use_ptemod) {
+                priv->mm = get_task_mm(current);
+                if (!priv->mm) {
+                        kfree(priv);
+                        return -ENOMEM;
+                }
+                priv->mn.ops = &gntdev_mmu_ops;
+                ret = mmu_notifier_register(&priv->mn, priv->mm);
+                mmput(priv->mm);
+        }
+
+        if (ret) {
+                kfree(priv);
+                return ret;
+        }
+
+        flip->private_data = priv;
+        pr_debug("priv %p\n", priv);
+
+        return 0;
+}
+
+static int gntdev_release(struct inode *inode, struct file *flip)
+{
+        struct gntdev_priv *priv = flip->private_data;
+        struct grant_map *map;
+
+        pr_debug("priv %p\n", priv);
+
+        spin_lock(&priv->lock);
+        while (!list_empty(&priv->maps)) {
+                map = list_entry(priv->maps.next, struct grant_map, next);
+                list_del(&map->next);
+                gntdev_put_map(map);
+        }
+        spin_unlock(&priv->lock);
+
+        if (use_ptemod)
+                mmu_notifier_unregister(&priv->mn, priv->mm);
+        kfree(priv);
+        return 0;
+}
+
+static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,
+                                       struct ioctl_gntdev_map_grant_ref __user *u)
+{
+        struct ioctl_gntdev_map_grant_ref op;
+        struct grant_map *map;
+        int err;
+
+        if (copy_from_user(&op, u, sizeof(op)) != 0)
+                return -EFAULT;
+        pr_debug("priv %p, add %d\n", priv, op.count);
+        if (unlikely(op.count <= 0))
+                return -EINVAL;
+
+        err = -ENOMEM;
+        map = gntdev_alloc_map(priv, op.count);
+        if (!map)
+                return err;
+
+        if (unlikely(atomic_add_return(op.count, &pages_mapped) > limit)) {
+                pr_debug("can't map: over limit\n");
+                gntdev_put_map(map);
+                return err;
+        }
+
+        if (copy_from_user(map->grants, &u->refs,
+                           sizeof(map->grants[0]) * op.count) != 0) {
+                gntdev_put_map(map);
+                return err;
+        }
+
+        spin_lock(&priv->lock);
+        gntdev_add_map(priv, map);
+        op.index = map->index << PAGE_SHIFT;
+        spin_unlock(&priv->lock);
+
+        if (copy_to_user(u, &op, sizeof(op)) != 0)
+                return -EFAULT;
+
+        return 0;
+}
+
+static long gntdev_ioctl_unmap_grant_ref(struct gntdev_priv *priv,
+                                         struct ioctl_gntdev_unmap_grant_ref __user *u)
+{
+        struct ioctl_gntdev_unmap_grant_ref op;
+        struct grant_map *map;
+        int err = -ENOENT;
+
+        if (copy_from_user(&op, u, sizeof(op)) != 0)
+                return -EFAULT;
+        pr_debug("priv %p, del %d+%d\n", priv, (int)op.index, (int)op.count);
+
+        spin_lock(&priv->lock);
+        map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
+        if (map) {
+                list_del(&map->next);
+                gntdev_put_map(map);
+                err = 0;
+        }
+        spin_unlock(&priv->lock);
+        return err;
+}
+
+static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
+                                              struct ioctl_gntdev_get_offset_for_vaddr __user *u)
+{
+        struct ioctl_gntdev_get_offset_for_vaddr op;
+        struct vm_area_struct *vma;
+        struct grant_map *map;
+
+        if (copy_from_user(&op, u, sizeof(op)) != 0)
+                return -EFAULT;
+        pr_debug("priv %p, offset for vaddr %lx\n", priv, (unsigned long)op.vaddr);
+
+        vma = find_vma(current->mm, op.vaddr);
+        if (!vma || vma->vm_ops != &gntdev_vmops)
+                return -EINVAL;
+
+        map = vma->vm_private_data;
+        if (!map)
+                return -EINVAL;
+
+        op.offset = map->index << PAGE_SHIFT;
+        op.count = map->count;
+
+        if (copy_to_user(u, &op, sizeof(op)) != 0)
+                return -EFAULT;
+        return 0;
+}
+
+static long gntdev_ioctl_notify(struct gntdev_priv *priv, void __user *u)
+{
+        struct ioctl_gntdev_unmap_notify op;
+        struct grant_map *map;
+        int rc;
+
+        if (copy_from_user(&op, u, sizeof(op)))
+                return -EFAULT;
+
+        if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT))
+                return -EINVAL;
+
+        spin_lock(&priv->lock);
+
+        list_for_each_entry(map, &priv->maps, next) {
+                uint64_t begin = map->index << PAGE_SHIFT;
+                uint64_t end = (map->index + map->count) << PAGE_SHIFT;
+                if (op.index >= begin && op.index < end)
+                        goto found;
+        }
+        rc = -ENOENT;
+        goto unlock_out;
+
+ found:
+        if ((op.action & UNMAP_NOTIFY_CLEAR_BYTE) &&
+                        (map->flags & GNTMAP_readonly)) {
+                rc = -EINVAL;
+                goto unlock_out;
+        }
+
+        map->notify.flags = op.action;
+        map->notify.addr = op.index - (map->index << PAGE_SHIFT);
+        map->notify.event = op.event_channel_port;
+        rc = 0;
+ unlock_out:
+        spin_unlock(&priv->lock);
+        return rc;
+}
+
+static long gntdev_ioctl(struct file *flip,
+                         unsigned int cmd, unsigned long arg)
+{
+        struct gntdev_priv *priv = flip->private_data;
+        void __user *ptr = (void __user *)arg;
+
+        switch (cmd) {
+        case IOCTL_GNTDEV_MAP_GRANT_REF:
+                return gntdev_ioctl_map_grant_ref(priv, ptr);
+
+        case IOCTL_GNTDEV_UNMAP_GRANT_REF:
+                return gntdev_ioctl_unmap_grant_ref(priv, ptr);
+
+        case IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR:
+                return gntdev_ioctl_get_offset_for_vaddr(priv, ptr);
+
+        case IOCTL_GNTDEV_SET_UNMAP_NOTIFY:
+                return gntdev_ioctl_notify(priv, ptr);
+
+        default:
+                pr_debug("priv %p, unknown cmd %x\n", priv, cmd);
+                return -ENOIOCTLCMD;
+        }
+
+        return 0;
+}
+
+static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
+{
+        struct gntdev_priv *priv = flip->private_data;
+        int index = vma->vm_pgoff;
+        int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+        struct grant_map *map;
+        int i, err = -EINVAL;
+
+        if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
+                return -EINVAL;
+
+        pr_debug("map %d+%d at %lx (pgoff %lx)\n",
+                        index, count, vma->vm_start, vma->vm_pgoff);
+
+        spin_lock(&priv->lock);
+        map = gntdev_find_map_index(priv, index, count);
+        if (!map)
+                goto unlock_out;
+        if (use_ptemod && map->vma)
+                goto unlock_out;
+        if (use_ptemod && priv->mm != vma->vm_mm) {
+                printk(KERN_WARNING "Huh? Other mm?\n");
+                goto unlock_out;
+        }
+
+        atomic_inc(&map->users);
+
+        vma->vm_ops = &gntdev_vmops;
+
+        vma->vm_flags |= VM_RESERVED|VM_DONTEXPAND;
+
+        if (use_ptemod)
+                vma->vm_flags |= VM_DONTCOPY|VM_PFNMAP;
+
+        vma->vm_private_data = map;
+
+        if (use_ptemod)
+                map->vma = vma;
+
+        if (map->flags) {
+                if ((vma->vm_flags & VM_WRITE) &&
+                                (map->flags & GNTMAP_readonly))
+                        goto out_unlock_put;
+        } else {
+                map->flags = GNTMAP_host_map;
+                if (!(vma->vm_flags & VM_WRITE))
+                        map->flags |= GNTMAP_readonly;
+        }
+
+        spin_unlock(&priv->lock);
+
+        if (use_ptemod) {
+                err = apply_to_page_range(vma->vm_mm, vma->vm_start,
+                                          vma->vm_end - vma->vm_start,
+                                          find_grant_ptes, map);
+                if (err) {
+                        printk(KERN_WARNING "find_grant_ptes() failure.\n");
+                        goto out_put_map;
+                }
+        }
+
+        err = map_grant_pages(map);
+        if (err)
+                goto out_put_map;
+
+        if (!use_ptemod) {
+                for (i = 0; i < count; i++) {
+                        err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
+                                map->pages[i]);
+                        if (err)
+                                goto out_put_map;
+                }
+        }
+
+        return 0;
+
+unlock_out:
+        spin_unlock(&priv->lock);
+        return err;
+
+out_unlock_put:
+        spin_unlock(&priv->lock);
+out_put_map:
+        if (use_ptemod)
+                map->vma = NULL;
+        gntdev_put_map(map);
+        return err;
+}
+
+static const struct file_operations gntdev_fops = {
+        .owner = THIS_MODULE,
+        .open = gntdev_open,
+        .release = gntdev_release,
+        .mmap = gntdev_mmap,
+        .unlocked_ioctl = gntdev_ioctl
+};
+
+static struct miscdevice gntdev_miscdev = {
+        .minor        = MISC_DYNAMIC_MINOR,
+        .name         = "xen/gntdev",
+        .fops         = &gntdev_fops,
+};
+
+/* ------------------------------------------------------------------ */
+
+static int __init gntdev_init(void)
+{
+        int err;
+
+        if (!xen_domain())
+                return -ENODEV;
+
+        use_ptemod = xen_pv_domain();
+
+        err = misc_register(&gntdev_miscdev);
+        if (err != 0) {
+                printk(KERN_ERR "Could not register gntdev device\n");
+                return err;
+        }
+        return 0;
+}
+
+static void __exit gntdev_exit(void)
+{
+        misc_deregister(&gntdev_miscdev);
+}
+
+module_init(gntdev_init);
+module_exit(gntdev_exit);
+
+/* ------------------------------------------------------------------ */