/******************************************************************************
 * 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

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

#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 <xen/page.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.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;
#define populate_freeable_maps use_ptemod

struct gntdev_priv {
        /* maps with visible offsets in the file descriptor */
        struct list_head maps;
        /* maps that are not visible; will be freed on munmap.
         * Only populated if populate_freeable_maps == 1 */
        struct list_head freeable_maps;
        /* lock protects maps and freeable_maps */
        struct mutex 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 gnttab_map_grant_ref   *kmap_ops;
        struct gnttab_unmap_grant_ref *kunmap_ops;
        struct page **pages;
        unsigned long pages_vm_start;
};

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 void gntdev_free_map(struct grant_map *map)
{
        if (map == NULL)
                return;

        if (map->pages)
                gnttab_free_pages(map->count, map->pages);
        kfree(map->pages);
        kfree(map->grants);
        kfree(map->map_ops);
        kfree(map->unmap_ops);
        kfree(map->kmap_ops);
        kfree(map->kunmap_ops);
        kfree(map);
}

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    = kcalloc(count, sizeof(add->grants[0]), GFP_KERNEL);
        add->map_ops   = kcalloc(count, sizeof(add->map_ops[0]), GFP_KERNEL);
        add->unmap_ops = kcalloc(count, sizeof(add->unmap_ops[0]), GFP_KERNEL);
        add->kmap_ops  = kcalloc(count, sizeof(add->kmap_ops[0]), GFP_KERNEL);
        add->kunmap_ops = kcalloc(count, sizeof(add->kunmap_ops[0]), GFP_KERNEL);
        add->pages     = kcalloc(count, sizeof(add->pages[0]), GFP_KERNEL);
        if (NULL == add->grants    ||
            NULL == add->map_ops   ||
            NULL == add->unmap_ops ||
            NULL == add->kmap_ops  ||
            NULL == add->kunmap_ops ||
            NULL == add->pages)
                goto err;

        if (gnttab_alloc_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->kmap_ops[i].handle = -1;
                add->kunmap_ops[i].handle = -1;
        }

        add->index = 0;
        add->count = count;
        atomic_set(&add->users, 1);

        return add;

err:
        gntdev_free_map(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 gntdev_priv *priv, 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);
                evtchn_put(map->notify.event);
        }

        if (populate_freeable_maps && priv) {
                mutex_lock(&priv->lock);
                list_del(&map->next);
                mutex_unlock(&priv->lock);
        }

        if (map->pages && !use_ptemod)
                unmap_grant_pages(map, 0, map->count);
        gntdev_free_map(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;

        /*
         * Set the PTE as special to force get_user_pages_fast() fall
         * back to the slow path.  If this is not supported as part of
         * the grant map, it will be done afterwards.
         */
        if (xen_feature(XENFEAT_gnttab_map_avail_bits))
                flags |= (1 << _GNTMAP_guest_avail0);

        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;
}

#ifdef CONFIG_X86
static int set_grant_ptes_as_special(pte_t *pte, pgtable_t token,
                                     unsigned long addr, void *data)
{
        set_pte_at(current->mm, addr, pte, pte_mkspecial(*pte));
        return 0;
}
#endif

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 */);
                }
        } else {
                /*
                 * Setup the map_ops corresponding to the pte entries pointing
                 * to the kernel linear addresses of the struct pages.
                 * These ptes are completely different from the user ptes dealt
                 * with find_grant_ptes.
                 */
                for (i = 0; i < map->count; i++) {
                        unsigned long address = (unsigned long)
                                pfn_to_kaddr(page_to_pfn(map->pages[i]));
                        BUG_ON(PageHighMem(map->pages[i]));

                        gnttab_set_map_op(&map->kmap_ops[i], address,
                                map->flags | GNTMAP_host_map,
                                map->grants[i].ref,
                                map->grants[i].domid);
                        gnttab_set_unmap_op(&map->kunmap_ops[i], address,
                                map->flags | GNTMAP_host_map, -1);
                }
        }

        pr_debug("map %d+%d\n", map->index, map->count);
        err = gnttab_map_refs(map->map_ops, use_ptemod ? map->kmap_ops : NULL,
                        map->pages, map->count);
        if (err)
                return err;

        for (i = 0; i < map->count; i++) {
                if (map->map_ops[i].status) {
                        err = -EINVAL;
                        continue;
                }

                map->unmap_ops[i].handle = map->map_ops[i].handle;
                if (use_ptemod)
                        map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
        }
        return err;
}

static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
{
        int i, err = 0;
        struct gntab_unmap_queue_data unmap_data;

        if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
                int pgno = (map->notify.addr >> PAGE_SHIFT);
                if (pgno >= offset && pgno < offset + pages) {
                        /* No need for kmap, pages are in lowmem */
                        uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
                        tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
                        map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
                }
        }

        unmap_data.unmap_ops = map->unmap_ops + offset;
        unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
        unmap_data.pages = map->pages + offset;
        unmap_data.count = pages;

        err = gnttab_unmap_refs_sync(&unmap_data);
        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;
        struct file *file = vma->vm_file;
        struct gntdev_priv *priv = file->private_data;

        pr_debug("gntdev_vma_close %p\n", vma);
        if (use_ptemod) {
                /* It is possible that an mmu notifier could be running
                 * concurrently, so take priv->lock to ensure that the vma won't
                 * vanishing during the unmap_grant_pages call, since we will
                 * spin here until that completes. Such a concurrent call will
                 * not do any unmapping, since that has been done prior to
                 * closing the vma, but it may still iterate the unmap_ops list.
                 */
                mutex_lock(&priv->lock);
                map->vma = NULL;
                mutex_unlock(&priv->lock);
        }
        vma->vm_private_data = NULL;
        gntdev_put_map(priv, map);
}

static struct page *gntdev_vma_find_special_page(struct vm_area_struct *vma,
                                                 unsigned long addr)
{
        struct grant_map *map = vma->vm_private_data;

        return map->pages[(addr - map->pages_vm_start) >> PAGE_SHIFT];
}

static const struct vm_operations_struct gntdev_vmops = {
        .open = gntdev_vma_open,
        .close = gntdev_vma_close,
        .find_special_page = gntdev_vma_find_special_page,
};

/* ------------------------------------------------------------------ */

static void unmap_if_in_range(struct grant_map *map,
                              unsigned long start, unsigned long end)
{
        unsigned long mstart, mend;
        int err;

        if (!map->vma)
                return;
        if (map->vma->vm_start >= end)
                return;
        if (map->vma->vm_end <= start)
                return;
        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);
}

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;

        mutex_lock(&priv->lock);
        list_for_each_entry(map, &priv->maps, next) {
                unmap_if_in_range(map, start, end);
        }
        list_for_each_entry(map, &priv->freeable_maps, next) {
                unmap_if_in_range(map, start, end);
        }
        mutex_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;

        mutex_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);
        }
        list_for_each_entry(map, &priv->freeable_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);
        }
        mutex_unlock(&priv->lock);
}

static 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);
        INIT_LIST_HEAD(&priv->freeable_maps);
        mutex_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);

        mutex_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(NULL /* already removed */, map);
        }
        WARN_ON(!list_empty(&priv->freeable_maps));
        mutex_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(NULL, map);
                return err;
        }

        if (copy_from_user(map->grants, &u->refs,
                           sizeof(map->grants[0]) * op.count) != 0) {
                gntdev_put_map(NULL, map);
                return -EFAULT;
        }

        mutex_lock(&priv->lock);
        gntdev_add_map(priv, map);
        op.index = map->index << PAGE_SHIFT;
        mutex_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);

        mutex_lock(&priv->lock);
        map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
        if (map) {
                list_del(&map->next);
                if (populate_freeable_maps)
                        list_add_tail(&map->next, &priv->freeable_maps);
                err = 0;
        }
        mutex_unlock(&priv->lock);
        if (map)
                gntdev_put_map(priv, map);
        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;
        int rv = -EINVAL;

        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);

        down_read(&current->mm->mmap_sem);
        vma = find_vma(current->mm, op.vaddr);
        if (!vma || vma->vm_ops != &gntdev_vmops)
                goto out_unlock;

        map = vma->vm_private_data;
        if (!map)
                goto out_unlock;

        op.offset = map->index << PAGE_SHIFT;
        op.count = map->count;
        rv = 0;

 out_unlock:
        up_read(&current->mm->mmap_sem);

        if (rv == 0 && copy_to_user(u, &op, sizeof(op)) != 0)
                return -EFAULT;
        return rv;
}

static long gntdev_ioctl_notify(struct gntdev_priv *priv, void __user *u)
{
        struct ioctl_gntdev_unmap_notify op;
        struct grant_map *map;
        int rc;
        int out_flags;
        unsigned int out_event;

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

        if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT))
                return -EINVAL;

        /* 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))
                        return -EINVAL;
        }

        out_flags = op.action;
        out_event = op.event_channel_port;

        mutex_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;
        }

        out_flags = map->notify.flags;
        out_event = map->notify.event;

        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:
        mutex_unlock(&priv->lock);

        /* Drop the reference to the event channel we did not save in the map */
        if (out_flags & UNMAP_NOTIFY_SEND_EVENT)
                evtchn_put(out_event);

        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);

        mutex_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) {
                pr_warn("Huh? Other mm?\n");
                goto unlock_out;
        }

        atomic_inc(&map->users);

        vma->vm_ops = &gntdev_vmops;

        vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;

        if (use_ptemod)
                vma->vm_flags |= VM_DONTCOPY;

        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;
        }

        mutex_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) {
                        pr_warn("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;
                }
        } else {
#ifdef CONFIG_X86
                /*
                 * If the PTEs were not made special by the grant map
                 * hypercall, do so here.
                 *
                 * This is racy since the mapping is already visible
                 * to userspace but userspace should be well-behaved
                 * enough to not touch it until the mmap() call
                 * returns.
                 */
                if (!xen_feature(XENFEAT_gnttab_map_avail_bits)) {
                        apply_to_page_range(vma->vm_mm, vma->vm_start,
                                            vma->vm_end - vma->vm_start,
                                            set_grant_ptes_as_special, NULL);
                }
#endif
                map->pages_vm_start = vma->vm_start;
        }

        return 0;

unlock_out:
        mutex_unlock(&priv->lock);
        return err;

out_unlock_put:
        mutex_unlock(&priv->lock);
out_put_map:
        if (use_ptemod)
                map->vma = NULL;
        gntdev_put_map(priv, 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_feature(XENFEAT_auto_translated_physmap);

        err = misc_register(&gntdev_miscdev);
        if (err != 0) {
                pr_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);

/* ------------------------------------------------------------------ */