gntdev.c

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/******************************************************************************
 * 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 <[email protected]>
 *
 * 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 <[email protected]>, "
          "Gerd Hoffmann <[email protected]>");
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 gnttab_map_grant_ref   *kmap_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 void gntdev_free_map(struct grant_map *map)
{
    if (map == NULL)
        return;

    if (map->pages)
        free_xenballooned_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);
}

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->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->pages)
        goto err;

    if (alloc_xenballooned_pages(count, add->pages, false /* lowmem */))
        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->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 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 (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;

    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 */);
        }
    } 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 level;
            unsigned long address = (unsigned long)
                pfn_to_kaddr(page_to_pfn(map->pages[i]));
            pte_t *ptep;
            u64 pte_maddr = 0;
            BUG_ON(PageHighMem(map->pages[i]));

            ptep = lookup_address(address, &level);
            pte_maddr = arbitrary_virt_to_machine(ptep).maddr;
            gnttab_set_map_op(&map->kmap_ops[i], pte_maddr,
                map->flags |
                GNTMAP_host_map |
                GNTMAP_contains_pte,
                map->grants[i].ref,
                map->grants[i].domid);
        }
    }

    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;
        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,
            use_ptemod ? map->kmap_ops + offset : NULL, 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);
}

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);
    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);

    while (!list_empty(&priv->maps)) {
        map = list_entry(priv->maps.next, struct grant_map, next);
        list_del(&map->next);
        gntdev_put_map(map);
    }

    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);
        err = 0;
    }
    spin_unlock(&priv->lock);
    if (map)
        gntdev_put_map(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;

    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;
    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;

    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;
    }

    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:
    spin_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);

    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_DONTEXPAND | VM_DONTDUMP;

    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;
    }

    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);

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