xen-gntdev: Change page limit to be global instead of per-open

Because there is no limitation on how many times a user can open a
given device file, an per-file-description limit on the number of
pages granted offers little to no benefit. Change to a global limit
and remove the ioctl() as the parameter can now be changed via sysfs.

Xen tools changeset 22768:f8d801e5573e is needed to eliminate the
error this change produces in xc_gnttab_set_max_grants.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 14 insertions, 36 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 1e31cdcdae1e..23d208a219fa 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -45,15 +45,15 @@ 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;
+static int limit = 1024*1024;
 module_param(limit, int, 0644);
-MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped at "
-                "once by a gntdev instance");
+MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped by "
+                "the gntdev device");
+
+static atomic_t pages_mapped = ATOMIC_INIT(0);
 
 struct gntdev_priv {
         struct list_head maps;
-        uint32_t used;
-        uint32_t limit;
         /* lock protects maps from concurrent changes */
         spinlock_t lock;
         struct mm_struct *mm;
@@ -82,9 +82,7 @@ static void gntdev_print_maps(struct gntdev_priv *priv,
 #ifdef DEBUG
         struct grant_map *map;
 
-        pr_debug("maps list (priv %p, usage %d/%d)\n",
-               priv, priv->used, priv->limit);
-
+        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,
@@ -121,9 +119,6 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
         add->count = count;
         add->priv  = priv;
 
-        if (add->count + priv->used > priv->limit)
-                goto err;
-
         return add;
 
 err:
@@ -154,7 +149,6 @@ static void gntdev_add_map(struct gntdev_priv *priv, struct grant_map *add)
         list_add_tail(&add->next, &priv->maps);
 
 done:
-        priv->used += add->count;
         gntdev_print_maps(priv, "[new]", add->index);
 }
 
@@ -200,7 +194,7 @@ static int gntdev_del_map(struct grant_map *map)
                 if (map->unmap_ops[i].handle)
                         return -EBUSY;
 
-        map->priv->used -= map->count;
+        atomic_sub(map->count, &pages_mapped);
         list_del(&map->next);
         return 0;
 }
@@ -386,7 +380,6 @@ static int gntdev_open(struct inode *inode, struct file *flip)
 
         INIT_LIST_HEAD(&priv->maps);
         spin_lock_init(&priv->lock);
-        priv->limit = limit;
 
         priv->mm = get_task_mm(current);
         if (!priv->mm) {
@@ -443,19 +436,24 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,
         pr_debug("priv %p, add %d\n", priv, op.count);
         if (unlikely(op.count <= 0))
                 return -EINVAL;
-        if (unlikely(op.count > priv->limit))
-                return -EINVAL;
 
         err = -ENOMEM;
         map = gntdev_alloc_map(priv, op.count);
         if (!map)
                 return err;
+
         if (copy_from_user(map->grants, &u->refs,
                            sizeof(map->grants[0]) * op.count) != 0) {
                 gntdev_free_map(map);
                 return err;
         }
 
+        if (unlikely(atomic_add_return(op.count, &pages_mapped) > limit)) {
+                pr_debug("can't map: over limit\n");
+                gntdev_free_map(map);
+                return err;
+        }
+
         spin_lock(&priv->lock);
         gntdev_add_map(priv, map);
         op.index = map->index << PAGE_SHIFT;
@@ -518,23 +516,6 @@ static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
         return 0;
 }
 
-static long gntdev_ioctl_set_max_grants(struct gntdev_priv *priv,
-                                        struct ioctl_gntdev_set_max_grants __user *u)
-{
-        struct ioctl_gntdev_set_max_grants op;
-
-        if (copy_from_user(&op, u, sizeof(op)) != 0)
-                return -EFAULT;
-        pr_debug("priv %p, limit %d\n", priv, op.count);
-        if (op.count > limit)
-                return -E2BIG;
-
-        spin_lock(&priv->lock);
-        priv->limit = op.count;
-        spin_unlock(&priv->lock);
-        return 0;
-}
-
 static long gntdev_ioctl(struct file *flip,
                          unsigned int cmd, unsigned long arg)
 {
@@ -551,9 +532,6 @@ static long gntdev_ioctl(struct file *flip,
         case IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR:
                 return gntdev_ioctl_get_offset_for_vaddr(priv, ptr);
 
-        case IOCTL_GNTDEV_SET_MAX_GRANTS:
-                return gntdev_ioctl_set_max_grants(priv, ptr);
-
         default:
                 pr_debug("priv %p, unknown cmd %x\n", priv, cmd);
                 return -ENOIOCTLCMD;