[PATCH 2/7] xen-gntdev: Change page limit to be global instead of per-open

[Daniel De Graaf <dgdegra@tycho.nsa.gov>]

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.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
---
 drivers/xen/gntdev.c |   48 ++++++++++++++----------------------------------
 1 files changed, 14 insertions(+), 34 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 387c5f1..7e21592 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -45,13 +45,12 @@ MODULE_DESCRIPTION("User-space granted page access driver");
 
 static int debug = 0;
 module_param(debug, int, 0644);
-static int limit = 1024;
+static int limit = 1024*1024;
 module_param(limit, int, 0644);
+static atomic_t pages_mapped = ATOMIC_INIT(0);
 
 struct gntdev_priv {
 	struct list_head maps;
-	uint32_t used;
-	uint32_t limit;
 	spinlock_t lock;
 	struct mm_struct *mm;
 	struct mmu_notifier mn;
@@ -78,8 +77,8 @@ static void gntdev_print_maps(struct gntdev_priv *priv,
 {
 	struct grant_map *map;
 
-	printk("%s: maps list (priv %p, usage %d/%d)\n",
-	       __FUNCTION__, priv, priv->used, priv->limit);
+	printk("%s: maps list (priv %p)\n",
+	       __FUNCTION__, priv);
 	list_for_each_entry(map, &priv->maps, next)
 		printk("  index %2d, count %2d %s\n",
 		       map->index, map->count,
@@ -115,9 +114,6 @@ 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:
@@ -148,7 +144,6 @@ 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;
 	if (debug)
 		gntdev_print_maps(priv, "[new]", add->index);
 }
@@ -195,7 +190,7 @@ 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 +381,6 @@ 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) {
@@ -442,19 +436,26 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *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))
+	{
+		if (debug)
+			printk("%s: can't map: over limit\n", __FUNCTION__);
+		gntdev_free_map(map);
+		return err;
+	}
+
 	spin_lock(&priv->lock);
 	gntdev_add_map(priv, map);
 	op.index = map->index << PAGE_SHIFT;
@@ -521,24 +522,6 @@ 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;
-	if (debug)
-		printk("%s: priv %p, limit %d\n", __FUNCTION__, priv, op.count);
-	if (op.count > limit)
-		return -EINVAL;
-
-	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)
 {
@@ -555,9 +538,6 @@ 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:
 		if (debug)
 			printk("%s: priv %p, unknown cmd %x\n",
-- 
1.7.2.3