Re: [Xen-devel] [PATCH 2/6] xen-gntdev: Change page limit to be global instead of per-open

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 12/14/2010 06:55 AM, Daniel De Graaf wrote:
> 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.

Does anyone use this ioctl?  Wouldn't it be safer to replace it with a
no-op version?

    J

> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> ---
>  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 c582804..62639af 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -44,13 +44,12 @@ 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;
> @@ -76,8 +75,8 @@ 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,
> @@ -104,9 +103,6 @@ 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:
> @@ -131,7 +127,6 @@ 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);
>  }
> @@ -178,7 +173,7 @@ 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;
>  }
> @@ -360,7 +355,6 @@ 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) {
> @@ -416,19 +410,26 @@ 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;
> @@ -495,24 +496,6 @@ 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)
>  {
> @@ -529,9 +512,6 @@ 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",


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