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

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

On 12/14/2010 04:12 PM, Jeremy Fitzhardinge wrote:
> 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
> 

I do not know of any users. If it's preferred to replace with a noop ioctl
instead of the current -ENOSYS return, that's easy to do.

>> 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 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",
>