Re: [PATCH] vfio/mtty: Enforce available_instances

[Kirti Wankhede]

On 6/26/2021 2:56 AM, Alex Williamson wrote:
> The sample mtty mdev driver doesn't actually enforce the number of
> device instances it claims are available.  Implement this properly.
>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
>
> Applies to vfio next branch + Jason's atomic conversion


Does this need to be on top of Jason's patch?
Patch to use mdev_used_ports is reverted here, can it be changed from 
mdev_devices_list to mdev_avail_ports atomic variable?

Change here to use atomic variable looks good to me.

Reviewed by: Kirti Wankhede <kwankhede@xxxxxxxxxx>



>   samples/vfio-mdev/mtty.c |   22 ++++++++++++++++------
>   1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> index ffbaf07a17ea..8b26fecc4afe 100644
> --- a/samples/vfio-mdev/mtty.c
> +++ b/samples/vfio-mdev/mtty.c
> @@ -144,7 +144,7 @@ struct mdev_state {
>   	int nr_ports;
>   };
>   
> -static atomic_t mdev_used_ports;
> +static atomic_t mdev_avail_ports = ATOMIC_INIT(MAX_MTTYS);
>   
>   static const struct file_operations vd_fops = {
>   	.owner          = THIS_MODULE,
> @@ -707,11 +707,20 @@ static int mtty_probe(struct mdev_device *mdev)
>   {
>   	struct mdev_state *mdev_state;
>   	int nr_ports = mdev_get_type_group_id(mdev) + 1;
> +	int avail_ports = atomic_read(&mdev_avail_ports);
>   	int ret;
>   
> +	do {
> +		if (avail_ports < nr_ports)
> +			return -ENOSPC;
> +	} while (!atomic_try_cmpxchg(&mdev_avail_ports,
> +				     &avail_ports, avail_ports - nr_ports));
> +
>   	mdev_state = kzalloc(sizeof(struct mdev_state), GFP_KERNEL);
> -	if (mdev_state == NULL)
> +	if (mdev_state == NULL) {
> +		atomic_add(nr_ports, &mdev_avail_ports);
>   		return -ENOMEM;
> +	}
>   
>   	vfio_init_group_dev(&mdev_state->vdev, &mdev->dev, &mtty_dev_ops);
>   
> @@ -724,6 +733,7 @@ static int mtty_probe(struct mdev_device *mdev)
>   
>   	if (mdev_state->vconfig == NULL) {
>   		kfree(mdev_state);
> +		atomic_add(nr_ports, &mdev_avail_ports);
>   		return -ENOMEM;
>   	}
>   
> @@ -735,9 +745,9 @@ static int mtty_probe(struct mdev_device *mdev)
>   	ret = vfio_register_group_dev(&mdev_state->vdev);
>   	if (ret) {
>   		kfree(mdev_state);
> +		atomic_add(nr_ports, &mdev_avail_ports);
>   		return ret;
>   	}
> -	atomic_add(mdev_state->nr_ports, &mdev_used_ports);
>   
>   	dev_set_drvdata(&mdev->dev, mdev_state);
>   	return 0;
> @@ -746,12 +756,13 @@ static int mtty_probe(struct mdev_device *mdev)
>   static void mtty_remove(struct mdev_device *mdev)
>   {
>   	struct mdev_state *mdev_state = dev_get_drvdata(&mdev->dev);
> +	int nr_ports = mdev_state->nr_ports;
>   
> -	atomic_sub(mdev_state->nr_ports, &mdev_used_ports);
>   	vfio_unregister_group_dev(&mdev_state->vdev);
>   
>   	kfree(mdev_state->vconfig);
>   	kfree(mdev_state);
> +	atomic_add(nr_ports, &mdev_avail_ports);
>   }
>   
>   static int mtty_reset(struct mdev_state *mdev_state)
> @@ -1271,8 +1282,7 @@ static ssize_t available_instances_show(struct mdev_type *mtype,
>   {
>   	unsigned int ports = mtype_get_type_group_id(mtype) + 1;
>   
> -	return sprintf(buf, "%d\n",
> -		       (MAX_MTTYS - atomic_read(&mdev_used_ports)) / ports);
> +	return sprintf(buf, "%d\n", atomic_read(&mdev_avail_ports) / ports);
>   }
>   
>   static MDEV_TYPE_ATTR_RO(available_instances);