Subject: Re: [RFC PATCH 01/24] vhost-vdpa: fix backend feature ioctls

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 24 Sep 2020 03:50:09 -0400

On Thu, Sep 24, 2020 at 11:21:02AM +0800, Jason Wang wrote:
> Commit 653055b9acd4 ("vhost-vdpa: support get/set backend features")
> introduces two malfunction backend features ioctls:
> 
> 1) the ioctls was blindly added to vring ioctl instead of vdpa device
>    ioctl
> 2) vhost_set_backend_features() was called when dev mutex has already
>    been held which will lead a deadlock
> 
> This patch fixes the above issues.
> 
> Cc: Eli Cohen <[email-masked]>
> Reported-by: Zhu Lingshan <[email-masked]>
> Fixes: 653055b9acd4 ("vhost-vdpa: support get/set backend features")
> Signed-off-by: Jason Wang <[email-masked]>

Don't we want the fixes queued right now, as opposed to the rest of the
RFC?

> ---
>  drivers/vhost/vdpa.c | 30 ++++++++++++++++--------------
>  1 file changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 3fab94f88894..796fe979f997 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -353,8 +353,6 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>  	struct vdpa_callback cb;
>  	struct vhost_virtqueue *vq;
>  	struct vhost_vring_state s;
> -	u64 __user *featurep = argp;
> -	u64 features;
>  	u32 idx;
>  	long r;
>  
> @@ -381,18 +379,6 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>  
>  		vq->last_avail_idx = vq_state.avail_index;
>  		break;
> -	case VHOST_GET_BACKEND_FEATURES:
> -		features = VHOST_VDPA_BACKEND_FEATURES;
> -		if (copy_to_user(featurep, &features, sizeof(features)))
> -			return -EFAULT;
> -		return 0;
> -	case VHOST_SET_BACKEND_FEATURES:
> -		if (copy_from_user(&features, featurep, sizeof(features)))
> -			return -EFAULT;
> -		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
> -			return -EOPNOTSUPP;
> -		vhost_set_backend_features(&v->vdev, features);
> -		return 0;
>  	}
>  
>  	r = vhost_vring_ioctl(&v->vdev, cmd, argp);
> @@ -440,8 +426,20 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>  	struct vhost_vdpa *v = filep->private_data;
>  	struct vhost_dev *d = &v->vdev;
>  	void __user *argp = (void __user *)arg;
> +	u64 __user *featurep = argp;
> +	u64 features;
>  	long r;
>  
> +	if (cmd == VHOST_SET_BACKEND_FEATURES) {
> +		r = copy_from_user(&features, featurep, sizeof(features));
> +		if (r)
> +			return r;
> +		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
> +			return -EOPNOTSUPP;
> +		vhost_set_backend_features(&v->vdev, features);
> +		return 0;
> +	}
> +
>  	mutex_lock(&d->mutex);
>  
>  	switch (cmd) {
> @@ -476,6 +474,10 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>  	case VHOST_VDPA_SET_CONFIG_CALL:
>  		r = vhost_vdpa_set_config_call(v, argp);
>  		break;
> +	case VHOST_GET_BACKEND_FEATURES:
> +		features = VHOST_VDPA_BACKEND_FEATURES;
> +		r = copy_to_user(featurep, &features, sizeof(features));
> +		break;
>  	default:
>  		r = vhost_dev_ioctl(&v->vdev, cmd, argp);
>  		if (r == -ENOIOCTLCMD)
> -- 
> 2.20.1