netdev - Re: [PATCH V2 9/9] vhost: do not return -EAGIAN for non blocking invalidation too early

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Date:   Wed, 31 Jul 2019 11:59:50 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, jgg@...pe.ca
Subject: Re: [PATCH V2 9/9] vhost: do not return -EAGIAN for non blocking
 invalidation too early

A little typo in the title: s/EAGIAN/EAGAIN

Thanks,
Stefano

On Wed, Jul 31, 2019 at 04:46:55AM -0400, Jason Wang wrote:
> Instead of returning -EAGAIN unconditionally, we'd better do that only
> we're sure the range is overlapped with the metadata area.
> 
> Reported-by: Jason Gunthorpe <jgg@...pe.ca>
> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/vhost/vhost.c | 32 +++++++++++++++++++-------------
>  1 file changed, 19 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index fc2da8a0c671..96c6aeb1871f 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -399,16 +399,19 @@ static void inline vhost_vq_sync_access(struct vhost_virtqueue *vq)
>  	smp_mb();
>  }
>  
> -static void vhost_invalidate_vq_start(struct vhost_virtqueue *vq,
> -				      int index,
> -				      unsigned long start,
> -				      unsigned long end)
> +static int vhost_invalidate_vq_start(struct vhost_virtqueue *vq,
> +				     int index,
> +				     unsigned long start,
> +				     unsigned long end,
> +				     bool blockable)
>  {
>  	struct vhost_uaddr *uaddr = &vq->uaddrs[index];
>  	struct vhost_map *map;
>  
>  	if (!vhost_map_range_overlap(uaddr, start, end))
> -		return;
> +		return 0;
> +	else if (!blockable)
> +		return -EAGAIN;
>  
>  	spin_lock(&vq->mmu_lock);
>  	++vq->invalidate_count;
> @@ -423,6 +426,8 @@ static void vhost_invalidate_vq_start(struct vhost_virtqueue *vq,
>  		vhost_set_map_dirty(vq, map, index);
>  		vhost_map_unprefetch(map);
>  	}
> +
> +	return 0;
>  }
>  
>  static void vhost_invalidate_vq_end(struct vhost_virtqueue *vq,
> @@ -443,18 +448,19 @@ static int vhost_invalidate_range_start(struct mmu_notifier *mn,
>  {
>  	struct vhost_dev *dev = container_of(mn, struct vhost_dev,
>  					     mmu_notifier);
> -	int i, j;
> -
> -	if (!mmu_notifier_range_blockable(range))
> -		return -EAGAIN;
> +	bool blockable = mmu_notifier_range_blockable(range);
> +	int i, j, ret;
>  
>  	for (i = 0; i < dev->nvqs; i++) {
>  		struct vhost_virtqueue *vq = dev->vqs[i];
>  
> -		for (j = 0; j < VHOST_NUM_ADDRS; j++)
> -			vhost_invalidate_vq_start(vq, j,
> -						  range->start,
> -						  range->end);
> +		for (j = 0; j < VHOST_NUM_ADDRS; j++) {
> +			ret = vhost_invalidate_vq_start(vq, j,
> +							range->start,
> +							range->end, blockable);
> +			if (ret)
> +				return ret;
> +		}
>  	}
>  
>  	return 0;
> -- 
> 2.18.1
> 

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