Subject: Re: [PATCH v10 5/6] virtio-balloon: Pull page poisoning config out of free page hinting

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 18 Sep 2019 13:58:55 -0400

On Wed, Sep 18, 2019 at 10:53:05AM -0700, Alexander Duyck wrote:
> From: Alexander Duyck <[email-masked]>
> 
> Currently the page poisoning setting wasn't being enabled unless free page
> hinting was enabled. However we will need the page poisoning tracking logic
> as well for unused page reporting. As such pull it out and make it a
> separate bit of config in the probe function.
> 
> In addition we can actually wrap the code in a check for NO_SANITY. If we
> don't care what is actually in the page we can just default to 0 and leave
> it there.
> 
> Reviewed-by: David Hildenbrand <[email-masked]>
> Signed-off-by: Alexander Duyck <[email-masked]>

I think this one can go in directly. Do you want me to merge it now?

> ---
>  drivers/virtio/virtio_balloon.c |   22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 226fbb995fb0..501a8d0ebf86 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -842,7 +842,6 @@ static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
>  static int virtballoon_probe(struct virtio_device *vdev)
>  {
>  	struct virtio_balloon *vb;
> -	__u32 poison_val;
>  	int err;
>  
>  	if (!vdev->config->get) {
> @@ -909,11 +908,18 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  						  VIRTIO_BALLOON_CMD_ID_STOP);
>  		spin_lock_init(&vb->free_page_list_lock);
>  		INIT_LIST_HEAD(&vb->free_page_list);
> -		if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
> -			memset(&poison_val, PAGE_POISON, sizeof(poison_val));
> -			virtio_cwrite(vb->vdev, struct virtio_balloon_config,
> -				      poison_val, &poison_val);
> -		}
> +	}
> +	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
> +		__u32 poison_val;
> +
> +		/*
> +		 * Let the hypervisor know that we are expecting a
> +		 * specific value to be written back in unused pages.
> +		 */
> +		memset(&poison_val, PAGE_POISON, sizeof(poison_val));
> +
> +		virtio_cwrite(vb->vdev, struct virtio_balloon_config,
> +			      poison_val, &poison_val);
>  	}
>  	/*
>  	 * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
> @@ -1014,7 +1020,9 @@ static int virtballoon_restore(struct virtio_device *vdev)
>  
>  static int virtballoon_validate(struct virtio_device *vdev)
>  {
> -	if (!page_poisoning_enabled())
> +	/* Tell the host whether we care about poisoned pages. */
> +	if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||
> +	    !page_poisoning_enabled())
>  		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
>  
>  	__virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);

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