Re: [PATCH v15 5/7] virtio-balloon: Pull page poisoning config out of free page hinting

[Michael S. Tsirkin]

On Thu, Dec 05, 2019 at 08:22:47AM -0800, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> 
> 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 free page reporting. As such pull it out and make it a separate
> bit of config in the probe function.
> 
> In addition we need to add support for the more recent init_on_free feature
> which expects a behavior similar to page poisoning in that we expect the
> page to be pre-zeroed.
> 
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

> ---
>  drivers/virtio/virtio_balloon.c |   23 +++++++++++++++++------
>  1 file changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 15b7f1d8c334..252591bc7e01 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -849,7 +849,6 @@ 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) {
> @@ -916,11 +915,20 @@ 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)) {
> +	}
> +	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
> +		/* Start with poison val of 0 representing general init */
> +		__u32 poison_val = 0;
> +
> +		/*
> +		 * Let the hypervisor know that we are expecting a
> +		 * specific value to be written back in balloon pages.
> +		 */
> +		if (!want_init_on_free())
>  			memset(&poison_val, PAGE_POISON, sizeof(poison_val));
> -			virtio_cwrite(vb->vdev, struct virtio_balloon_config,
> -				      poison_val, &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
> @@ -1021,7 +1029,10 @@ 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 (!want_init_on_free() &&
> +	    (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);