Re: [PATCH v22 3/3] virtio-balloon: don't report free pages when page poisoning is enabled

[Michael S. Tsirkin]

On Wed, Jan 17, 2018 at 01:10:12PM +0800, Wei Wang wrote:
> The guest free pages should not be discarded by the live migration thread
> when page poisoning is enabled with PAGE_POISONING_NO_SANITY=n, because
> skipping the transfer of such poisoned free pages will trigger false
> positive when new pages are allocated and checked on the destination.
> This patch adds a config field, poison_val. Guest writes to the config
> field to tell the host about the poisoning value. The value will be 0 in
> the following cases:
> 1) PAGE_POISONING_NO_SANITY is enabled;
> 2) page poisoning is disabled; or
> 3) PAGE_POISONING_ZERO is enabled.
> 
> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
> Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>


Pls squash with the previous patch. It's not nice to break a
config, then fix it up later.

> ---
>  drivers/virtio/virtio_balloon.c     | 8 ++++++++
>  include/uapi/linux/virtio_balloon.h | 2 ++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index b9561a5..5a42235 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -706,6 +706,7 @@ static struct file_system_type balloon_fs = {
>  static int virtballoon_probe(struct virtio_device *vdev)
>  {
>  	struct virtio_balloon *vb;
> +	__u32 poison_val;
>  	int err;
>  
>  	if (!vdev->config->get) {
> @@ -740,6 +741,13 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  					WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
>  		INIT_WORK(&vb->report_free_page_work, report_free_page_func);
>  		vb->stop_cmd_id = VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID;
> +		if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||
> +		    !page_poisoning_enabled())
> +			poison_val = 0;
> +		else
> +			poison_val = PAGE_POISON;
> +		virtio_cwrite(vb->vdev, struct virtio_balloon_config,
> +			      poison_val, &poison_val);
>  	}
>  
>  	vb->nb.notifier_call = virtballoon_oom_notify;
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index 55e2456..5861876 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -47,6 +47,8 @@ struct virtio_balloon_config {
>  	__u32 actual;
>  	/* Free page report command id, readonly by guest */
>  	__u32 free_page_report_cmd_id;
> +	/* Stores PAGE_POISON if page poisoning with sanity check is in use */
> +	__u32 poison_val;
>  };
>  
>  #define VIRTIO_BALLOON_S_SWAP_IN  0   /* Amount of memory swapped in */
> -- 
> 2.7.4