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Subject: Re: [PATCH v9 7/8] virtio-balloon: Pull page poisoning config out of
 free page hinting
To:     Alexander Duyck <alexander.duyck@gmail.com>,
        virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org,
        mst@redhat.com, catalin.marinas@arm.com, dave.hansen@intel.com,
        linux-kernel@vger.kernel.org, willy@infradead.org,
        mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org,
        will@kernel.org, linux-arm-kernel@lists.infradead.org,
        osalvador@suse.de
Cc:     yang.zhang.wz@gmail.com, pagupta@redhat.com,
        konrad.wilk@oracle.com, nitesh@redhat.com, riel@surriel.com,
        lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com,
        ying.huang@intel.com, pbonzini@redhat.com,
        dan.j.williams@intel.com, fengguang.wu@intel.com,
        alexander.h.duyck@linux.intel.com, kirill.shutemov@linux.intel.com
References: <20190907172225.10910.34302.stgit@localhost.localdomain>
 <20190907172601.10910.95355.stgit@localhost.localdomain>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <4dfcf372-97be-65ab-1349-75f24aa4f98a@redhat.com>
Date:   Mon, 9 Sep 2019 10:59:08 +0200
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On 07.09.19 19:26, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 
> 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.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> ---
>  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..d2547df7de93 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 hypervisor know that we are expecting a specific
> +		 * value to be written back in unused pages.
> +		 */

"Let the hypervisor know" ... ?

> +		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())
> +	/* Notify host if we care about poison value */

"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);
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David / dhildenb