On Wed, Sep 04, 2019 at 08:10:55AM -0700, 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 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@xxxxxxxxxxxxxxx>
> ---
> drivers/virtio/virtio_balloon.c | 19 +++++++++++++------
> mm/page_reporting.c | 4 ++++
> 2 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 226fbb995fb0..2c19457ab573 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 +908,19 @@ 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 = 0;
> +
> +#if !defined(CONFIG_PAGE_POISONING_NO_SANITY)
> + /*
> + * Let hypervisor know that we are expecting a specific
> + * value to be written back in unused pages.
> + */
> + memset(&poison_val, PAGE_POISON, sizeof(poison_val));
> +#endif
> + 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
I'm a bit confused by this part. Should we not just clear
VIRTIO_BALLOON_F_PAGE_POISON completely?
In my mind the value written should be what guest puts in
free pages - and possibly what it expects to find there later.
If it doesn't expect anything there then it makes sense
to clear VIRTIO_BALLOON_F_PAGE_POISON so that host does
not try to put the poison value there.
But I think that it does not make sense to lie to host about the poison
value - I think that if we do send poison value to
host it's reasonable for host to expect free pages
have that value - and even possibly to validate that.
So I think that the hack belongs in virtballoon_validate,
near the page_poisoning_enabled check.
> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> index 5006b08d5eec..35c0fe4c4471 100644
> --- a/mm/page_reporting.c
> +++ b/mm/page_reporting.c
> @@ -299,6 +299,10 @@ int page_reporting_startup(struct page_reporting_dev_info *phdev)
> struct zone *zone;
> int err = 0;
>
> + /* No point in enabling this if it cannot handle any pages */
> + if (!phdev->capacity)
> + return -EINVAL;
> +
> mutex_lock(&page_reporting_mutex);
>
> /* nothing to do if already in use */
