diff mbox series

[v7,5/6] virtio-balloon: Pull page poisoning config out of free page hinting

Message ID 20190904151055.13848.27351.stgit@localhost.localdomain (mailing list archive)
State New, archived
Headers show
Series mm / virtio: Provide support for unused page reporting | expand

Commit Message

Alexander Duyck Sept. 4, 2019, 3:10 p.m. UTC 
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 |   19 +++++++++++++------
 mm/page_reporting.c             |    4 ++++
 2 files changed, 17 insertions(+), 6 deletions(-)

Comments

Michael S. Tsirkin Sept. 4, 2019, 7:28 p.m. UTC | #1 
On Wed, Sep 04, 2019 at 08:10:55AM -0700, 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 |   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 */
Alexander Duyck Sept. 4, 2019, 8:32 p.m. UTC | #2 
On Wed, 2019-09-04 at 15:28 -0400, Michael S. Tsirkin wrote:
> On Wed, Sep 04, 2019 at 08:10:55AM -0700, 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 |   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.

I thought it better to err on the side of more information rather than
less. With this the host knows that page poisoning is enabled, but that 0
is an acceptable value.

> 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.

That makes sense.

> 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.

Yeah, I will move that for v8. I will just add an IS_ENABLED check to the
!page_poisoning_enabled check in virtballoon_validate and can drop the
#ifdef check.

Thanks.

- Alex
diff mbox series

Patch

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
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 */