Re: [PATCH] virtio-balloon: do not attempt to release more than available pages

[Rusty Russell <rusty@rustcorp.com.au>]

On Tuesday 11 March 2008 11:52:46 Anthony Liguori wrote:
> Rusty Russell wrote:
> > 2) Handle the case where we get nonsense from the host, which causes us
> > to wrap around.
>
> Here's my neither compiled nor tested version which should fix this
> problem without breaking the ABI.

Hmm, we could just refuse to grab >= 2G pages.  It is not only reasonable, but
also gives us an opportunity to make another Sophie Blanchard reference![1]

Patch below.

Cheers,
Rusty.
[1] Wow, I actually learned something from a Wikipedia Featured Article.

virtio: handle > 2 billion page balloon targets

If the host asks for a huge target towards_target() can overflow, and
we up oops as we try to release more pages than we have.  The simple
fix is to use a 64-bit value.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r fd0c80dbbd95 drivers/virtio/virtio_balloon.c
--- a/drivers/virtio/virtio_balloon.c	Tue Mar 11 09:21:00 2008 +1100
+++ b/drivers/virtio/virtio_balloon.c	Tue Mar 11 11:25:52 2008 +1100
@@ -152,7 +152,7 @@ static void virtballoon_changed(struct v
 	wake_up(&vb->config_change);
 }
 
-static inline int towards_target(struct virtio_balloon *vb)
+static inline s64 towards_target(struct virtio_balloon *vb)
 {
 	u32 v;
 	__virtio_config_val(vb->vdev,
@@ -176,7 +183,7 @@ static int balloon(void *_vballoon)
 
 	set_freezable();
 	while (!kthread_should_stop()) {
-		int diff;
+		s64 diff;
 
 		try_to_freeze();
 		wait_event_interruptible(vb->config_change,

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