virtio_balloon: Fix endian bug

Although virtio config space fields are usually in guest-native endian,
the spec for the virtio balloon device explicitly states that both fields
in its config space are little-endian.

However, the current virtio_balloon driver does not have a suitable endian
swap for the 'num_pages' field, although it does have one for the 'actual'
field.  This patch corrects the bug, adding sparse annotation while we're
at it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 05f0a80818a2..9e95ca602006 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -234,11 +234,14 @@ static void virtballoon_changed(struct virtio_device *vdev)
 
 static inline s64 towards_target(struct virtio_balloon *vb)
 {
-        u32 v;
+        __le32 v;
+        s64 target;
+
         vb->vdev->config->get(vb->vdev,
                               offsetof(struct virtio_balloon_config, num_pages),
                               &v, sizeof(v));
-        return (s64)v - vb->num_pages;
+        target = le32_to_cpu(v);
+        return target - vb->num_pages;
 }
 
 static void update_balloon_size(struct virtio_balloon *vb)