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Subject[PATCH 2/3] 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 <>
drivers/virtio/virtio_balloon.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 6c07793..553cc1f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -238,11 +238,14 @@ static void virtballoon_changed(struct virtio_device *vdev)

static inline s64 towards_target(struct virtio_balloon *vb)
- u32 v;
+ __le32 v;
+ s64 target;
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)

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