From ca72cc348355fbc969f5fa00fa94d584920d403b Mon Sep 17 00:00:00 2001 From: Alexander Duyck Date: Mon, 13 Jul 2020 13:35:39 -0700 Subject: [PATCH] virtio-balloon: Document byte ordering of poison_val The poison_val field in the virtio_balloon_config is treated as a little-endian field by the host. Since we are currently only having to deal with a single byte poison value this isn't a problem, however if the value should ever expand it would cause byte ordering issues. Document that in the code so that we know that if the value should ever expand we need to byte swap the value on big-endian architectures. Signed-off-by: Alexander Duyck Link: https://lore.kernel.org/r/20200713203539.17140.71425.stgit@localhost.localdomain Signed-off-by: Michael S. Tsirkin Acked-by: David Hildenbrand --- drivers/virtio/virtio_balloon.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 1f157d2f49526..d0fd8f8dc6ed0 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -974,6 +974,11 @@ static int virtballoon_probe(struct virtio_device *vdev) /* * Let the hypervisor know that we are expecting a * specific value to be written back in balloon pages. + * + * If the PAGE_POISON value was larger than a byte we would + * need to byte swap poison_val here to guarantee it is + * little-endian. However for now it is a single byte so we + * can pass it as-is. */ if (!want_init_on_free()) memset(&poison_val, PAGE_POISON, sizeof(poison_val));