On Fri, Jul 10, 2020 at 4:31 AM Michael S. Tsirkin mst@redhat.com wrote:
Page reporting features were never supported by legacy hypervisors. Supporting them poses a problem: should we use native endian-ness (like current code assumes)? Or little endian-ness like the virtio spec says? Rather than try to figure out, and since results of incorrect endian-ness are dire, let's just block this configuration.
Cc: stable@vger.kernel.org Signed-off-by: Michael S. Tsirkin mst@redhat.com
So I am not sure about the patch description. In the case of page poison and free page reporting I don't think we are defining anything that doesn't already have a definition of how to use in legacy. Specifically the virtio_balloon_config is already defined as having all fields as little endian in legacy mode, and there is a definition for all of the fields in a virtqueue and how they behave in legacy mode.
As far as I can see the only item that may be an issue is the command ID being supplied via the virtqueue for free page hinting, which appears to be in native endian-ness. Otherwise it would have fallen into the same category since it is making use of virtio_balloon_config and a virtqueue for supplying the page location and length.
drivers/virtio/virtio_balloon.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 5d4b891bf84f..b9bc03345157 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -1107,6 +1107,15 @@ static int virtballoon_restore(struct virtio_device *vdev)
static int virtballoon_validate(struct virtio_device *vdev) {
/** Legacy devices never specified how modern features should behave.* E.g. which endian-ness to use? Better not to assume anything.*/if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT);__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);} /* * Inform the hypervisor that our pages are poisoned or * initialized. If we cannot do that then we should disable
The patch content itself I am fine with since odds are nobody would expect to use these features with a legacy device.
Acked-by: Alexander Duyck alexander.h.duyck@linux.intel.com