vhost: Fix vhost_copy_to_user()

vhost: Fix vhost_copy_to_user()

[ Upstream commit 7ced6c98c7ab7a1f6743931e28671b833af79b1e ]

vhost_copy_to_user is used to copy vring used elements to userspace.
We should use VHOST_ADDR_USED instead of VHOST_ADDR_DESC.

Fixes: f88949138058 ("vhost: introduce O(1) vq metadata cache")
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>