Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

Pull vhost cleanup and virtio bugfix
 "There's a single change here, fixing a vhost bug where vhost
  initialization fails due to used ring alignment check being too
  strict"

* tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost:
  vhost: relax used address alignment
  virtio_ring: document alignment requirements

2 files changed, 14 insertions, 3 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ed71b5347a76..cb807d0ea498 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -713,9 +713,13 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
                         r = -EFAULT;
                         break;
                 }
-                if ((a.avail_user_addr & (sizeof *vq->avail->ring - 1)) ||
-                    (a.used_user_addr & (sizeof *vq->used->ring - 1)) ||
-                    (a.log_guest_addr & (sizeof *vq->used->ring - 1))) {
+
+                /* Make sure it's safe to cast pointers to vring types. */
+                BUILD_BUG_ON(__alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE);
+                BUILD_BUG_ON(__alignof__ *vq->used > VRING_USED_ALIGN_SIZE);
+                if ((a.avail_user_addr & (VRING_AVAIL_ALIGN_SIZE - 1)) ||
+                    (a.used_user_addr & (VRING_USED_ALIGN_SIZE - 1)) ||
+                    (a.log_guest_addr & (sizeof(u64) - 1))) {
                         r = -EINVAL;
                         break;
                 }
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index 61c818a7fe70..a3318f31e8e7 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -101,6 +101,13 @@ struct vring {
         struct vring_used *used;
 };
 
+/* Alignment requirements for vring elements.
+ * When using pre-virtio 1.0 layout, these fall out naturally.
+ */
+#define VRING_AVAIL_ALIGN_SIZE 2
+#define VRING_USED_ALIGN_SIZE 4
+#define VRING_DESC_ALIGN_SIZE 16
+
 /* The standard layout for the ring is a continuous chunk of memory which looks
  * like this.  We assume num is a power of 2.
  *