1 files changed, 6 insertions, 2 deletions

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 284ff2436829..513600612995 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -361,10 +361,14 @@ struct vfio_iommu_type1_dma_map {
 #define VFIO_IOMMU_MAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 13)
 
 /**
- * VFIO_IOMMU_UNMAP_DMA - _IOW(VFIO_TYPE, VFIO_BASE + 14, struct vfio_dma_unmap)
+ * VFIO_IOMMU_UNMAP_DMA - _IOWR(VFIO_TYPE, VFIO_BASE + 14,
+ *                                                      struct vfio_dma_unmap)
  *
  * Unmap IO virtual addresses using the provided struct vfio_dma_unmap.
- * Caller sets argsz.
+ * Caller sets argsz.  The actual unmapped size is returned in the size
+ * field.  No guarantee is made to the user that arbitrary unmaps of iova
+ * or size different from those used in the original mapping call will
+ * succeed.
  */
 struct vfio_iommu_type1_dma_unmap {
         __u32   argsz;