iommufd/iova_bitmap: Check iova_bitmap_done() after set ahead

After iova_bitmap_set_ahead() returns it may be at the end of the range.
Move iova_bitmap_set_ahead() earlier to avoid unnecessary attempt in
trying to pin the next pages by reusing iova_bitmap_done() check.

Fixes: 2780025 ("iommufd/iova_bitmap: Handle recording beyond the mapped pages")
Link: https://lore.kernel.org/r/20240627110105.62325-7-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Matt Ochs <mochs@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: jpemartins

drivers/iommu/iommufd/iova_bitmap.c

@@ -384,8 +384,6 @@ static int iova_bitmap_advance(struct iova_bitmap *bitmap)
 	bitmap->mapped_base_index += count;
 
 	iova_bitmap_put(bitmap);
-	if (iova_bitmap_done(bitmap))
-		return 0;
 
 	/* Iterate, set and skip any bits requested for next iteration */
 	if (bitmap->set_ahead_length) {
@@ -396,6 +394,9 @@ static int iova_bitmap_advance(struct iova_bitmap *bitmap)
 			return ret;
 	}
 
+	if (iova_bitmap_done(bitmap))
+		return 0;
+
 	/* When advancing the index we pin the next set of bitmap pages */
 	return iova_bitmap_get(bitmap);
 }