drm/vmwgfx: Allow dropped masters render-node like access on legacy nodes v2

Applications like gnome-shell may try to render after dropping master
privileges. Since the driver should now be safe against this scenario,
allow those applications to use their legacy node like a render node.

v2: Add missing return statement.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 5b8595b..3361769 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -911,6 +911,12 @@
 				  "surface reference.\n");
 			return -EACCES;
 		}
+		if (ACCESS_ONCE(vmw_fpriv(file_priv)->locked_master)) {
+			DRM_ERROR("Locked master refused legacy "
+				  "surface reference.\n");
+			return -EACCES;
+		}
+
 		handle = u_handle;
 	}