drm: Set vm_ops to GEM object's values during mmap

The GEM mmap code relies on the GEM object's mmap callback to set the
VMA's vm_ops field. This is easily forgotten and already led to a memory
leak in the CMA helpers. Instead set the vm_ops field in the DRM core
code to the GEM object's value. Drivers with different needs can override
this in their mmap callback.

v2:
	* support (vm_ops == NULL) if mmap is given; required by VRAM
	  helpers
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: f5ca8eb6 ("drm/cma-helper: Implement mmap as GEM CMA object functions")
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Eric Anholt <eric@anholt.net>
Cc: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210115093038.10345-1-tzimmermann@suse.de

drivers/gpu/drm/drm_gem.c

@@ -1068,20 +1068,17 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
 	drm_gem_object_get(obj);
 
 	vma->vm_private_data = obj;
+	vma->vm_ops = obj->funcs->vm_ops;
 
 	if (obj->funcs->mmap) {
 		ret = obj->funcs->mmap(obj, vma);
-		if (ret) {
-			drm_gem_object_put(obj);
-			return ret;
-		}
+		if (ret)
+			goto err_drm_gem_object_put;
 		WARN_ON(!(vma->vm_flags & VM_DONTEXPAND));
 	} else {
-		if (obj->funcs->vm_ops)
-			vma->vm_ops = obj->funcs->vm_ops;
-		else {
-			drm_gem_object_put(obj);
-			return -EINVAL;
+		if (!vma->vm_ops) {
+			ret = -EINVAL;
+			goto err_drm_gem_object_put;
 		}
 
 		vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
@@ -1090,6 +1087,10 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
 	}
 
 	return 0;
+
+err_drm_gem_object_put:
+	drm_gem_object_put(obj);
+	return ret;
 }
 EXPORT_SYMBOL(drm_gem_mmap_obj);
 

drivers/gpu/drm/drm_prime.c

@@ -717,6 +717,8 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
 	vma->vm_pgoff += drm_vma_node_start(&obj->vma_node);
 
 	if (obj->funcs && obj->funcs->mmap) {
+		vma->vm_ops = obj->funcs->vm_ops;
+
 		ret = obj->funcs->mmap(obj, vma);
 		if (ret)
 			return ret;