drm/i915: No longer allow exporting userptr through dma-buf

It doesn't make sense to export a memory address, we will prevent
allowing access this way to different address spaces when we
rework userptr handling, so best to explicitly disable it.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-13-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_userptr.c

@@ -694,10 +694,9 @@ i915_gem_userptr_release(struct drm_i915_gem_object *obj)
 static int
 i915_gem_userptr_dmabuf_export(struct drm_i915_gem_object *obj)
 {
-	if (obj->userptr.mmu_object)
-		return 0;
+	drm_dbg(obj->base.dev, "Exporting userptr no longer allowed\n");
 
-	return i915_gem_userptr_init__mmu_notifier(obj, 0);
+	return -EINVAL;
 }
 
 static int