drm/gem: Fix mmap fake offset handling for drm_gem_object_funcs.mmap

Commit c40069cb7bd6 ("drm: add mmap() to drm_gem_object_funcs")
introduced a GEM object mmap() hook which is expected to subtract the
fake offset from vm_pgoff. However, for mmap() on dmabufs, there is not
a fake offset.

To fix this, let's always call mmap() object callback with an offset of 0,
and leave it up to drm_gem_mmap_obj() to remove the fake offset.

TTM still needs the fake offset, so we have to add it back until that's
fixed.

Fixes: c40069cb7bd6 ("drm: add mmap() to drm_gem_object_funcs")
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191024191859.31700-1-robh@kernel.org

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index f4dd09b71a3f..4b34a278d65b 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -480,6 +480,13 @@ EXPORT_SYMBOL(ttm_bo_mmap);
 int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
 {
 	ttm_bo_get(bo);
+
+	/*
+	 * FIXME: &drm_gem_object_funcs.mmap is called with the fake offset
+	 * removed. Add it back here until the rest of TTM works without it.
+	 */
+	vma->vm_pgoff += drm_vma_node_start(&bo->base.vma_node);
+
 	ttm_bo_mmap_vma_setup(bo, vma);
 	return 0;
 }