Re: [PATCH] drm/shmem-helper: Reset vma->vm_ops before calling dma_buf_mmap()

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 24 Jul 2023 13:26:10 +0200
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> The dma-buf backend is supposed to provide its own vm_ops, but some
> implementation just have nothing special to do and leave vm_ops
> untouched, probably expecting this field to be zero initialized (this
> is the case with the system_heap implementation for instance).
> Let's reset vma->vm_ops to NULL to keep things working with these
> implementations.
> 
> Fixes: 26d3ac3cb04d ("drm/shmem-helpers: Redirect mmap for imported dma-buf")
> Cc: <stable@vger.kernel.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Reported-by: Roman Stratiienko <roman.stratiienko@globallogic.com>

Adding Roman's tested-by coming from [1]

Tested-by: Roman Stratiienko <r.stratiienko@gmail.com>

[1]https://gitlab.freedesktop.org/mesa/mesa/-/issues/9416#note_2013722

> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 4ea6507a77e5..baaf0e0feb06 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -623,7 +623,13 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
>  	int ret;
>  
>  	if (obj->import_attach) {
> +		/* Reset both vm_ops and vm_private_data, so we don't end up with
> +		 * vm_ops pointing to our implementation if the dma-buf backend
> +		 * doesn't set those fields.
> +		 */
>  		vma->vm_private_data = NULL;
> +		vma->vm_ops = NULL;
> +
>  		ret = dma_buf_mmap(obj->dma_buf, vma, 0);
>  
>  		/* Drop the reference drm_gem_mmap_obj() acquired.*/