On Thu, Mar 2, 2023 at 6:35 AM Simon Ser <contact@xxxxxxxxxxx> wrote:
>
> drm_gem_map_dma_buf() requires drm_gem_object_funcs.get_sg_table
> to be implemented, or else WARNs.
>
> Allow drivers to leave this hook unimplemented to implement purely
> local DMA-BUFs (ie, DMA-BUFs which cannot be imported anywhere
> else but the device which allocated them). In that case, reject
> imports to other devices in drm_gem_map_attach().
>
> v2: new patch
>
> Signed-off-by: Simon Ser <contact@xxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Cc: Tian Tao <tiantao6@xxxxxxxxxxxxx>
> Cc: Maxime Ripard <maxime@xxxxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Cc: Hans de Goede <hdegoede@xxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_prime.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index f924b8b4ab6b..ab1d21d63a03 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -544,7 +544,8 @@ int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
> * Optional pinning of buffers is handled at dma-buf attach and detach time in
> * drm_gem_map_attach() and drm_gem_map_detach(). Backing storage itself is
> * handled by drm_gem_map_dma_buf() and drm_gem_unmap_dma_buf(), which relies on
> - * &drm_gem_object_funcs.get_sg_table.
> + * &drm_gem_object_funcs.get_sg_table. If &drm_gem_object_funcs.get_sg_table is
> + * unimplemented, exports into another device are rejected.
> *
> * For kernel-internal access there's drm_gem_dmabuf_vmap() and
> * drm_gem_dmabuf_vunmap(). Userspace mmap support is provided by
> @@ -583,6 +584,9 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
> {
> struct drm_gem_object *obj = dma_buf->priv;
>
> + if (!obj->funcs->get_sg_table)
> + return -EOPNOTSUPP;
This breaks virtgpu, where buffers may not necessarily have guest
backing pages, but still may be shared with other virtual devices
(because the host side buffer _does_ have backing pages)
BR,
-R
> +
> return drm_gem_pin(obj);
> }
> EXPORT_SYMBOL(drm_gem_map_attach);
> --
> 2.39.2
>
>
