linux-kernel - Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export

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Date: Mon, 25 Mar 2024 15:38:06 -0700
From: Dominik Behr <dbehr@...omium.org>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org, Rob Clark <robdclark@...omium.org>, 
	Dominik Behr <dbehr@...omium.org>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Sumit Semwal <sumit.semwal@...aro.org>, Christian König <christian.koenig@....com>, 
	Simon Ser <contact@...rsion.fr>, open list <linux-kernel@...r.kernel.org>, 
	"open list:DMA BUFFER SHARING FRAMEWORK:Keyword:bdma_(?:buf|fence|resv)b" <linux-media@...r.kernel.org>, 
	"moderated list:DMA BUFFER SHARING FRAMEWORK:Keyword:bdma_(?:buf|fence|resv)b" <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export

It also fixes importing virtgpu blobs into real hardware, for instance
amdgpu for DRI_PRIME rendering.


On Fri, Mar 22, 2024 at 2:48 PM Rob Clark <robdclark@...il.com> wrote:
>
> From: Rob Clark <robdclark@...omium.org>
>
> virtgpu "vram" GEM objects do not implement obj->get_sg_table().  But
> they also don't use drm_gem_map_dma_buf().  In fact they may not even
> have guest visible pages.  But it is perfectly fine to export and share
> with other virtual devices.
>
> Reported-by: Dominik Behr <dbehr@...omium.org>
> Fixes: 207395da5a97 ("drm/prime: reject DMA-BUF attach when get_sg_table is missing")
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/drm_prime.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 7352bde299d5..64dd6276e828 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -582,7 +582,12 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
>  {
>         struct drm_gem_object *obj = dma_buf->priv;
>
> -       if (!obj->funcs->get_sg_table)
> +       /*
> +        * drm_gem_map_dma_buf() requires obj->get_sg_table(), but drivers
> +        * that implement their own ->map_dma_buf() do not.
> +        */
> +       if ((dma_buf->ops->map_dma_buf == drm_gem_map_dma_buf) &&
> +           !obj->funcs->get_sg_table)
>                 return -ENOSYS;
>
>         return drm_gem_pin(obj);
> --
> 2.44.0
>