Re: [PATCH v2 1/8] drm: Add dummy page per device or GEM object

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 21.06.20 um 08:03 schrieb Andrey Grodzovsky:
> Will be used to reroute CPU mapped BO's page faults once
> device is removed.
>
> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
> ---
>   drivers/gpu/drm/drm_file.c  |  8 ++++++++
>   drivers/gpu/drm/drm_prime.c | 10 ++++++++++
>   include/drm/drm_file.h      |  2 ++
>   include/drm/drm_gem.h       |  2 ++
>   4 files changed, 22 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index c4c704e..67c0770 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -188,6 +188,12 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
>   			goto out_prime_destroy;
>   	}
>   
> +	file->dummy_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
> +	if (!file->dummy_page) {
> +		ret = -ENOMEM;
> +		goto out_prime_destroy;
> +	}
> +
>   	return file;
>   
>   out_prime_destroy:
> @@ -284,6 +290,8 @@ void drm_file_free(struct drm_file *file)
>   	if (dev->driver->postclose)
>   		dev->driver->postclose(dev, file);
>   
> +	__free_page(file->dummy_page);
> +
>   	drm_prime_destroy_file_private(&file->prime);
>   
>   	WARN_ON(!list_empty(&file->event_list));
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 1de2cde..c482e9c 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -335,6 +335,13 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
>   
>   	ret = drm_prime_add_buf_handle(&file_priv->prime,
>   			dma_buf, *handle);
> +
> +	if (!ret) {
> +		obj->dummy_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
> +		if (!obj->dummy_page)
> +			ret = -ENOMEM;
> +	}
> +

While the per file case still looks acceptable this is a clear NAK since 
it will massively increase the memory needed for a prime exported object.

I think that this is quite overkill in the first place and for the hot 
unplug case we can just use the global dummy page as well.

Christian.

>   	mutex_unlock(&file_priv->prime.lock);
>   	if (ret)
>   		goto fail;
> @@ -1006,6 +1013,9 @@ void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg)
>   		dma_buf_unmap_attachment(attach, sg, DMA_BIDIRECTIONAL);
>   	dma_buf = attach->dmabuf;
>   	dma_buf_detach(attach->dmabuf, attach);
> +
> +	__free_page(obj->dummy_page);
> +
>   	/* remove the reference */
>   	dma_buf_put(dma_buf);
>   }
> diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
> index 19df802..349a658 100644
> --- a/include/drm/drm_file.h
> +++ b/include/drm/drm_file.h
> @@ -335,6 +335,8 @@ struct drm_file {
>   	 */
>   	struct drm_prime_file_private prime;
>   
> +	struct page *dummy_page;
> +
>   	/* private: */
>   #if IS_ENABLED(CONFIG_DRM_LEGACY)
>   	unsigned long lock_count; /* DRI1 legacy lock count */
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 0b37506..47460d1 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -310,6 +310,8 @@ struct drm_gem_object {
>   	 *
>   	 */
>   	const struct drm_gem_object_funcs *funcs;
> +
> +	struct page *dummy_page;
>   };
>   
>   /**

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