linux-kernel - Re: [PATCH v5] drm/virtio: use virtio_max_dma

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Message-ID: <2e6eba7b-5f46-e9e8-f6b2-3e80e95754e9@redhat.com>
Date:   Thu, 22 Aug 2019 13:33:37 +0200
From:   Laszlo Ersek <lersek@...hat.com>
To:     Gerd Hoffmann <kraxel@...hat.com>, dri-devel@...ts.freedesktop.org
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] drm/virtio: use virtio_max_dma_size

On 08/21/19 13:12, Gerd Hoffmann wrote:
> We must make sure our scatterlist segments are not too big, otherwise
> we might see swiotlb failures (happens with sev, also reproducable with
> swiotlb=force).
> 
> Suggested-by: Laszlo Ersek <lersek@...hat.com>
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_object.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
> index b2da31310d24..09b526518f5a 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
> @@ -204,6 +204,7 @@ int virtio_gpu_object_get_sg_table(struct virtio_gpu_device *qdev,
>  		.interruptible = false,
>  		.no_wait_gpu = false
>  	};
> +	size_t max_segment;
>  
>  	/* wtf swapping */
>  	if (bo->pages)
> @@ -215,8 +216,13 @@ int virtio_gpu_object_get_sg_table(struct virtio_gpu_device *qdev,
>  	if (!bo->pages)
>  		goto out;
>  
> -	ret = sg_alloc_table_from_pages(bo->pages, pages, nr_pages, 0,
> -					nr_pages << PAGE_SHIFT, GFP_KERNEL);
> +	max_segment = virtio_max_dma_size(qdev->vdev);
> +	max_segment &= PAGE_MASK;
> +	if (max_segment > SCATTERLIST_MAX_SEGMENT)
> +		max_segment = SCATTERLIST_MAX_SEGMENT;
> +	ret = __sg_alloc_table_from_pages(bo->pages, pages, nr_pages, 0,
> +					  nr_pages << PAGE_SHIFT,
> +					  max_segment, GFP_KERNEL);
>  	if (ret)
>  		goto out;
>  	return 0;
> 

Reviewed-by: Laszlo Ersek <lersek@...hat.com>

Thanks!
Laszlo