[PATCH] drm/virtio: use virtio_max_dma_size

[PATCH] drm/virtio: use virtio_max_dma_size

[Gerd Hoffmann]

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).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.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..6e44568813dd 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
 	};
+	unsigned 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 &= ~(size_t)(PAGE_SIZE - 1);
+	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;
-- 
2.18.1

Re: [PATCH] drm/virtio: use virtio_max_dma_size

[Christoph Hellwig]

On Thu, Aug 08, 2019 at 05:34:45PM +0200, 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).

Btw, any chance I could also draft you to replace the remaining
abuses of swiotlb_max_segment and swiotlb_nr_tbl in drm with proper
dma level interface?