Commit 75ef337b authored by Marek Szyprowski's avatar Marek Szyprowski
Browse files

drm: virtio: fix common struct sg_table related issues 



The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

Signed-off-by: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
Acked-by: default avatarGerd Hoffmann <kraxel@redhat.com>
parent e96418da

drivers/gpu/drm/virtio/virtgpu_object.c

+21 −15
Original line number Diff line number Diff line
@@ -72,9 +72,8 @@ void virtio_gpu_cleanup_object(struct virtio_gpu_object *bo) 


		if (shmem->pages) {

			if (shmem->mapped) {

				dma_unmap_sg(vgdev->vdev->dev.parent,

					     shmem->pages->sgl, shmem->mapped,

					     DMA_TO_DEVICE);

				dma_unmap_sgtable(vgdev->vdev->dev.parent,

					     shmem->pages, DMA_TO_DEVICE, 0);

				shmem->mapped = 0;

			}
@@ -157,13 +156,13 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev, 
	}



	if (use_dma_api) {

		shmem->mapped = dma_map_sg(vgdev->vdev->dev.parent,

					   shmem->pages->sgl,

					   shmem->pages->nents,

					   DMA_TO_DEVICE);

		*nents = shmem->mapped;

		ret = dma_map_sgtable(vgdev->vdev->dev.parent,

				      shmem->pages, DMA_TO_DEVICE, 0);

		if (ret)

			return ret;

		*nents = shmem->mapped = shmem->pages->nents;

	} else {

		*nents = shmem->pages->nents;

		*nents = shmem->pages->orig_nents;

	}



	*ents = kmalloc_array(*nents, sizeof(struct virtio_gpu_mem_entry),
@@ -173,13 +172,20 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev, 
		return -ENOMEM;

	}



	for_each_sg(shmem->pages->sgl, sg, *nents, si) {

		(*ents)[si].addr = cpu_to_le64(use_dma_api

					       ? sg_dma_address(sg)

					       : sg_phys(sg));

	if (use_dma_api) {

		for_each_sgtable_dma_sg(shmem->pages, sg, si) {

			(*ents)[si].addr = cpu_to_le64(sg_dma_address(sg));

			(*ents)[si].length = cpu_to_le32(sg_dma_len(sg));

			(*ents)[si].padding = 0;

		}

	} else {

		for_each_sgtable_sg(shmem->pages, sg, si) {

			(*ents)[si].addr = cpu_to_le64(sg_phys(sg));

			(*ents)[si].length = cpu_to_le32(sg->length);

			(*ents)[si].padding = 0;

		}

	}



	return 0;

}

drivers/gpu/drm/virtio/virtgpu_vq.c

+5 −7
Original line number Diff line number Diff line
@@ -302,7 +302,7 @@ static struct sg_table *vmalloc_to_sgt(char *data, uint32_t size, int *sg_ents) 
		return NULL;

	}



	for_each_sg(sgt->sgl, sg, *sg_ents, i) {

	for_each_sgtable_sg(sgt, sg, i) {

		pg = vmalloc_to_page(data);

		if (!pg) {

			sg_free_table(sgt);
@@ -603,9 +603,8 @@ void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev, 
	struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);



	if (use_dma_api)

		dma_sync_sg_for_device(vgdev->vdev->dev.parent,

				       shmem->pages->sgl, shmem->pages->nents,

				       DMA_TO_DEVICE);

		dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,

					    shmem->pages, DMA_TO_DEVICE);



	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));

	memset(cmd_p, 0, sizeof(*cmd_p));
@@ -1019,9 +1018,8 @@ void virtio_gpu_cmd_transfer_to_host_3d(struct virtio_gpu_device *vgdev, 
	struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);



	if (use_dma_api)

		dma_sync_sg_for_device(vgdev->vdev->dev.parent,

				       shmem->pages->sgl, shmem->pages->nents,

				       DMA_TO_DEVICE);

		dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,

					    shmem->pages, DMA_TO_DEVICE);



	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));

	memset(cmd_p, 0, sizeof(*cmd_p));