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drm: virtio: fix common struct sg_table related issues

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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: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Marek Szyprowski
2020-04-28 13:10:19 +02:00
parent e96418da0a
commit 75ef337bdb
2 changed files with 26 additions and 22 deletions
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12
drivers/gpu/drm/virtio/virtgpu_vq.c
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@@ -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));