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Subject[PATCH v3 14/25] drm: virtio: fix common struct sg_table related issues
Date
The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
numer of the created entries in the DMA address space. However the
subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
called with the original number of the entries passed to dma_map_sg. The
sg_table->nents in turn holds the result of the dma_map_sg call as stated
in include/linux/scatterlist.h. A common mistake was to ignore a result
of the dma_map_sg function and don't use the sg_table->orig_nents at all.

To avoid such issues, lets use common dma-mapping wrappers operating
directly on the struct sg_table objects and adjust references to the
nents and orig_nents respectively.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187
---
drivers/gpu/drm/virtio/virtgpu_object.c | 17 ++++++++---------
drivers/gpu/drm/virtio/virtgpu_vq.c | 10 ++++------
2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
index 6ccbd01..5fe153c 100644
--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -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);
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);
+ 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),
diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 9e663a5..c329147 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -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));
--
1.9.1
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