[PATCH v9 20/32] drm: virtio: fix common struct sg_table related issues

Marek Szyprowski
2020-08-26T06:37:46Z

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>
---
drivers/gpu/drm/virtio/virtgpu_object.c | 36 ++++++++++++++-----------
drivers/gpu/drm/virtio/virtgpu_vq.c | 12 ++++-----
2 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
index e83651b7747d..a0559d3ed362 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, 0);
shmem->mapped = 0;
}

@@ -158,13 +157,13 @@ 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),
@@ -174,13 +173,20 @@ 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));
- (*ents)[si].length = cpu_to_le32(sg->length);
- (*ents)[si].padding = 0;
+ 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;
}

diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 53af60d484a4..7947b1047bd0 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -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));
--
2.17.1