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authorMarek Szyprowski <m.szyprowski@samsung.com>2020-04-30 13:57:22 +0200
committerMarek Szyprowski <m.szyprowski@samsung.com>2020-09-10 08:19:46 +0200
commitbe0704beb229431f206fee3ddd65fa2c5eebdce3 (patch)
treec3a4fcb2e39e3637d5bc5f1a61fb3415475a7c0e /samples
parent62296b395a512930686666089ad285b1f78fd2f0 (diff)
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samples: vfio-mdev/mbochs: 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. While touching this code, also add missing call to dma_unmap_sgtable. Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Diffstat (limited to 'samples')
-rw-r--r--samples/vfio-mdev/mbochs.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
index 3cc5e5921682..e03068917273 100644
--- a/samples/vfio-mdev/mbochs.c
+++ b/samples/vfio-mdev/mbochs.c
@@ -846,7 +846,7 @@ static struct sg_table *mbochs_map_dmabuf(struct dma_buf_attachment *at,
if (sg_alloc_table_from_pages(sg, dmabuf->pages, dmabuf->pagecount,
0, dmabuf->mode.size, GFP_KERNEL) < 0)
goto err2;
- if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
+ if (dma_map_sgtable(at->dev, sg, direction, 0))
goto err3;
return sg;
@@ -868,6 +868,7 @@ static void mbochs_unmap_dmabuf(struct dma_buf_attachment *at,
dev_dbg(dev, "%s: %d\n", __func__, dmabuf->id);
+ dma_unmap_sgtable(at->dev, sg, direction, 0);
sg_free_table(sg);
kfree(sg);
}