| Message ID | 20200826063316.23486-31-m.szyprowski@samsung.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v9,01/32] drm: prime: add common helper to check scatterlist contiguity | expand |
On 2020-08-26 07:33, Marek Szyprowski wrote: > 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. Reviewed-by: Robin Murphy <robin.murphy@arm.com> > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> > --- > samples/vfio-mdev/mbochs.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > 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); > } >
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); }
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> --- samples/vfio-mdev/mbochs.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)