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(GMT) Received: from eusmgms2.samsung.com (unknown [182.198.249.180]) by eusmtrp1.samsung.com (KnoxPortal) with ESMTP id 20200512090129eusmtrp1cc27ec6d1a740863c5c174195c999886~OPF0n7TdP0188101881eusmtrp1f; Tue, 12 May 2020 09:01:29 +0000 (GMT) X-AuditID: cbfec7f2-ef1ff7000001ef66-b4-5eba65e97ca9 Received: from eusmtip1.samsung.com ( [203.254.199.221]) by eusmgms2.samsung.com (EUCPMTA) with SMTP id AC.03.07950.9E56ABE5; Tue, 12 May 2020 10:01:29 +0100 (BST) Received: from AMDC2765.digital.local (unknown [106.120.51.73]) by eusmtip1.samsung.com (KnoxPortal) with ESMTPA id 20200512090128eusmtip14ace71a0d963c54a40acb63ce54fcc29~OPF0Csyzt1181011810eusmtip1w; Tue, 12 May 2020 09:01:28 +0000 (GMT) From: Marek Szyprowski To: dri-devel@lists.freedesktop.org, iommu@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 36/38] samples: vfio-mdev/mbochs: fix common struct sg_table related issues Date: Tue, 12 May 2020 11:00:56 +0200 Message-Id: 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linux-arm-kernel@lists.infradead.org, Marek Szyprowski MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org 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 --- For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents vs. orig_nents misuse' thread: https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsung.com/T/ --- 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 3cc5e59..f2c62e0 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)) 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); sg_free_table(sg); kfree(sg); }