From: Marek Szyprowski <m.szyprowski@samsung.com>
To: dri-devel@lists.freedesktop.org,
iommu@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org,
linux-kernel@vger.kernel.org
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
Christoph Hellwig <hch@lst.de>,
Robin Murphy <robin.murphy@arm.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
linux-arm-kernel@lists.infradead.org,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Kirti Wankhede <kwankhede@nvidia.com>,
kvm@vger.kernel.org
Subject: [PATCH v5 36/38] samples: vfio-mdev/mbochs: fix common struct sg_table related issues
Date: Wed, 13 May 2020 15:32:43 +0200 [thread overview]
Message-ID: <20200513133245.6408-36-m.szyprowski@samsung.com> (raw)
In-Reply-To: <20200513133245.6408-1-m.szyprowski@samsung.com>
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>
---
For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/linux-iommu/20200513132114.6046-1-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..e030689 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);
}
--
1.9.1
parent reply other threads:[~2020-05-13 13:34 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <CGME20200513133323eucas1p1519f5901d2a4ee85b781fcc36e9601f7@eucas1p1.samsung.com>]
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