linux-kernel - [PATCH AUTOSEL 5.8 039/132] misc: fastrpc: fix common struct sg

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Date:   Mon, 26 Oct 2020 19:50:31 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.8 039/132] misc: fastrpc: fix common struct sg_table related issues

From: Marek Szyprowski <m.szyprowski@...sung.com>

[ Upstream commit 7cd7edb89437457ec36ffdbb970cc314d00c4aba ]

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@...sung.com>
Link: https://lore.kernel.org/r/20200826063316.23486-29-m.szyprowski@samsung.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/misc/fastrpc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 7939c55daceb2..9d68677493163 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -518,7 +518,7 @@ fastrpc_map_dma_buf(struct dma_buf_attachment *attachment,

 	table = &a->sgt;

-	if (!dma_map_sg(attachment->dev, table->sgl, table->nents, dir))
+	if (!dma_map_sgtable(attachment->dev, table, dir, 0))
 		return ERR_PTR(-ENOMEM);

 	return table;
@@ -528,7 +528,7 @@ static void fastrpc_unmap_dma_buf(struct dma_buf_attachment *attach,
 				  struct sg_table *table,
 				  enum dma_data_direction dir)
 {
-	dma_unmap_sg(attach->dev, table->sgl, table->nents, dir);
+	dma_unmap_sgtable(attach->dev, table, dir, 0);
 }

 static void fastrpc_release(struct dma_buf *dmabuf)
-- 
2.25.1