async_xor: dma_map destination DMA_BIDIRECTIONAL

Mapping the destination multiple times is a misuse of the dma-api.
Since the destination may be reused as a source, ensure that it is only
mapped once and that it is mapped bidirectionally.  This appears to add
ugliness on the unmap side in that it always reads back the destination
address from the descriptor, but gcc can determine that dma_unmap is a
nop and not emit the code that calculates its arguments.

Cc: <stable@kernel.org>
Cc: Saeed Bishara <saeed@marvell.com>
Acked-by: Yuri Tikhonov <yur@emcraft.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/crypto/async_tx/async_xor.c b/crypto/async_tx/async_xor.c
index c029d3e..595b786 100644
--- a/crypto/async_tx/async_xor.c
+++ b/crypto/async_tx/async_xor.c
@@ -53,10 +53,17 @@ do_async_xor(struct dma_chan *chan, struct page *dest, struct page **src_list,
 	int xor_src_cnt;
 	dma_addr_t dma_dest;
 
-	dma_dest = dma_map_page(dma->dev, dest, offset, len, DMA_FROM_DEVICE);
-	for (i = 0; i < src_cnt; i++)
+	/* map the dest bidrectional in case it is re-used as a source */
+	dma_dest = dma_map_page(dma->dev, dest, offset, len, DMA_BIDIRECTIONAL);
+	for (i = 0; i < src_cnt; i++) {
+		/* only map the dest once */
+		if (unlikely(src_list[i] == dest)) {
+			dma_src[i] = dma_dest;
+			continue;
+		}
 		dma_src[i] = dma_map_page(dma->dev, src_list[i], offset,
 					  len, DMA_TO_DEVICE);
+	}
 
 	while (src_cnt) {
 		async_flags = flags;