[PATCH v2 -mm 3/6] block: blk_rq_map_kern uses the bounce buffers for stack buffers

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blk_rq_map_kern is used for kernel internal I/Os. Some callers use
this function with stack buffers but DMA to/from the stack buffers
leads to memory corruption on a non-coherent platform.

This patch make blk_rq_map_kern uses the bounce buffers if a caller
passes a stack buffer (on the all platforms for simplicity).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
---
 block/blk-map.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/block/blk-map.c b/block/blk-map.c
index 0b1af5a..6b0142b 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -268,6 +268,7 @@ int blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf,
 	int reading = rq_data_dir(rq) == READ;
 	int do_copy = 0;
 	struct bio *bio;
+	unsigned long stack_mask = ~(THREAD_SIZE - 1);
 
 	if (len > (q->max_hw_sectors << 9))
 		return -EINVAL;
@@ -278,6 +279,10 @@ int blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf,
 	alignment = queue_dma_alignment(q) | q->dma_pad_mask;
 	do_copy = ((kaddr & alignment) || (len & alignment));
 
+	if (!((kaddr & stack_mask) ^
+	      ((unsigned long)current->stack & stack_mask)))
+		do_copy = 1;
+
 	if (do_copy)
 		bio = bio_copy_kern(q, kbuf, len, gfp_mask, reading);
 	else
-- 
1.5.4.2

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