1 files changed, 20 insertions, 1 deletions

diff --git a/block/blk-map.c b/block/blk-map.c
index 3c942bd6422a..0b1af5a3537c 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -255,10 +255,18 @@ EXPORT_SYMBOL(blk_rq_unmap_user);
  * @kbuf:       the kernel buffer
  * @len:        length of user data
  * @gfp_mask:   memory allocation flags
+ *
+ * Description:
+ *    Data will be mapped directly if possible. Otherwise a bounce
+ *    buffer is used.
  */
 int blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf,
                     unsigned int len, gfp_t gfp_mask)
 {
+        unsigned long kaddr;
+        unsigned int alignment;
+        int reading = rq_data_dir(rq) == READ;
+        int do_copy = 0;
         struct bio *bio;
 
         if (len > (q->max_hw_sectors << 9))
@@ -266,13 +274,24 @@ int blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf,
         if (!len || !kbuf)
                 return -EINVAL;
 
-        bio = bio_map_kern(q, kbuf, len, gfp_mask);
+        kaddr = (unsigned long)kbuf;
+        alignment = queue_dma_alignment(q) | q->dma_pad_mask;
+        do_copy = ((kaddr & alignment) || (len & alignment));
+
+        if (do_copy)
+                bio = bio_copy_kern(q, kbuf, len, gfp_mask, reading);
+        else
+                bio = bio_map_kern(q, kbuf, len, gfp_mask);
+
         if (IS_ERR(bio))
                 return PTR_ERR(bio);
 
         if (rq_data_dir(rq) == WRITE)
                 bio->bi_rw |= (1 << BIO_RW);
 
+        if (do_copy)
+                rq->cmd_flags |= REQ_COPY_USER;
+
         blk_rq_bio_prep(q, rq, bio);
         blk_queue_bounce(q, &rq->bio);
         rq->buffer = rq->data = NULL;