1 files changed, 19 insertions, 14 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 03d9c82b0fe7..0ef2971a9e82 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -625,26 +625,31 @@ static inline int ordered_bio_endio(struct request *rq, struct bio *bio,
  *    Different hardware can have different requirements as to what pages
  *    it can do I/O directly to. A low level driver can call
  *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
- *    buffers for doing I/O to pages residing above @page. By default
- *    the block layer sets this to the highest numbered "low" memory page.
+ *    buffers for doing I/O to pages residing above @page.
  **/
 void blk_queue_bounce_limit(request_queue_t *q, u64 dma_addr)
 {
         unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
-
-        /*
-         * set appropriate bounce gfp mask -- unfortunately we don't have a
-         * full 4GB zone, so we have to resort to low memory for any bounces.
-         * ISA has its own < 16MB zone.
-         */
-        if (bounce_pfn < blk_max_low_pfn) {
-                BUG_ON(dma_addr < BLK_BOUNCE_ISA);
+        int dma = 0;
+
+        q->bounce_gfp = GFP_NOIO;
+#if BITS_PER_LONG == 64
+        /* Assume anything <= 4GB can be handled by IOMMU.
+           Actually some IOMMUs can handle everything, but I don't
+           know of a way to test this here. */
+        if (bounce_pfn < (0xffffffff>>PAGE_SHIFT))
+                dma = 1;
+        q->bounce_pfn = max_low_pfn;
+#else
+        if (bounce_pfn < blk_max_low_pfn)
+                dma = 1;
+        q->bounce_pfn = bounce_pfn;
+#endif
+        if (dma) {
                 init_emergency_isa_pool();
                 q->bounce_gfp = GFP_NOIO | GFP_DMA;
-        } else
-                q->bounce_gfp = GFP_NOIO;
-
-        q->bounce_pfn = bounce_pfn;
+                q->bounce_pfn = bounce_pfn;
+        }
 }
 
 EXPORT_SYMBOL(blk_queue_bounce_limit);