Here are another couple of places where 8 sectors/page is assumed,

which I missed in my first patch.
Signed-off-by: Matthew Chapman <matthewc@hp.com>

linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c

@@ -379,7 +379,7 @@ static void dispatch_probe(blkif_t *blkif, blkif_request_t *req)
 
     /* Make sure the buffer is page-sized. */
     if ( (blkif_first_sect(req->frame_and_sects[0]) != 0) ||
-         (blkif_last_sect(req->frame_and_sects[0]) != 7) )
+         (blkif_last_sect(req->frame_and_sects[0]) != ((PAGE_SIZE/512)-1)) )
         goto out;
 
 #ifdef CONFIG_XEN_BLKDEV_GRANT

linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c

@@ -775,7 +775,7 @@ static int blkif_queue_request(unsigned long   id,
     /* Buffer must be sector-aligned. Extent mustn't cross a page boundary. */
     if ( unlikely((buffer_ma & ((1<<9)-1)) != 0) )
         BUG();
-    if ( lsect > 7 )
+    if ( lsect > ((PAGE_SIZE/512)-1) )
         BUG();
 
     buffer_ma &= PAGE_MASK;