IB/mthca: Clear ICM pages before handing to FW

Current memfree FW has a bug which in some cases, assumes that ICM
pages passed to it are cleared.  This patch uses __GFP_ZERO to
allocate all ICM pages passed to the FW.  Once firmware with a fix is
released, we can make the workaround conditional on firmware version.

This fixes the bug reported by Arthur Kepner <akepner@sgi.com> here:
http://lists.openfabrics.org/pipermail/general/2008-May/050026.html

Cc: <stable@kernel.org>
Signed-off-by: Eli Cohen <eli@mellanox.co.il>

[ Rewritten to be a one-liner using __GFP_ZERO instead of vmap()ing
  ICM memory and memset()ing it to 0. - Roland ]
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_memfree.c

@@ -109,7 +109,11 @@ static int mthca_alloc_icm_pages(struct scatterlist *mem, int order, gfp_t gfp_m
 {
 	struct page *page;
 
-	page = alloc_pages(gfp_mask, order);
+	/*
+	 * Use __GFP_ZERO because buggy firmware assumes ICM pages are
+	 * cleared, and subtle failures are seen if they aren't.
+	 */
+	page = alloc_pages(gfp_mask | __GFP_ZERO, order);
 	if (!page)
 		return -ENOMEM;