From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261401AbVBWDg7 (ORCPT ); Tue, 22 Feb 2005 22:36:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261403AbVBWDg7 (ORCPT ); Tue, 22 Feb 2005 22:36:59 -0500 Received: from gate.crashing.org ([63.228.1.57]:48866 "EHLO gate.crashing.org") by vger.kernel.org with ESMTP id S261401AbVBWDg4 (ORCPT ); Tue, 22 Feb 2005 22:36:56 -0500 Subject: [PATCH] ppc32: kernel mapping breakage From: Benjamin Herrenschmidt To: Andrew Morton , Linus Torvalds Cc: linuxppc-dev list , Linux Kernel list Content-Type: text/plain Date: Wed, 23 Feb 2005 14:35:56 +1100 Message-Id: <1109129756.5326.181.camel@gaston> Mime-Version: 1.0 X-Mailer: Evolution 2.0.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi ! Christoph Lameter's patch that change page allocators to use GFP_ZERO broke ppc32 in a subtle way. Our allocator is designed to work before mem_init_done, in which cases it uses a ppc specific early_get_page() which doesn't return zeroed pages. However, he removed the call to clear_page() unconditionally, thus causing the kernel initial page tables to have random data in them. They are initialized with set_pte, which means it's _mostly_ harmless, except that set_pte on ppc32 preserves the _PAGE_HASHPTE bit, thus we end up with random bits there, which can cause issues with further manipulation of the kernel page tables and will slow down all hash faults to them causing unnecessary searches. Please apply in 2.6.11 if still possible ... Signed-off-by: Benjamin Herrenschmidt Index: linux-work/arch/ppc/mm/pgtable.c =================================================================== --- linux-work.orig/arch/ppc/mm/pgtable.c 2005-01-24 17:09:23.000000000 +1100 +++ linux-work/arch/ppc/mm/pgtable.c 2005-02-23 14:31:41.000000000 +1100 @@ -107,8 +107,11 @@ ptepage->mapping = (void *) mm; ptepage->index = address & PMD_MASK; } - } else + } else { pte = (pte_t *)early_get_page(); + if (pte) + clear_page(pte); + } return pte; }