Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754128AbYBIPOK (ORCPT ); Sat, 9 Feb 2008 10:14:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753270AbYBIPNm (ORCPT ); Sat, 9 Feb 2008 10:13:42 -0500 Received: from smtp-out01.alice-dsl.net ([88.44.60.11]:52778 "EHLO smtp-out01.alice-dsl.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751291AbYBIPN2 (ORCPT ); Sat, 9 Feb 2008 10:13:28 -0500 Date: Sat, 9 Feb 2008 16:13:22 +0100 From: Andi Kleen To: Thomas Gleixner Cc: Andi Kleen , mingo@elte.hu, linux-kernel@vger.kernel.org Subject: Re: [PATCH] [1/5] CPA: Split static_protections into required_static_prot and advised_static_prot Message-ID: <20080209151322.GB6773@basil.nowhere.org> References: <20080208536.837219990@suse.de> <20080208163612.D76421B41AA@basil.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.13 (2006-08-11) X-OriginalArrivalTime: 09 Feb 2008 15:07:02.0159 (UTC) FILETIME=[6CB571F0:01C86B2D] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1321 Lines: 30 On Sat, Feb 09, 2008 at 03:56:02PM +0100, Thomas Gleixner wrote: > On Fri, 8 Feb 2008, Andi Kleen wrote: > > There is a big difference between NX and RO. NX absolutely has to be cleared > > or the kernel will fail while RO just can be set, but does not need to. > > And for a large page area not setting NX if there is a area below > > it that needs it is essential, while making it ro is optional again. Optional as in it doesn't need to be forced. > > No, it's not optional. Making the PMD RO will write protect all 4k > PTEs below independent of their setting. So there is the same > restriction as we have with NX. If there is a boundary between a RO area and a RW area and you want to map it with 2MB pages then NX is required, but RO is optional on the page and if you prefer TLB use minimalization over debugging it is optional. Is it clear now? Note the behaviour for pageattr and thus DEBUG_RODATA / debugging sitations where you don't care about your TLB this does not change, this makes only a difference for the initial init_32 direct mapping setup. -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/