From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756585AbbJALvs (ORCPT ); Thu, 1 Oct 2015 07:51:48 -0400 Received: from www.linutronix.de ([62.245.132.108]:33007 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756366AbbJALvp (ORCPT ); Thu, 1 Oct 2015 07:51:45 -0400 Date: Thu, 1 Oct 2015 13:51:05 +0200 (CEST) From: Thomas Gleixner To: Dave Hansen cc: borntraeger@de.ibm.com, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, dave.hansen@linux.intel.com Subject: Re: [PATCH 06/25] x86, pkeys: PTE bits for storing protection key In-Reply-To: <20150928191819.F8EB3C51@viggo.jf.intel.com> Message-ID: References: <20150928191817.035A64E2@viggo.jf.intel.com> <20150928191819.F8EB3C51@viggo.jf.intel.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 28 Sep 2015, Dave Hansen wrote: > From: Dave Hansen > > Previous documentation has referred to these 4 bits as "ignored". > That means that software could have made use of them. But, as > far as I know, the kernel never used them. > > They are still ignored when protection keys is not enabled, so > they could theoretically still get used for software purposes. > > We also implement "empty" versions so that code that references > to them can be optimized away by the compiler when the config > option is not enabled. > > Signed-off-by: Dave Hansen Reviewed-by: Thomas Gleixner