From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756651Ab3J1N6x (ORCPT ); Mon, 28 Oct 2013 09:58:53 -0400 Received: from mail.skyhub.de ([78.46.96.112]:59325 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756380Ab3J1N6v (ORCPT ); Mon, 28 Oct 2013 09:58:51 -0400 Date: Mon, 28 Oct 2013 14:58:47 +0100 From: Borislav Petkov To: Andreas Werner Cc: Ingo Molnar , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] X86: MM: Add PAT Type write-through in combination with mtrr Message-ID: <20131028135847.GK4314@pd.tnic> References: <20131027173131.GC21868@pd.tnic> <20131027175608.GA1340@thinkpad.fritz.box> <20131027190148.GD21868@pd.tnic> <20131028062946.GA1391@thinkpad.fritz.box> <20131028101749.GA4389@gmail.com> <20131028103428.GA2278@thinkpad.fritz.box> <20131028105731.GF4314@pd.tnic> <20131028112505.GD2278@thinkpad.fritz.box> <20131028114541.GI4314@pd.tnic> <20131028120358.GE2278@thinkpad.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20131028120358.GE2278@thinkpad.fritz.box> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 28, 2013 at 01:03:58PM +0100, Andreas Werner wrote: > > That doesn't mean you can return _PAGE_CACHE_WB for MTRR_TYPE_WRTHROUGH. > > The correct thing to do, IMHO, would be to set the PWT bit in the PTEs > > of those pages comprising your buffer. > > > But why? the combination of PAT=WB and MTRR=WT is allowed isn´t it? > What should i return instead of? Well, since the pat code can't give you PWT, I'm thinking the cleaner thing would be to do it yourself. I.e., allocate a WT buffer with mtrr_add and then set the PWT bit of each page in that buffer. Alternatively, your solution - albeit not that correct - is a simple one and probably could use a good comment in the code explaining why you're doing that if we decide to go that way. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --