From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754601AbaIDXTi (ORCPT ); Thu, 4 Sep 2014 19:19:38 -0400 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:49464 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751272AbaIDXTg (ORCPT ); Thu, 4 Sep 2014 19:19:36 -0400 X-Sasl-enc: NNSnaCmmZzwMuM1Ij/oUwLsOYVTEy4ZXcT/k0pwY/ZKj 1409872775 Date: Thu, 4 Sep 2014 20:19:23 -0300 From: Henrique de Moraes Holschuh To: "H. Peter Anvin" Cc: Toshi Kani , tglx@linutronix.de, mingo@redhat.com, akpm@linuxfoundation.org, arnd@arndb.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jgross@suse.com, stefan.bader@canonical.com, luto@amacapital.net, konrad.wilk@oracle.com Subject: Re: [PATCH 1/5] x86, mm, pat: Set WT to PA4 slot of PAT MSR Message-ID: <20140904231923.GA15320@khazad-dum.debian.net> References: <1409855739-8985-1-git-send-email-toshi.kani@hp.com> <1409855739-8985-2-git-send-email-toshi.kani@hp.com> <20140904201123.GA9116@khazad-dum.debian.net> <5408C9C4.1010705@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5408C9C4.1010705@zytor.com> X-GPG-Fingerprint1: 4096R/39CB4807 C467 A717 507B BAFE D3C1 6092 0BD9 E811 39CB 4807 X-GPG-Fingerprint2: 1024D/1CDB0FE3 5422 5C61 F6B7 06FB 7E04 3738 EE25 DE3F 1CDB 0FE3 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 Thu, 04 Sep 2014, H. Peter Anvin wrote: > On 09/04/2014 01:11 PM, Henrique de Moraes Holschuh wrote: > > I am worried of uncharted territory, here. I'd actually advocate for not > > enabling the upper four PAT entries on IA-32 at all, unless Windows 9X / XP > > is using them as well. Is this a real concern, or am I being overly > > cautious? > > It is extremely unlikely that we'd have PAT issues in 32-bit mode and > not in 64-bit mode on the same CPU. Sure, but is it really a good idea to enable this on the *old* non-64-bit capable processors (note: I don't mean x86-64 processors operating in 32-bit mode) ? > As far as I know, the current blacklist rule is very conservative due to > lack of testing more than anything else. I was told that much in 2009 when I asked why cpuid 0x6d8 was blacklisted from using PAT :-) -- "One disk to rule them all, One disk to find them. One disk to bring them all and in the darkness grind them. In the Land of Redmond where the shadows lie." -- The Silicon Valley Tarot Henrique Holschuh