Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934590AbbGVPhf (ORCPT ); Wed, 22 Jul 2015 11:37:35 -0400 Received: from prv-mh.provo.novell.com ([137.65.248.74]:50818 "EHLO prv-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932693AbbGVPhe convert rfc822-to-8bit (ORCPT ); Wed, 22 Jul 2015 11:37:34 -0400 X-Greylist: delayed 1203 seconds by postgrey-1.27 at vger.kernel.org; Wed, 22 Jul 2015 11:37:34 EDT Message-Id: <55AFD027020000780009424E@prv-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.0.1 Date: Wed, 22 Jul 2015 09:17:27 -0600 From: "Jan Beulich" To: "Toshi Kani" Cc: , , , , Subject: Re: [PATCH] x86: adjust default caching mode translation tables References: <55ACC3660200007800092E62@mail.emea.novell.com> <1437517740.3214.247.camel@hp.com> In-Reply-To: <1437517740.3214.247.camel@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1437 Lines: 33 >>> On 22.07.15 at 00:29, wrote: > On Mon, 2015-07-20 at 08:46 +0100, Jan Beulich wrote: >> Make WT really mean WT (rather than UC). >> >> I can't see why commit 9cd25aac1f ("x86/mm/pat: Emulate PAT when it is >> disabled") didn't make this match its changes to pat_init(). > > No, the default values need to be set to the fallback types, i.e. minimal > supported mode. For WC and WT, UC is the fallback type. But why would that be? > When PAT is disabled, pat_init() does update the tables below to enable WT > per the default BIOS setup. However, when PAT is enabled, but CPU has PAT > -errata, WT falls back to UC per the default values. PAT related errata I'm aware of are related to either page size or the number of bits used to index into the PAT MSR, but never to a particular memory type. Are you saying there are errata which make use of WT or WC impossible altogether? Otherwise I would have thought (even more so in the absence of any comment saying otherwise - "minimal supported modes" doesn't really say on what basis the set is the minimal one) that the mode systems come up in (compatible with pre-PAT) ought to be what the tables express. Jan -- 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/