From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oa0-f47.google.com (mail-oa0-f47.google.com [209.85.219.47]) by kanga.kvack.org (Postfix) with ESMTP id 89A356B00B3 for ; Wed, 10 Sep 2014 17:35:50 -0400 (EDT) Received: by mail-oa0-f47.google.com with SMTP id i7so13615305oag.6 for ; Wed, 10 Sep 2014 14:35:50 -0700 (PDT) Received: from g6t1524.atlanta.hp.com (g6t1524.atlanta.hp.com. [15.193.200.67]) by mx.google.com with ESMTPS id m2si4572671oes.100.2014.09.10.14.35.49 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 10 Sep 2014 14:35:49 -0700 (PDT) Message-ID: <1410384315.28990.308.camel@misato.fc.hp.com> Subject: Re: [PATCH v2 2/6] x86, mm, pat: Change reserve_memtype() to handle WT From: Toshi Kani Date: Wed, 10 Sep 2014 15:25:15 -0600 In-Reply-To: References: <1410367910-6026-1-git-send-email-toshi.kani@hp.com> <1410367910-6026-3-git-send-email-toshi.kani@hp.com> <1410377428.28990.260.camel@misato.fc.hp.com> <5410B10A.4030207@zytor.com> <1410381050.28990.295.camel@misato.fc.hp.com> <1410383484.28990.303.camel@misato.fc.hp.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Andrew Morton , Arnd Bergmann , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Juergen Gross , Stefan Bader , Henrique de Moraes Holschuh , Yigal Korman , Konrad Rzeszutek Wilk On Wed, 2014-09-10 at 14:27 -0700, Andy Lutomirski wrote: > On Wed, Sep 10, 2014 at 2:11 PM, Toshi Kani wrote: > > On Wed, 2014-09-10 at 14:06 -0700, Andy Lutomirski wrote: > >> On Wed, Sep 10, 2014 at 1:30 PM, Toshi Kani wrote: > >> > On Wed, 2014-09-10 at 13:14 -0700, H. Peter Anvin wrote: > >> >> On 09/10/2014 12:30 PM, Toshi Kani wrote: > >> >> > > >> >> > When WT is unavailable due to the PAT errata, it does not fail but gets > >> >> > redirected to UC-. Similarly, when PAT is disabled, WT gets redirected > >> >> > to UC- as well. > >> >> > > >> >> > >> >> But on pre-PAT hardware you can still do WT. > >> > > >> > Yes, if we manipulates the bits directly, but such code is no longer > >> > allowed for PAT systems. The PAT-based kernel interfaces won't work for > >> > pre-PAT systems, and therefore requests are redirected to UC- on such > >> > systems. > >> > > >> > >> Right, the PWT bit. Forgot about that. > >> > >> I wonder whether it would make sense to do some followup patches to > >> replace the current support for non-PAT machines with a "PAT" and > >> corresponding reverse map that exactly matches the mapping when PAT is > >> disabled. These patches are almost there. > > > > That's possible, but the only benefit is that we can enable WT on > > pre-PAT systems, which I do not think anyone cares now... WB & UC work > > on pre-PAT systems. WC & WT need PAT. I think this requirement is > > reasonable. > > It might end up being a cleanup, though. A whole bunch of > rarely-exercised if (!pat_enabled) things would go away. Good point. I will work on it. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org