From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f170.google.com (mail-lb0-f170.google.com [209.85.217.170]) by kanga.kvack.org (Postfix) with ESMTP id AB4456B00B1 for ; Wed, 10 Sep 2014 17:27:53 -0400 (EDT) Received: by mail-lb0-f170.google.com with SMTP id u10so5033467lbd.1 for ; Wed, 10 Sep 2014 14:27:52 -0700 (PDT) Received: from mail-la0-f51.google.com (mail-la0-f51.google.com [209.85.215.51]) by mx.google.com with ESMTPS id rn2si22978818lbc.37.2014.09.10.14.27.51 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 10 Sep 2014 14:27:52 -0700 (PDT) Received: by mail-la0-f51.google.com with SMTP id gi9so9773442lab.38 for ; Wed, 10 Sep 2014 14:27:51 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1410383484.28990.303.camel@misato.fc.hp.com> 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> From: Andy Lutomirski Date: Wed, 10 Sep 2014 14:27:31 -0700 Message-ID: Subject: Re: [PATCH v2 2/6] x86, mm, pat: Change reserve_memtype() to handle WT Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Toshi Kani 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, 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. --Andy -- 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