From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753259AbaIEPmL (ORCPT ); Fri, 5 Sep 2014 11:42:11 -0400 Received: from terminus.zytor.com ([198.137.202.10]:48289 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753108AbaIEPmJ (ORCPT ); Fri, 5 Sep 2014 11:42:09 -0400 Message-ID: <5409D99C.10305@zytor.com> Date: Fri, 05 Sep 2014 08:41:16 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 MIME-Version: 1.0 To: Toshi Kani CC: Andy Lutomirski , Henrique de Moraes Holschuh , Thomas Gleixner , Ingo Molnar , akpm@linuxfoundation.org, Arnd Bergmann , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Juergen Gross , Stefan Bader , Konrad Rzeszutek Wilk Subject: Re: [PATCH 1/5] x86, mm, pat: Set WT to PA4 slot of PAT MSR 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> <20140904231923.GA15320@khazad-dum.debian.net> <1409876991.28990.172.camel@misato.fc.hp.com> <1409925614.28990.184.camel@misato.fc.hp.com> <5409D197.2060900@zytor.com> <1409930574.28990.192.camel@misato.fc.hp.com> In-Reply-To: <1409930574.28990.192.camel@misato.fc.hp.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/2014 08:22 AM, Toshi Kani wrote: > On Fri, 2014-09-05 at 08:07 -0700, H. Peter Anvin wrote: >> On 09/05/2014 07:00 AM, Toshi Kani wrote: >>> >>> That's a fine idea, but as Ingo also suggested, I am going to disable >>> this feature on all Pentium 4 models. That should give us a safety >>> margin. Using slot 4 has a benefit that it keeps the PAT setup >>> consistent with Xen. >>> >> >> Slot 4 is also the maximally problematic one, because it is the one that >> might be incorrectly invoked for the page tables themselves. > > Good point. I wonder if Xen folks feel strongly about keeping the PAT > setup consistent with the kernel. If not, we may choose to use slot 6 > (or 7). > Who cares what the Xen folks "feel strongly about"? If strong feelings were a design criterion Xen support would have been pulled from the kernel a long, long time ago. The important thing is how to design for the situation that we currently have to live with. -hpa