From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755096AbZEPSWt (ORCPT ); Sat, 16 May 2009 14:22:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754272AbZEPSWj (ORCPT ); Sat, 16 May 2009 14:22:39 -0400 Received: from outbound-mail-308.bluehost.com ([67.222.53.254]:35484 "HELO outbound-mail-308.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754075AbZEPSWi (ORCPT ); Sat, 16 May 2009 14:22:38 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=default; d=virtuousgeek.org; h=Received:Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References:X-Mailer:Mime-Version:Content-Type:Content-Transfer-Encoding:X-Identified-User; b=pb07Hviw4oH1cvBQkfzlIz6KtsN26grrJh5SIOkOou75IB4PBhHw+fezs6fm7pd1Wjm0NW9i6rLElvForKEGb0fkvp8HJXdrFcy7zbbxkLJhLYuPep6Yk4i+dgSbq19M; Date: Sat, 16 May 2009 11:22:33 -0700 From: Jesse Barnes To: ebiederm@xmission.com (Eric W. Biederman) Cc: Jeremy Fitzhardinge , Ingo Molnar , the arch/x86 maintainers , Linux Kernel Mailing List , Xen-devel Subject: Re: [GIT PULL] xen /proc/mtrr implementation Message-ID: <20090516112233.5cb085c8@jbarnes-g45> In-Reply-To: References: <1242170864-13560-1-git-send-email-jeremy@goop.org> <20090513133021.GA7277@elte.hu> <4A0ADBA2.2020300@goop.org> <20090515182757.GA19256@elte.hu> <4A0DCC11.10307@goop.org> <4A0DFF78.6000501@goop.org> <20090515202250.0f1218ef@jbarnes-g45> X-Mailer: Claws Mail 3.6.1 (GTK+ 2.16.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Identified-User: {10642:box514.bluehost.com:virtuous:virtuousgeek.org} {sentby:smtp auth 75.111.28.251 authed with jbarnes@virtuousgeek.org} Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 15 May 2009 21:26:47 -0700 ebiederm@xmission.com (Eric W. Biederman) wrote: > > FWIW I think supporting the MTRR API in Xen makes sense. There's a > > lot of old code out there that wants it; would be nice if it mostly > > worked, especially at such a minimal cost. It's taken awhile to > > get PAT going (and there are still issues here and there) so having > > the MTRR stuffa available is awfully nice. > > I won't argue that having MTRRs when you can makes sense. It is a bit > weird in a vitalized system. At a practical level there are an > increasing number of systems for which MTRRs are unusable because the > BIOS sets up overlapping mtrrs. With cheap entry level systems > shipping with 4G I expect it is becoming a majority of systems. Yeah, MTRRs definitely have issues too; as you say on many recent machines they're tougher to use. Either we need to reprogram them to free some up for WC mappings, or use PAT. But that's a relatively recent development (last year or two I think?). This is really about what software Xen wants to support though. You can say, "it would be easier for you to just support new software that doesn't use MTRRs," and you might be right, but supporting older stuff doesn't appear that difficult, and it sounds like something they want to do. -- Jesse Barnes, Intel Open Source Technology Center