This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


[Xen-devel] Re: [PATCH 12/12] xen/mtrr: Add mtrr_if support for Xen mtrr

To: "H. Peter Anvin" <hpa@xxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 12/12] xen/mtrr: Add mtrr_if support for Xen mtrr
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 28 Sep 2010 11:58:05 -0700
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, "sct@xxxxxxxxxx" <sct@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Delivery-date: Tue, 28 Sep 2010 12:01:00 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4CA23800.4020409@xxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <alpine.DEB.2.00.1009281217540.2864@kaball-desktop> <1285676218-26218-12-git-send-email-stefano.stabellini@xxxxxxxxxxxxx> <20100928123925.GA18208@xxxxxxx> <alpine.DEB.2.00.1009281455300.2864@kaball-desktop> <4CA2223B.9040400@xxxxxxxx> <4CA22C3C.3020209@xxxxxxxxx> <4CA2302C.3000201@xxxxxxxx> <4CA231A8.5000100@xxxxxxxxx> <4CA232EF.3080906@xxxxxxxx> <4CA23800.4020409@xxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100907 Fedora/3.1.3-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.3
 On 09/28/2010 11:46 AM, H. Peter Anvin wrote:
> Well, we're specifically talking about a virtual machine which has
> direct access to hardware, so it is concerned about the real physical
> memory properties of real physical pages.  If we can assume that
> BIOS/Xen will always set up MTRR correctly then there shouldn't be any
> need for the kernel to modify the MTRR itself.  How true is that in
> general?  I don't know, but if we could rely on BIOS then there'd never
> be a need to touch MTRR, would there?
> Well, in the past MTRRs were abused for device properties mainly by the
> X server, but other than that, no, not really.  The other thing we do is
> the MTRR cleanup (which doesn't involve /proc/mtrr) to deal with
> brokenness in the BIOS setup, but that really belongs in the hypervisor
> in your case since it fundamentally affects how memory is handled.

Yeah, the hypervisor should definitely deal with that.  I have no
problem in principle with leaving MTRRs entirely to Xen, but I was just
concerned about possible repercussions.  Certainly when I first did this
work, I was using Fedora 8 whose X server did depend on /proc/mtrr for
good performance.


Xen-devel mailing list