From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751605Ab1GRHF6 (ORCPT ); Mon, 18 Jul 2011 03:05:58 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:18075 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750855Ab1GRHF5 convert rfc822-to-8bit (ORCPT ); Mon, 18 Jul 2011 03:05:57 -0400 Message-Id: <4E23F76D020000780004DCD9@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 8.0.1 Date: Mon, 18 Jul 2011 08:05:49 +0100 From: "Jan Beulich" To: , "Keir Fraser" , "Konrad Rzeszutek Wilk" , Cc: , , Subject: Re: [Xen-devel] [PATCH] xen: update machine_to_phys_order on resume References: <4E20873F020000780007307B@nat28.tlf.novell.com> In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> On 15.07.11 at 20:23, Keir Fraser wrote: > On 15/07/2011 18:30, "Jan Beulich" wrote: > >> Actually, one more thought: What's the purpose of this hypercall if >> it is set in stone what values it ought to return? Isn't a guest using >> it (supposed to be) advertising that it can deal with the values being >> variable (and it was just overlooked so far that this doesn't only >> include varying values from boot to boot, but also migration)? Or in >> other words, if we found a need to relocate the M2P table or grow >> its static maximum size, it would be impossible to migrate guests >> from an old to a new hypervisor. > > Fair point. There has to be a static fallback set of return values for old > guests. Hmm, in my reading the two sentences sort of contradict each other. That is, I'm not certain what route we want to go here: Keep things the way they are after 23706:3dd399873c9e, and introduce a completely new discovery mechanism if we find it necessary to change the M2P table's location and/or size, including a mechanism for a guest to announce it's capable of dealing with that? If so, I think we ought to add a comment to the hypercall implementation documenting that its return values must not be changed (and why). Jan