Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751480AbdIONVe convert rfc822-to-8bit (ORCPT ); Fri, 15 Sep 2017 09:21:34 -0400 Received: from prv-mh.provo.novell.com ([137.65.248.74]:34675 "EHLO prv-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751207AbdIONVc (ORCPT ); Fri, 15 Sep 2017 09:21:32 -0400 Message-Id: <59BBEFFC020000780017B8EF@prv-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.2.2 Date: Fri, 15 Sep 2017 07:21:32 -0600 From: "Jan Beulich" To: "Juergen Gross" Cc: "Andrew Cooper" , , , Subject: Re: [Xen-devel] [PATCH 4/4] xen: select grant interface version References: <20170908144849.2958-1-jgross@suse.com> <20170908144849.2958-5-jgross@suse.com> <7d34f929-b45d-c056-865d-94082312b0bc@suse.com> <17e66ddd-cd08-9749-a27b-ac81bf0d3c5d@suse.com> In-Reply-To: <17e66ddd-cd08-9749-a27b-ac81bf0d3c5d@suse.com> 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 Content-Length: 1030 Lines: 22 >>> On 15.09.17 at 15:00, wrote: > So I've found the data I've searched in the hypervisor. The maximum > frame number to expect can be calculated from max_page, mem_hotplug > and the maximum physical address from cpuid node 0x80000008. If > CONFIG_BIGMEM isn't defined in Xen it is 16TB max. > > The question is how to present this value to a guest. IMHO something > like the maximum address width similar to cpuid node 0x80000008 > would be fine. It could be above width for pv guests and the max. > memory address of the guest for HVM guests (adding a cap for those > wouldn't be the worst idea, I guess). > > What about a new subop of the xen_version hypercall? I don't see how that would be a good fit; instead, with the CPUID similarity you mention, why not provide the information in one of Xen's CPUID leaves? Otoh I wonder whether returning max_page from XENMEM_maximum_ram_page is really a good idea, if later on that value may increase, so perhaps that op should take mem_hotplug into account. Jan