From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751512AbdILQJx (ORCPT ); Tue, 12 Sep 2017 12:09:53 -0400 Received: from mx2.suse.de ([195.135.220.15]:46689 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751411AbdILQJw (ORCPT ); Tue, 12 Sep 2017 12:09:52 -0400 Subject: Re: [PATCH 2/4] xen: limit grant v2 interface to the v1 functionality To: Boris Ostrovsky , linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org References: <20170908144849.2958-1-jgross@suse.com> <20170908144849.2958-3-jgross@suse.com> <8c87dc06-bbc8-5279-d135-d3351032913d@suse.com> <2777c0f8-7555-fbf3-6e18-81cea2fd1a39@oracle.com> From: Juergen Gross Message-ID: <7dd99241-f771-9fa2-8a6a-ce019dbe08b6@suse.com> Date: Tue, 12 Sep 2017 18:09:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <2777c0f8-7555-fbf3-6e18-81cea2fd1a39@oracle.com> Content-Type: text/plain; charset=windows-1252 Content-Language: de-DE Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/09/17 18:05, Boris Ostrovsky wrote: > On 09/12/2017 11:50 AM, Juergen Gross wrote: >> On 12/09/17 17:44, Boris Ostrovsky wrote: >>> On 09/08/2017 10:48 AM, Juergen Gross wrote: >>>> As there is currently no user for sub-page grants or transient grants >>>> remove that functionality. This at once makes it possible to switch >>>> from grant v2 to grant v1 without restrictions, as there is no loss of >>>> functionality other than the limited frame number width related to >>>> the switch. >>> But isn't that ABI violation? v2 is expected to support this (XSAs >>> notwithstanding) >> No, I don't think so. >> >> The hypervisor still supports it, but the domU (or dom0) isn't required >> to make use of all the features IMHO. Or are you aware of any backend >> querying the grant version of a frontend and acting in another way if v2 >> is detected? > > I am not aware of any but that doesn't mean that they don't (or won't) > exist. But isn't the frontend the one which is defining what is granted in which way? How should there be an ABI breakage when the frontend just isn't using sub-page or transitive grants? Juergen