From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B9133C433DF for ; Fri, 31 Jul 2020 10:18:59 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8FA06208E4 for ; Fri, 31 Jul 2020 10:18:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8FA06208E4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k1S7h-0006IB-GX; Fri, 31 Jul 2020 10:18:45 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k1S7f-0006I6-QE for xen-devel@lists.xenproject.org; Fri, 31 Jul 2020 10:18:43 +0000 X-Inumbo-ID: 357022b6-d317-11ea-8e22-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 357022b6-d317-11ea-8e22-bc764e2007e4; Fri, 31 Jul 2020 10:18:42 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D7D68AF95; Fri, 31 Jul 2020 10:18:54 +0000 (UTC) Subject: Re: [PATCH v2] xen/arm: Convert runstate address during hypcall To: Julien Grall References: <4647a019c7b42d40d3c2f5b0a3685954bea7f982.1595948219.git.bertrand.marquis@arm.com> <8d2d7f03-450c-d50c-630b-8608c6d42bb9@suse.com> <1b046f2c-05c8-9276-a91e-fd55ec098bed@suse.com> <1a8bbcc7-9d0c-9669-db7b-e837af279027@suse.com> <73c8ade5-36a3-cc13-80b6-bda89e175cbb@xen.org> From: Jan Beulich Message-ID: <6066b507-f956-8e7a-89f3-b21428b66d65@suse.com> Date: Fri, 31 Jul 2020 12:18:40 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <73c8ade5-36a3-cc13-80b6-bda89e175cbb@xen.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Andrew Cooper , Ian Jackson , George Dunlap , Bertrand Marquis , Xen-devel , nd , Volodymyr Babchuk , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 31.07.2020 12:12, Julien Grall wrote: > On 31/07/2020 07:39, Jan Beulich wrote: >> We're fixing other issues without breaking the ABI. Where's the >> problem of backporting the kernel side change (which I anticipate >> to not be overly involved)? > This means you can't take advantage of the runstage on existing Linux > without any modification. > >> If the plan remains to be to make an ABI breaking change, > > For a theoritical PoV, this is a ABI breakage. However, I fail to see > how the restrictions added would affect OSes at least on Arm. "OSes" covering what? Just Linux? > In particular, you can't change the VA -> PA on Arm without going > through an invalid mapping. So I wouldn't expect this to happen for the > runstate. > > The only part that *may* be an issue is if the guest is registering the > runstate with an initially invalid VA. Although, I have yet to see that > in practice. Maybe you know? I'm unaware of any such use, but this means close to nothing. >> then I >> think this will need an explicit vote. > > I was under the impression that the two Arm maintainers (Stefano and I) > already agreed with the approach here. Therefore, given the ABI breakage > is only affecting Arm, why would we need a vote? The problem here is of conceptual nature: You're planning to make the behavior of a common hypercall diverge between architectures, and in a retroactive fashion. Imo that's nothing we should do even for new hypercalls, if _at all_ avoidable. If we allow this here, we'll have a precedent that people later may (and based on my experience will, sooner or later) reference, to get their own change justified. Jan