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=-7.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 BB063C07E95 for ; Tue, 13 Jul 2021 15:16:15 +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 759086135F for ; Tue, 13 Jul 2021 15:16:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 759086135F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.155465.286990 (Exim 4.92) (envelope-from ) id 1m3K8f-0005hx-Md; Tue, 13 Jul 2021 15:16:01 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 155465.286990; Tue, 13 Jul 2021 15:16:01 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m3K8f-0005hq-JM; Tue, 13 Jul 2021 15:16:01 +0000 Received: by outflank-mailman (input) for mailman id 155465; Tue, 13 Jul 2021 15:16:01 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m3K8f-0005hI-8a for xen-devel@lists.xenproject.org; Tue, 13 Jul 2021 15:16:01 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m3K8a-0007xM-Tw; Tue, 13 Jul 2021 15:15:56 +0000 Received: from [54.239.6.178] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1m3K8a-0007VB-Mn; Tue, 13 Jul 2021 15:15:56 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=83DVCQtIzPbN/ken9uYkOE1EsFwq13Zl6+swGYXNp0E=; b=wdqqw2CUYVMiBKnJ/UvabE1ysj uP0K6opmhc9YELyiYFqzzU9LzKijNYd1b8pfY93OgSZawkIcTLIF9x30PYBfUO9h7M3Oug+shUFhZ 5UqBLBQ7dX7f/LMDjWQ4K3gAoc/X3d8ET8LbmeIzr6ih3GF2fjy+BvSlX4BnuJw+fxAg=; Subject: Re: [PATCH] stubdom: foreignmemory: Fix build after 0dbb4be739c5 To: Juergen Gross , Jan Beulich Cc: Julien Grall , Ian Jackson , Wei Liu , xen-devel@lists.xenproject.org, Andrew Cooper , Costin Lupu References: <20210713092019.7379-1-julien@xen.org> <0698e4b1-8fb9-919e-e9a2-1b135a808e3e@suse.com> <756ba923-17a6-0889-cc7e-bcd43a5eb258@citrix.com> <3505f2da-4c41-f5ca-d775-814d038d5bad@xen.org> <3c819563-b354-5527-050d-f698324d6021@xen.org> <65d35862-304c-7fe3-82de-3ff62f06529a@suse.com> <40c00267-60d2-c0fc-cde4-8ac4ce936f87@suse.com> <69c62b4c-b46f-9eab-8dfd-742c07423424@suse.com> From: Julien Grall Message-ID: Date: Tue, 13 Jul 2021 16:15:54 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Hi Juergen, On 13/07/2021 16:09, Juergen Gross wrote: > On 13.07.21 16:38, Julien Grall wrote: >> Hi Juergen, >> >> On 13/07/2021 15:23, Juergen Gross wrote: >>> On 13.07.21 16:19, Julien Grall wrote: >>>> Hi Jan, >>>> >>>> On 13/07/2021 15:14, Jan Beulich wrote: >>>>>> And I don't think it should be named XC_PAGE_*, but rather >>>>>> XEN_PAGE_*. >>>>> >>>>> Even that doesn't seem right to me, at least in principle. There >>>>> shouldn't >>>>> be a build time setting when it may vary at runtime. IOW on Arm I >>>>> think a >>>>> runtime query to the hypervisor would be needed instead. >>>> >>>> Yes, we want to be able to use the same userspace/OS without >>>> rebuilding to a specific hypervisor page size. >>> >>> This define is used for accessing data of other domains. See the define >>> for XEN_PAGE_SIZE in xen/include/public/io/ring.h >>> >>> So it should be a constant (minimal) page size for all hypervisors and >>> guests of an architecture. >> >> Do you mean the maximum rather than minimal? If you use the minimal >> (4KB), then you would not be able to map the page in the stage-2 if >> the hypervisor is using 64KB. > > But this would mean that the current solution to use XC_PAGE_SIZE is > wrong, as this is 4k. The existing ABI is implicitely based on using the hypervisor page granularity (currently 4KB). There is really no way we can support existing guest on 64KB hypervisor. But if we were going to break them, then we should consider to do one of the following option: 1) use 64KB page granularity for ABI 2) query the hypervisor page granularity at runtime The ideal is 2) because it is more scalable for the future. We also need to consider to extend the PV protocol so the backend and frontend can agree on the page size. Cheers, -- Julien Grall