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=-5.5 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 3ABDBC433E1 for ; Fri, 17 Jul 2020 14:06:22 +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 09E932067D for ; Fri, 17 Jul 2020 14:06:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 09E932067D Authentication-Results: mail.kernel.org; dmarc=fail (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 1jwR03-00053g-5Y; Fri, 17 Jul 2020 14:06:07 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jwR02-00053b-35 for xen-devel@lists.xenproject.org; Fri, 17 Jul 2020 14:06:06 +0000 X-Inumbo-ID: a646a4c4-c836-11ea-9612-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id a646a4c4-c836-11ea-9612-12813bfff9fa; Fri, 17 Jul 2020 14:06:03 +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 46A83AD89; Fri, 17 Jul 2020 14:06:07 +0000 (UTC) Subject: Re: RFC: PCI devices passthrough on Arm design proposal To: Bertrand Marquis References: <3F6E40FB-79C5-4AE8-81CA-E16CA37BB298@arm.com> <28899FEF-9DA7-4513-8283-1AC5EFFC6E92@arm.com> <1dd5db2d-98c7-7738-c3d4-d3f098dfe674@suse.com> From: Jan Beulich Message-ID: Date: Fri, 17 Jul 2020 16:06:05 +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: 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: Rahul Singh , Julien Grall , Stefano Stabellini , "xen-devel@lists.xenproject.org" , nd , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 17.07.2020 15:59, Bertrand Marquis wrote: > > >> On 17 Jul 2020, at 15:19, Jan Beulich wrote: >> >> On 17.07.2020 15:14, Bertrand Marquis wrote: >>>> On 17 Jul 2020, at 10:10, Jan Beulich wrote: >>>> On 16.07.2020 19:10, Rahul Singh wrote: >>>>> # Emulated PCI device tree node in libxl: >>>>> >>>>> Libxl is creating a virtual PCI device tree node in the device tree to enable the guest OS to discover the virtual PCI during guest boot. We introduced the new config option [vpci="pci_ecam"] for guests. When this config option is enabled in a guest configuration, a PCI device tree node will be created in the guest device tree. >>>> >>>> I support Stefano's suggestion for this to be an optional thing, i.e. >>>> there to be no need for it when there are PCI devices assigned to the >>>> guest anyway. I also wonder about the pci_ prefix here - isn't >>>> vpci="ecam" as unambiguous? >>> >>> This could be a problem as we need to know that this is required for a guest upfront so that PCI devices can be assigned after using xl. >> >> I'm afraid I don't understand: When there are no PCI device that get >> handed to a guest when it gets created, but it is supposed to be able >> to have some assigned while already running, then we agree the option >> is needed (afaict). When PCI devices get handed to the guest while it >> gets constructed, where's the problem to infer this option from the >> presence of PCI devices in the guest configuration? > > If the user wants to use xl pci-attach to attach in runtime a device to a guest, this guest must have a VPCI bus (even with no devices). > If we do not have the vpci parameter in the configuration this use case will not work anymore. That's what everyone looks to agree with. Yet why is the parameter needed when there _are_ PCI devices anyway? That's the "optional" that Stefano was suggesting, aiui. Jan