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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 71918C4360C for ; Thu, 10 Oct 2019 16:20:54 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 497072067B for ; Thu, 10 Oct 2019 16:20:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 497072067B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41970 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIbBN-0008Al-2Q for qemu-devel@archiver.kernel.org; Thu, 10 Oct 2019 12:20:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41552) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIb6D-000330-5W for qemu-devel@nongnu.org; Thu, 10 Oct 2019 12:15:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iIb6C-0000XY-33 for qemu-devel@nongnu.org; Thu, 10 Oct 2019 12:15:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58064) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iIb6B-0000Wt-Sp for qemu-devel@nongnu.org; Thu, 10 Oct 2019 12:15:32 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 260201056F83; Thu, 10 Oct 2019 16:15:31 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-120-48.rdu2.redhat.com [10.10.120.48]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8A4126092F; Thu, 10 Oct 2019 16:15:22 +0000 (UTC) Subject: Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg To: "Michael S. Tsirkin" , Igor Mammedov References: <20191008105259.5378-1-lersek@redhat.com> <20191008105259.5378-4-lersek@redhat.com> <20191008175931.483af366@redhat.com> <20191010055733-mutt-send-email-mst@kernel.org> From: Laszlo Ersek Message-ID: <55d7aaf3-4f21-c120-a867-6988bcca678e@redhat.com> Date: Thu, 10 Oct 2019 18:15:21 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20191010055733-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.64]); Thu, 10 Oct 2019 16:15:31 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Richard Henderson , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu devel list , Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/10/19 12:01, Michael S. Tsirkin wrote: > On Tue, Oct 08, 2019 at 05:59:31PM +0200, Igor Mammedov wrote: >> So far there were no need for it as all possible cpus are >> described in ACPI tables passed to guest, but I'm not going >> to suggest to parse them on firmware side as it's too complicated :) > > We can always add a QEMU specific data table by the way. > Format would be up to us and would be easy to parse. > I don't see a big advantage as compared to fw cfg though. I'd like to comment just on this part. *If* we decide to expose the information through some kind of data table (as opposed to the modern CPU hotplug register block), then the representation *must* be a dedicated fw_cfg blob. It cannot be an ACPI table. The reason is that *selecting* the fw_cfg blob that contains the ACPI linker/loader script is a very specific action (it re-generates the ACPI payload, with dependencies on assigned PCI resources). Therefore, it is done in a super-particular spot in the firmware. On the other hand, the "possible CPUs count" is needed much earlier than that. I need to fetch that info way before PCI resource assignment appears on the radar. So please let us stick with "ACPI is only for the guest OS to read" rule -- it's not only a parsing convenience for the firmware, but a real necessity. Thanks Laszlo