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=-2.2 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 3A10FC3A59B for ; Mon, 2 Sep 2019 08:58:55 +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 0FF24215EA for ; Mon, 2 Sep 2019 08:58:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0FF24215EA 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]:34222 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i4iAo-0006Kc-4Z for qemu-devel@archiver.kernel.org; Mon, 02 Sep 2019 04:58:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44343) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i4i9h-0005XY-HX for qemu-devel@nongnu.org; Mon, 02 Sep 2019 04:57:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i4i9f-0001RC-Kx for qemu-devel@nongnu.org; Mon, 02 Sep 2019 04:57:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48010) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i4i9f-0001Od-FG; Mon, 02 Sep 2019 04:57:43 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6FFEF3084212; Mon, 2 Sep 2019 08:57:41 +0000 (UTC) Received: from redhat.com (ovpn-112-33.ams2.redhat.com [10.36.112.33]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0052A6012E; Mon, 2 Sep 2019 08:57:39 +0000 (UTC) Date: Mon, 2 Sep 2019 09:57:36 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: David Gibson Message-ID: <20190902085736.GB30123@redhat.com> References: <20190830161345.22436-1-lvivier@redhat.com> <20190830163413.GH4674@redhat.com> <20190830194543.6c1f5776@bahia.lan> <20190902062718.GG415@umbus.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190902062718.GG415@umbus.fritz.box> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Mon, 02 Sep 2019 08:57:41 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH] pseries: do not allow memory-less/cpu-less NUMA node 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Laurent Vivier , qemu-ppc@nongnu.org, Greg Kurz , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Sep 02, 2019 at 04:27:18PM +1000, David Gibson wrote: > On Fri, Aug 30, 2019 at 07:45:43PM +0200, Greg Kurz wrote: > > On Fri, 30 Aug 2019 17:34:13 +0100 > > Daniel P. Berrang=C3=A9 wrote: > >=20 > > > On Fri, Aug 30, 2019 at 06:13:45PM +0200, Laurent Vivier wrote: > > > > When we hotplug a CPU on memory-less/cpu-less node, the linux ker= nel > > > > crashes. > > > >=20 > > > > This happens because linux kernel needs to know the NUMA topology= at > > > > start to be able to initialize the distance lookup table. > > > >=20 > > > > On pseries, the topology is provided by the firmware via the exis= ting > > > > CPUs and memory information. Thus a node without memory and CPU c= annot be > > > > discovered by the kernel. > > > >=20 > > > > To avoid the kernel crash, do not allow to start pseries with emp= ty > > > > nodes. > > >=20 > > > This describes one possible guest OS. Is there any reasonable chanc= e > > > that a non-Linux guest might be able to handle this situation corre= ctly, > > > or do you expect any guest to have the same restriction ? >=20 > That's... a more complicated question than you'd think. >=20 > The problem here is it's not really obvious in PAPR how topology > information for nodes without memory should be described in the device > tree (which is the only way we given that information to the guest). >=20 > It's possible there's some way to encode this information that would > make AIX happy and we just need to fix Linux to cope with that, but > it's not really clear what it would be. >=20 > > I can try to grab an AIX image and give a try, but anyway this looks = like > > a very big hammer to me... :-\ >=20 > I'm not really sure why everyone seems to think losing zero-memory > node capability is such a big deal. It's never worked in practice on > POWER and we can always put it back if we figure out a sensible way to > do it. I'm not that bothered - I just wanted to double check that we were not intentionally breaking a non-Linux guest OS that was known to work today. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|