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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 A25A4C3A59B for ; Mon, 2 Sep 2019 09:23:59 +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 6F8B1215EA for ; Mon, 2 Sep 2019 09:23:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.b="IVwh7LYw" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F8B1215EA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:34314 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i4iZ3-00062t-DN for qemu-devel@archiver.kernel.org; Mon, 02 Sep 2019 05:23:57 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48110) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i4iXb-0004TP-MS for qemu-devel@nongnu.org; Mon, 02 Sep 2019 05:22:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i4iXa-0005aG-6M for qemu-devel@nongnu.org; Mon, 02 Sep 2019 05:22:27 -0400 Received: from bilbo.ozlabs.org ([203.11.71.1]:56023 helo=ozlabs.org) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i4iXY-0005W5-Nv; Mon, 02 Sep 2019 05:22:26 -0400 Received: by ozlabs.org (Postfix, from userid 1007) id 46MPk43wkrz9sDB; Mon, 2 Sep 2019 19:22:20 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gibson.dropbear.id.au; s=201602; t=1567416140; bh=rHcWX+gA9u27gQcsd4p1fHbfLiq5yWr+Y3Qk59lheyk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IVwh7LYwDWNtryOgyY0XuCHBnVRIJT3jThJlYt+MnYfSGK0sjrOcNhtSjXspK7qbu Gxf3RIbG0uGjxmn62jVVXHHE8yPwNd0KZ07auBC4Yy20nl5JK9W00Nvo1ZnbcYBf34 fkhOI/313cv6eOszAjKw/L5bnx+5V4a58L7Xh6ac= Date: Mon, 2 Sep 2019 19:11:11 +1000 From: David Gibson To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Message-ID: <20190902091111.GA30674@umbus.fritz.box> References: <20190830161345.22436-1-lvivier@redhat.com> <20190830163413.GH4674@redhat.com> <20190830194543.6c1f5776@bahia.lan> <20190902062718.GG415@umbus.fritz.box> <20190902085736.GB30123@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="TB36FDmn/VVEgNH/" Content-Disposition: inline In-Reply-To: <20190902085736.GB30123@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 203.11.71.1 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: , 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" --TB36FDmn/VVEgNH/ Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Sep 02, 2019 at 09:57:36AM +0100, Daniel P. Berrang=E9 wrote: > 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=E9 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 chance > > > > 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. >=20 > 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. There are no non-Linux guests that are known to work today, unless you count the kvm-unit-tests micro-OS. AIX support is coming along, but it's by no means established. --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --TB36FDmn/VVEgNH/ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEdfRlhq5hpmzETofcbDjKyiDZs5IFAl1s3KsACgkQbDjKyiDZ s5Jr7RAAgIyoSw6oXICBMIINg53Zriz0IgENAhXj49k+W0qgUZ234JRfmD13YjYf P4ao8ss+DnwGZ6AYXS5FPSG6LEXnR7NAGsNBjaeVzFjcnUP7Mr6+7uOWs9TjaTmp jD48wovDW2ZRMYCVk0QZOAlGM+aQ9O/w/hoRPGRxyKcp+ZP9I8q+Dnkw9WOVHFNA 0wcsXJGRb/zGedvUveFnA7uQu7F8Of4YzRjS6ecs5dErBSAWMQJMFU7xi6xxkQ8X kDUx1iOoVOci97no02WnHkLfFhuSzq0+B6V7W+io1Sf5QtZJvxG1n8lv13onJR4M 9SE4u9iCpBFXJ69muxquTqFQVO6Ob3G8rFsD2HGIvIGwCSzELGJUjvs8BLunF6kZ MJIcj2bopMwweDRV9kkLlvrK0sDXETs0cSItGQjPKIwh6id/CgZQlwHi4goyJVub X0y0+5hK+UDElN7pGXoJoLjJ5CmRzRSWeJFv1HZHRTRH8tUL0gqyQOea8hxESitW P+JalkSa1PQ8xorPu9EeAfRKTNbT6QalGbJ9nskd9QB2gVQEX+kLf4CW22I0tRbG vrkN9LzkkPBB1foJXrlJL3boaBQL9Xzwg5+djk9jpgDc3hlSKZQF5mIbhkeW+jFd hx8VynDA5+j5TICksRi/Rr5e1FJPI54uh1AZx46Hw4zxCxb47GM= =zXF5 -----END PGP SIGNATURE----- --TB36FDmn/VVEgNH/--