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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2B55CC33C9E for ; Tue, 28 Jan 2020 11:25:10 +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 EB0D924681 for ; Tue, 28 Jan 2020 11:25:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LRC4UmHl" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB0D924681 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]:57454 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iwOzV-0002Fp-5Z for qemu-devel@archiver.kernel.org; Tue, 28 Jan 2020 06:25:09 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:60178) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iwOys-0001q1-H7 for qemu-devel@nongnu.org; Tue, 28 Jan 2020 06:24:31 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iwOyq-0003uT-S2 for qemu-devel@nongnu.org; Tue, 28 Jan 2020 06:24:30 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:27811 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iwOyq-0003tJ-OY for qemu-devel@nongnu.org; Tue, 28 Jan 2020 06:24:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580210668; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=C9EhQdcctfHBal6s7JqbJIBfivGfxtbRt7Hg27OolxI=; b=LRC4UmHldPrtsaPrMPc7LOovzty0sTkadt38EHWIAXWeaKJqYS3uLkp5CI4hvF8MSLbhkK RagWAzH+Ms76wjeMwDPU94Gs8PhnIMA/eJcqnMMDu3mVfpJCaVnClZ1Ug12UdBHMo/+491 CKPfOkIFlF2fHERADc1CUbinVn3pbAc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-423-Fzc_iIJhN2WyDbOjwCyi5w-1; Tue, 28 Jan 2020 06:24:26 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 33841800D4C; Tue, 28 Jan 2020 11:24:25 +0000 (UTC) Received: from gondolin (ovpn-116-186.ams2.redhat.com [10.36.116.186]) by smtp.corp.redhat.com (Postfix) with ESMTP id 801CB5D9C9; Tue, 28 Jan 2020 11:24:21 +0000 (UTC) Date: Tue, 28 Jan 2020 12:24:18 +0100 From: Cornelia Huck To: Collin Walling Subject: Re: [PATCH v6 2/2] s390: diagnose 318 info reset and migration support Message-ID: <20200128122418.7533f4bb.cohuck@redhat.com> In-Reply-To: References: <1579904044-20790-1-git-send-email-walling@linux.ibm.com> <1579904044-20790-3-git-send-email-walling@linux.ibm.com> <20200127124756.3627f754.cohuck@redhat.com> <1cbd5354-d9ca-a10e-0053-a61a00223f53@linux.ibm.com> <20200127183504.2de2654f.cohuck@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-MC-Unique: Fzc_iIJhN2WyDbOjwCyi5w-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 207.211.31.120 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: borntraeger@de.ibm.com, qemu-s390x@nongnu.org, david@redhat.com, qemu-devel@nongnu.org, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 27 Jan 2020 18:05:36 -0500 Collin Walling wrote: > On 1/27/20 12:35 PM, Cornelia Huck wrote: > > On Mon, 27 Jan 2020 11:39:02 -0500 > > Collin Walling wrote: > > > >> On 1/27/20 6:47 AM, Cornelia Huck wrote: > >>> On Fri, 24 Jan 2020 17:14:04 -0500 > >>> Collin Walling wrote: > >>> > > [...] > > >>>> > >>>> The availability of this instruction is determined by byte 134, bit 0 > >>>> of the Read Info block. This coincidentally expands into the space used > >>> > >>> "SCLP Read Info" > >>> > >>>> for CPU entries by taking away one byte, which means VMs running with > >>>> the diag318 capability will not be able to retrieve information regarding > >>>> the 248th CPU. This will not effect performance, and VMs can still be > >>>> ran with 248 CPUs. > >>> > >>> Are there other ways in which that might affect guests? I assume Linux > >>> can deal with it? Is it ok architecture-wise? > >>> > >>> In any case, should go into the patch description :) > >>> > >> > >> Same as above. I'll try to provide more information regarding what happens > >> here in my next reply. > > > > I think you can lift some stuff from the cover letter. > > > > Here's what I found out: > > Each CPU entry holds info regarding the CPU's address / ID as well as an > indication of the availability of certain CPU features. With these patches, > we lose a CPU entry for one CPU (essentially what would be the CPU at the > tail-end of the list). This CPU exists, but is essentially in limbo... the > machine cannot access any information regarding it. s/machine/guest/ ? > > So, a VM can run with the original N max CPUs, but in reality we can only > utilize n-1. s/we/the guest/ ? With those changes, it makes sense to put your explanations into the patch description (for later reference). > > >> > >>>> > > [...] > >