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=-7.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 03EB1C433E0 for ; Mon, 18 Jan 2021 17:43:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C55C122CAD for ; Mon, 18 Jan 2021 17:43:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2436619AbhARRmc (ORCPT ); Mon, 18 Jan 2021 12:42:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:52797 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2436590AbhARRlI (ORCPT ); Mon, 18 Jan 2021 12:41:08 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610991577; 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=X15+VkT7M78mSFfo/qnb5Wzv8facU/FgWbJCl9EtkQE=; b=Up9utAk+cCEhrj66DhcJ1L7Fdu8Tc7OiJrKrAeATHMnzo6h9L0QgNKoIN6yk8AbeFzvTQ4 ELg09cCa/aBOn04gsU/hyyj+nFj4OJAUUcsTDbW+IndpIS1GM0DOSnqn0Zkv/C7niuUzJq 3E+hYSASh8+OMZpK5HONFZf6nAl+Zr4= 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-323-1P1DwBnRNpi7kX2HgDLh5w-1; Mon, 18 Jan 2021 12:39:33 -0500 X-MC-Unique: 1P1DwBnRNpi7kX2HgDLh5w-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id A789D1005D4E; Mon, 18 Jan 2021 17:39:30 +0000 (UTC) Received: from work-vm (ovpn-115-197.ams2.redhat.com [10.36.115.197]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AB75818F15; Mon, 18 Jan 2021 17:39:15 +0000 (UTC) Date: Mon, 18 Jan 2021 17:39:12 +0000 From: "Dr. David Alan Gilbert" To: David Gibson Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Cornelia Huck , pair@us.ibm.com, brijesh.singh@amd.com, kvm@vger.kernel.org, "Michael S. Tsirkin" , Ram Pai , qemu-devel@nongnu.org, frankja@linux.ibm.com, david@redhat.com, mdroth@linux.vnet.ibm.com, Halil Pasic , borntraeger@de.ibm.com, thuth@redhat.com, Eduardo Habkost , Richard Henderson , Greg Kurz , qemu-s390x@nongnu.org, rth@twiddle.net, Marcelo Tosatti , qemu-ppc@nongnu.org, pbonzini@redhat.com Subject: Re: [for-6.0 v5 11/13] spapr: PEF: prevent migration Message-ID: <20210118173912.GF9899@work-vm> References: <20201218124111.4957eb50.cohuck@redhat.com> <20210104071550.GA22585@ram-ibm-com.ibm.com> <20210104134629.49997b53.pasic@linux.ibm.com> <20210104184026.GD4102@ram-ibm-com.ibm.com> <20210105115614.7daaadd6.pasic@linux.ibm.com> <20210105204125.GE4102@ram-ibm-com.ibm.com> <20210111175914.13adfa2e.cohuck@redhat.com> <20210113124226.GH2938@work-vm> <20210114112517.GE1643043@redhat.com> <20210114235125.GO435587@yekko.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210114235125.GO435587@yekko.fritz.box> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org * David Gibson (david@gibson.dropbear.id.au) wrote: > On Thu, Jan 14, 2021 at 11:25:17AM +0000, Daniel P. Berrangé wrote: > > On Wed, Jan 13, 2021 at 12:42:26PM +0000, Dr. David Alan Gilbert wrote: > > > * Cornelia Huck (cohuck@redhat.com) wrote: > > > > On Tue, 5 Jan 2021 12:41:25 -0800 > > > > Ram Pai wrote: > > > > > > > > > On Tue, Jan 05, 2021 at 11:56:14AM +0100, Halil Pasic wrote: > > > > > > On Mon, 4 Jan 2021 10:40:26 -0800 > > > > > > Ram Pai wrote: > > > > > > > > > > > The main difference between my proposal and the other proposal is... > > > > > > > > > > > > > > In my proposal the guest makes the compatibility decision and acts > > > > > > > accordingly. In the other proposal QEMU makes the compatibility > > > > > > > decision and acts accordingly. I argue that QEMU cannot make a good > > > > > > > compatibility decision, because it wont know in advance, if the guest > > > > > > > will or will-not switch-to-secure. > > > > > > > > > > > > > > > > > > > You have a point there when you say that QEMU does not know in advance, > > > > > > if the guest will or will-not switch-to-secure. I made that argument > > > > > > regarding VIRTIO_F_ACCESS_PLATFORM (iommu_platform) myself. My idea > > > > > > was to flip that property on demand when the conversion occurs. David > > > > > > explained to me that this is not possible for ppc, and that having the > > > > > > "securable-guest-memory" property (or whatever the name will be) > > > > > > specified is a strong indication, that the VM is intended to be used as > > > > > > a secure VM (thus it is OK to hurt the case where the guest does not > > > > > > try to transition). That argument applies here as well. > > > > > > > > > > As suggested by Cornelia Huck, what if QEMU disabled the > > > > > "securable-guest-memory" property if 'must-support-migrate' is enabled? > > > > > Offcourse; this has to be done with a big fat warning stating > > > > > "secure-guest-memory" feature is disabled on the machine. > > > > > Doing so, will continue to support guest that do not try to transition. > > > > > Guest that try to transition will fail and terminate themselves. > > > > > > > > Just to recap the s390x situation: > > > > > > > > - We currently offer a cpu feature that indicates secure execution to > > > > be available to the guest if the host supports it. > > > > - When we introduce the secure object, we still need to support > > > > previous configurations and continue to offer the cpu feature, even > > > > if the secure object is not specified. > > > > - As migration is currently not supported for secured guests, we add a > > > > blocker once the guest actually transitions. That means that > > > > transition fails if --only-migratable was specified on the command > > > > line. (Guests not transitioning will obviously not notice anything.) > > > > - With the secure object, we will already fail starting QEMU if > > > > --only-migratable was specified. > > > > > > > > My suggestion is now that we don't even offer the cpu feature if > > > > --only-migratable has been specified. For a guest that does not want to > > > > transition to secure mode, nothing changes; a guest that wants to > > > > transition to secure mode will notice that the feature is not available > > > > and fail appropriately (or ultimately, when the ultravisor call fails). > > > > We'd still fail starting QEMU for the secure object + --only-migratable > > > > combination. > > > > > > > > Does that make sense? > > > > > > It's a little unusual; I don't think we have any other cases where > > > --only-migratable changes the behaviour; I think it normally only stops > > > you doing something that would have made it unmigratable or causes > > > an operation that would make it unmigratable to fail. > > > > I agree, --only-migratable is supposed to be a *behavioural* toggle > > for QEMU. It must /not/ have any impact on the guest ABI. > > > > A management application needs to be able to add/remove --only-migratable > > at will without changing the exposing guest ABI. > > At the qemu level, it sounds like the right thing to do is to fail > outright if all of the below are true: > 1. --only-migratable is specified > 2. -cpu host is specified > 3. unpack isn't explicitly disabled > 4. the host CPU actually does have the unpack facility > > That can be changed if & when migration support is added for PV. That sounds right to me. Dave > > -- > 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 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK