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=-7.5 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 9C088C433E0 for ; Thu, 14 Jan 2021 11:27:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D71623A34 for ; Thu, 14 Jan 2021 11:27:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726770AbhANL1F (ORCPT ); Thu, 14 Jan 2021 06:27:05 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:41785 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726672AbhANL1E (ORCPT ); Thu, 14 Jan 2021 06:27:04 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610623537; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=XqOfTnB39liRcHVwSunn3UeUAIK7R5nO1WAUm9BBMfY=; b=HddOSACmGqDVCQVKB4J8tG7+hBfBCkHKNAkKFUAhipA+0XTDrMGUaQzBo1PDyvd645T1yE P1yNktO+g6ft9tZ07z5u1NyssV1+21eBmX8SnKh6KTAOgaGEYEn3xQfJ+fU9MhdJdXGqaS oboQWTgAhdYGvtUdNsIWU6RNAWvxr2U= 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-228-en6P0JmrP52Xg9Ljg_P9hg-1; Thu, 14 Jan 2021 06:25:34 -0500 X-MC-Unique: en6P0JmrP52Xg9Ljg_P9hg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A4E27806663; Thu, 14 Jan 2021 11:25:31 +0000 (UTC) Received: from redhat.com (ovpn-115-77.ams2.redhat.com [10.36.115.77]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 062885B6AD; Thu, 14 Jan 2021 11:25:20 +0000 (UTC) Date: Thu, 14 Jan 2021 11:25:17 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Cc: 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, David Gibson , 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: <20210114112517.GE1643043@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20201217123842.51063918.cohuck@redhat.com> <20201217151530.54431f0e@bahia.lan> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210113124226.GH2938@work-vm> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|