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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 B3B65C433DB for ; Fri, 15 Jan 2021 00:21:43 +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 0726623A9D for ; Fri, 15 Jan 2021 00:21:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0726623A9D 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]:51716 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l0Cs1-0000sK-Qo for qemu-devel@archiver.kernel.org; Thu, 14 Jan 2021 19:21:41 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48200) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l0Cq4-00004t-F5; Thu, 14 Jan 2021 19:19:40 -0500 Received: from bilbo.ozlabs.org ([203.11.71.1]:55607 helo=ozlabs.org) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l0Cq1-0003Pv-1F; Thu, 14 Jan 2021 19:19:40 -0500 Received: by ozlabs.org (Postfix, from userid 1007) id 4DH1yV5Pblz9sSs; Fri, 15 Jan 2021 11:19:30 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gibson.dropbear.id.au; s=201602; t=1610669970; bh=wcy9LPpFUMZ9gzA/ytL/D68EWk8OlzQliGIpe+KcrvE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=L2zdbUE0G9bDudtydYhL64mVS+oPklq4KR7l0GUTv8rSKW4urpLoiYYA5wjnddvpM Qpedk98R8mTt5UGfRy+nS6+R2DxyUvX0xAji7dKGB/rzmJm25IAzE6/TlvwaGahm6i lQwiEzD4noPcNATzCUqtb2txCxG7c7MmIv5DNY+0= Date: Fri, 15 Jan 2021 10:51:25 +1100 From: David Gibson To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [for-6.0 v5 11/13] spapr: PEF: prevent migration Message-ID: <20210114235125.GO435587@yekko.fritz.box> References: <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> <20210114112517.GE1643043@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="MmQIYbZiCoQ2kDro" Content-Disposition: inline In-Reply-To: <20210114112517.GE1643043@redhat.com> Received-SPF: pass client-ip=203.11.71.1; envelope-from=dgibson@ozlabs.org; helo=ozlabs.org X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.248, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action 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: pair@us.ibm.com, Cornelia Huck , 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 , "Dr. David Alan Gilbert" , Greg Kurz , qemu-s390x@nongnu.org, rth@twiddle.net, Marcelo Tosatti , qemu-ppc@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --MmQIYbZiCoQ2kDro Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jan 14, 2021 at 11:25:17AM +0000, Daniel P. Berrang=E9 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: > > >=20 > > > > 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: > > >=20 > > > > > > The main difference between my proposal and the other proposal = is... > > > > > >=20 > > > > > > In my proposal the guest makes the compatibility decision and= acts > > > > > > accordingly. In the other proposal QEMU makes the compatibil= ity > > > > > > decision and acts accordingly. I argue that QEMU cannot make = a good > > > > > > compatibility decision, because it wont know in advance, if t= he guest > > > > > > will or will-not switch-to-secure. > > > > > > =20 > > > > >=20 > > > > > You have a point there when you say that QEMU does not know in ad= vance, > > > > > if the guest will or will-not switch-to-secure. I made that argum= ent > > > > > regarding VIRTIO_F_ACCESS_PLATFORM (iommu_platform) myself. My id= ea > > > > > was to flip that property on demand when the conversion occurs. D= avid > > > > > explained to me that this is not possible for ppc, and that havin= g the > > > > > "securable-guest-memory" property (or whatever the name will be) > > > > > specified is a strong indication, that the VM is intended to be u= sed 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. =20 > > > >=20 > > > > As suggested by Cornelia Huck, what if QEMU disabled the > > > > "securable-guest-memory" property if 'must-support-migrate' is enab= led? > > > > 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 transit= ion. > > > > Guest that try to transition will fail and terminate themselves. > > >=20 > > > Just to recap the s390x situation: > > >=20 > > > - 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. > > >=20 > > > 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 availab= le > > > and fail appropriately (or ultimately, when the ultravisor call fails= ). > > > We'd still fail starting QEMU for the secure object + --only-migratab= le > > > combination. > > >=20 > > > Does that make sense? > >=20 > > 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. >=20 > I agree, --only-migratable is supposed to be a *behavioural* toggle > for QEMU. It must /not/ have any impact on the guest ABI. >=20 > 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. --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. 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