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=-2.6 required=3.0 tests=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 F3E9FC433DF for ; Fri, 26 Jun 2020 10:59:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C7095206DD for ; Fri, 26 Jun 2020 10:59:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RaT35qUf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728232AbgFZK7X (ORCPT ); Fri, 26 Jun 2020 06:59:23 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:23817 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728161AbgFZK7X (ORCPT ); Fri, 26 Jun 2020 06:59:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593169160; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HoikqKLRzwRdXXNNoEwPoeKQEfoqUSwR6yN/kfA4ulg=; b=RaT35qUfbyTOZbsolVNztw+Y+eOhZx5qL3I5unHAj3oSxds305ytgyezPz8i4ll2OdUYn8 gBPM9ZS3fwHzL/TVao3v5gs9PVXWmasgaecZS0SuQr/j6us52seYwpWvDDVKEl73irFYL0 lyKYP9wRj4yHByHKJpJkOsH8qjilfGE= 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-440-VkptwSgrO7K1UmdVZVQlNQ-1; Fri, 26 Jun 2020 06:59:02 -0400 X-MC-Unique: VkptwSgrO7K1UmdVZVQlNQ-1 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 6F555804002; Fri, 26 Jun 2020 10:59:00 +0000 (UTC) Received: from redhat.com (unknown [10.36.110.51]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A6D955D9CA; Fri, 26 Jun 2020 10:58:49 +0000 (UTC) Date: Fri, 26 Jun 2020 11:58:46 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Cc: Janosch Frank , pair@us.ibm.com, Cornelia Huck , brijesh.singh@amd.com, Eduardo Habkost , kvm@vger.kernel.org, David Hildenbrand , mst@redhat.com, qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com, pasic@linux.ibm.com, Christian Borntraeger , qemu-s390x@nongnu.org, qemu-ppc@nongnu.org, pbonzini@redhat.com, Richard Henderson , David Gibson Subject: Re: [PATCH v3 0/9] Generalize memory encryption models Message-ID: <20200626105846.GF1028934@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <358d48e5-4c57-808b-50da-275f5e2a352c@redhat.com> <20200622140254.0dbe5d8c.cohuck@redhat.com> <20200625052518.GD172395@umbus.fritz.box> <025fb54b-60b7-a58b-e3d7-1bbaad152c5c@redhat.com> <20200626044259.GK172395@umbus.fritz.box> <892533f8-cd3c-e282-58c2-4212eb3a84b8@redhat.com> <20200626093257.GC1028934@redhat.com> <558e8978-01ba-d8e8-9986-15efbbcbca96@linux.ibm.com> <20200626102903.GD3087@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200626102903.GD3087@work-vm> User-Agent: Mutt/1.14.0 (2020-05-02) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Jun 26, 2020 at 11:29:03AM +0100, Dr. David Alan Gilbert wrote: > * Janosch Frank (frankja@linux.ibm.com) wrote: > > On 6/26/20 11:32 AM, Daniel P. Berrangé wrote: > > > On Fri, Jun 26, 2020 at 11:01:58AM +0200, Janosch Frank wrote: > > >> On 6/26/20 8:53 AM, David Hildenbrand wrote: > > >>>>>>> Does this have any implications when probing with the 'none' machine? > > >>>>>> > > >>>>>> I'm not sure. In your case, I guess the cpu bit would still show up > > >>>>>> as before, so it would tell you base feature availability, but not > > >>>>>> whether you can use the new configuration option. > > >>>>>> > > >>>>>> Since the HTL option is generic, you could still set it on the "none" > > >>>>>> machine, though it wouldn't really have any effect. That is, if you > > >>>>>> could create a suitable object to point it at, which would depend on > > >>>>>> ... details. > > >>>>>> > > >>>>> > > >>>>> The important point is that we never want the (expanded) host cpu model > > >>>>> look different when either specifying or not specifying the HTL > > >>>>> property. > > >>>> > > >>>> Ah, yes, I see your point. So my current suggestion will satisfy > > >>>> that, basically it is: > > >>>> > > >>>> cpu has unpack (inc. by default) && htl specified > > >>>> => works (allowing secure), as expected > > >>> > > >>> ack > > >>> > > >>>> > > >>>> !cpu has unpack && htl specified > > >>>> => bails out with an error > > >>> > > >>> ack > > >>> > > >>>> > > >>>> !cpu has unpack && !htl specified > > >>>> => works for a non-secure guest, as expected > > >>>> => guest will fail if it attempts to go secure > > >>> > > >>> ack, behavior just like running on older hw without unpack > > >>> > > >>>> > > >>>> cpu has unpack && !htl specified > > >>>> => works as expected for a non-secure guest (unpack feature is > > >>>> present, but unused) > > >>>> => secure guest may work "by accident", but only if all virtio > > >>>> properties have the right values, which is the user's > > >>>> problem > > >>>> > > >>>> That last case is kinda ugly, but I think it's tolerable. > > >>> > > >>> Right, we must not affect non-secure guests, and existing secure setups > > >>> (e.g., older qemu machines). Will have to think about this some more, > > >>> but does not sound too crazy. > > >> > > >> I severely dislike having to specify things to make PV work. > > >> The IOMMU is already a thorn in our side and we're working on making the > > >> whole ordeal completely transparent so the only requirement to make this > > >> work is the right machine, kernel, qemu and kernel cmd line option > > >> "prot_virt=1". That's why we do the reboot into PV mode in the first place. > > >> > > >> I.e. the goal is that if customers convert compatible guests into > > >> protected ones and start them up on a z15 on a distro with PV support > > >> they can just use the guest without having to change XML or command line > > >> parameters. > > > > > > If you're exposing new features to the guest machine, then it is usually > > > to be expected that XML and QEMU command line will change. Some simple > > > things might be hidable behind a new QEMU machine type or CPU model, but > > > there's a limit to how much should be hidden that way while staying sane. > > > > > > I'd really expect the configuration to change when switching a guest to > > > a new hardware platform and wanting major new functionality to be enabled. > > > The XML / QEMU config is a low level instantiation of a particular feature > > > set, optimized for a specific machine, rather than a high level description > > > of ideal "best" config independent of host machine. > > > > You still have to set the host command line and make sure that unpack is > > available. Currently you also have to specify the IOMMU which we like to > > drop as a requirement. Everything else is dependent on runtime > > information which tells us if we need to take a PV or non-PV branch. > > Having the unpack facility should be enough to use the unpack facility. > > > > Keep in mind that we have no real concept of a special protected VM to > > begin with. If the VM never boots into a protected kernel it will never > > be protected. On a reboot it drops from protected into unprotected mode > > to execute the bios and boot loader and then may or may not move back > > into a protected state. > > My worry isn't actually how painful adding all the iommu glue is, but > what happens when users forget; especially if they forget for one > device. > > I could appreciate having a machine option to cause iommu to then get > turned on with all other devices; but I think also we could do with > something that failed with a nice error if an iommu flag was missing. > For SEV this could be done pretty early, but for power/s390 I guess > you'd have to do this when someone tried to enable secure mode, but > I'm not sure you can tell. What is the cost / downside of turning on the iommu option for virtio devices ? Is it something that is reasonable for a mgmt app todo unconditionally, regardless of whether memory encryption is in use, or will that have a negative impact on things ? 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 :|