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Fri, 26 Jun 2020 09:33:00 +0000 (UTC) Date: Fri, 26 Jun 2020 10:32:57 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Janosch Frank Subject: Re: [PATCH v3 0/9] Generalize memory encryption models Message-ID: <20200626093257.GC1028934@redhat.com> References: <20200619114526.6a6f70c6.cohuck@redhat.com> <79890826-f67c-2228-e98d-25d2168be3da@redhat.com> <20200619120530.256c36cb.cohuck@redhat.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.14.0 (2020-05-02) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Received-SPF: pass client-ip=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/26 01:49:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: 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, dgilbert@redhat.com, pasic@linux.ibm.com, Christian Borntraeger , qemu-s390x@nongnu.org, qemu-ppc@nongnu.org, pbonzini@redhat.com, Richard Henderson , mdroth@linux.vnet.ibm.com, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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. 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 :|