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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" Subject: Re: [PATCH v3 0/9] Generalize memory encryption models Message-ID: <20200626105846.GF1028934@redhat.com> 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 Received-SPF: pass client-ip=205.139.110.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/26 01:55:55 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, brijesh.singh@amd.com, Janosch Frank , kvm@vger.kernel.org, David Hildenbrand , Cornelia Huck , qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com, pasic@linux.ibm.com, Christian Borntraeger , qemu-s390x@nongnu.org, mst@redhat.com, David Gibson , pbonzini@redhat.com, qemu-ppc@nongnu.org, Richard Henderson , Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 :|