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[81.97.203.96]) by smtp.gmail.com with ESMTPSA id y7-20020a5d4707000000b00291f1a5ced6sm8980045wrq.53.2023.01.09.09.52.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Jan 2023 09:52:24 -0800 (PST) Date: Mon, 9 Jan 2023 17:52:22 +0000 From: "Dr. David Alan Gilbert" To: James Bottomley Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Stefan Berger , qemu-devel@nongnu.org, Markus Armbruster Subject: Re: [PATCH 2/2] tpm: add backend for mssim Message-ID: References: <9fac7d95-d891-413f-93f1-18324c7943ea@linux.ibm.com> <29e99f54-d5e8-b18d-08a6-d24435032272@linux.ibm.com> <5c07f6ab6adfe53f7e7fbeeda67f2eb62afccdfa.camel@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5c07f6ab6adfe53f7e7fbeeda67f2eb62afccdfa.camel@linux.ibm.com> User-Agent: Mutt/2.2.9 (2022-11-12) Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org * James Bottomley (jejb@linux.ibm.com) wrote: > On Mon, 2023-01-09 at 16:59 +0000, Dr. David Alan Gilbert wrote: > > * Daniel P. Berrangé (berrange@redhat.com) wrote: > > > On Fri, Dec 16, 2022 at 08:32:44AM -0500, Stefan Berger wrote: > [...] > > > > I do see it because the *volatile state* cannot be extracted from > > > > this device. The state of the PCRs is going to be lost. > > > > > > All the objections you're raising are related to the current > > > specifics of the implementation of the mssim remote server. > > > While valid, this is of no concern to QEMU when deciding whether > > > to require a migration blocker on the client side. This is 3rd > > > party remote service that should be considered a black box from > > > QEMU's POV. It is possible to write a remote server that supports > > > the mssim network protocol, and has the ability to serialize > > > its state. Whether such an impl exists today or not is separate. > > > > We would normally want an example of a working implementation though > > wouldn't we? > > > > So I think it's fair to at least want some documentation; if it can > > be documented and works, fine; if it doesn't work, then it needs a > > blocker. > > It works under limited circumstances ... in fact similar circumstances > passthrough migration works under, Well, not that similar - people expect passthrough migration to fail because, being nailed to a physical servers hardware it's not likely to migrate; where as you're creating a new virtual thing which people might imagine is similar to the existing swtpm. Their imagination might be wrong and thus you need to say why. > which is also not documented. The Inductive proof that we should have no good documentation doesn't get us anywhere. > external MSSIM TPM emulator has to be kept running to preserve the > state. If you restart it, the migration will fail. Document that and we're getting there. Dave > James > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK