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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id n10sm5389452wmk.7.2020.09.22.08.19.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2020 08:19:03 -0700 (PDT) From: Vitaly Kuznetsov To: "Dr. David Alan Gilbert" , Antoine Damhet Subject: Re: [PATCH] target/i386: always create kvmclock device In-Reply-To: <20200918152656.GN2816@work-vm> References: <20200917111306.819263-1-vkuznets@redhat.com> <20200917122559.e7i5o64k7rw7urdh@tartarus> <87ft7gh6gy.fsf@vitty.brq.redhat.com> <20200917144237.GK2793@work-vm> <875z8ch2m6.fsf@vitty.brq.redhat.com> <20200917174410.GU2793@work-vm> <20200918151213.x2dntgytybh7dkmx@tartarus> <20200918152656.GN2816@work-vm> Date: Tue, 22 Sep 2020 17:19:02 +0200 Message-ID: <87y2l1et5l.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vkuznets@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/22 00:31:51 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.455, 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_H5=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Marcelo Tosatti , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" "Dr. David Alan Gilbert" writes: > * Antoine Damhet (antoine.damhet@blade-group.com) wrote: >> On Thu, Sep 17, 2020 at 06:44:10PM +0100, Dr. David Alan Gilbert wrote: >> >> [...] >> >> > > >> > >> > > >> > Shouldn't the old check used when machine type <= 5.1 in order to avoid >> > > >> > migration incompatibility ? >> > > >> >> > > >> Hm, when the check fails we just don't create the device and no error is >> > > >> reported, so even if we have kvmclock data in the migration stream but >> > > >> fail to create it migration will still succeed, right? (not a migration >> > > >> expert here :-) >> > > > >> > > > When the migration stream is parsed, it'll try and find a "kvmclock" >> > > > device to pass the data it's reading to; if one doesn't exist it'll >> > > > fail. >> > > >> > > This may happen with an older machine type when the destination is >> > > running an unfixed QEMU and the source has the fix, right? >> > >> > Yes I think so. >> > >> > > The solution >> > > would be to introduce a flag for older machine types (or for new ones) >> > > like 'kvmclock_always'. >> > >> > Yep sounds the normal answer. >> > (You might want to try it first to trigger the bug) >> >> So, I tried the patch and: >> >> # patched -> patched >> >> Everything working as expected >> >> # patched -> unpatched >> >> Migration failure with: >> >> ``` >> Unknown savevm section or instance 'kvmclock' 0. Make sure that your current VM setup matches your saved VM setup, including any hotplugged devices >> load of migration failed: Invalid argument >> ``` > > Right, that's what I expected and said we need to wire this fix to the > machine type. > v2 with the idea implemented is coming. As I'm not a regular contributor to machine types, please review thoroughly :-) -- Vitaly