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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id z23-20020a170906435700b006b0e62bee84sm13171177ejm.115.2022.04.12.05.48.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Apr 2022 05:48:20 -0700 (PDT) From: Vitaly Kuznetsov To: Divya Garg Subject: Re: [Qemu-devel] [PATCH 6/8] i386/kvm: hv-stimer requires hv-time and hv-synic In-Reply-To: <2dde6caa-8d02-7022-d2c2-aa56c408f5f2@nutanix.com> References: <2dde6caa-8d02-7022-d2c2-aa56c408f5f2@nutanix.com> Date: Tue, 12 Apr 2022 14:48:20 +0200 Message-ID: <87tuay5uy3.fsf@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=170.10.129.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Divya Garg writes: > Hi Vitaly Kuznetsov ! > I was working on hyperv flags and saw that we introduced new > dependencies some > time back > (https://sourcegraph.com/github.com/qemu/qemu/-/commit/c686193072a47032d83cb4e131dc49ae30f9e5d7?visible=1). > After these changes, if we try to live migrate a vm from older qemu to newer > one having these changes, it fails showing dependency issue. > > I was wondering if this is the expected behaviour or if there is any work > around for handing it ? Or something needs to be done to ensure backward > compatibility ? Hi Divya, configurations with 'hv-stimer' and without 'hv-synic'/'hv-time' were always incorrect as Windows can't use the feature, that's why the dependencies were added. It is true that it doesn't seem to be possible to forward-migrate such VMs to newer QEMU versions. We could've tied these new dependencies to newer machine types I guess (so old machine types would not fail to start) but we didn't do that back in 4.1 and it's been awhile since... Not sure whether it would make much sense to introduce something for pre-4.1 machine types now. Out of curiosity, why do such "incorrect" configurations exist? Can you just update them to include missing flags on older QEMU so they migrate to newer ones without issues? -- Vitaly