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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id e18sm32260645wrx.50.2020.09.16.06.17.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Sep 2020 06:17:01 -0700 (PDT) From: Vitaly Kuznetsov To: Paolo Bonzini Subject: Re: [BUG] Migration hv_time rollback In-Reply-To: <37b1b2b7-40f5-d0b1-2709-df9fe24fc65f@redhat.com> References: <20200916090602.blkm7eym6g5bnvvk@tartarus> <20200916112956.GE2833@work-vm> <37b1b2b7-40f5-d0b1-2709-df9fe24fc65f@redhat.com> Date: Wed, 16 Sep 2020 15:17:00 +0200 Message-ID: <87363hj1yr.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: 0.002 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 = 2020/09/16 02:16:02 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -50 X-Spam_score: -5.1 X-Spam_bar: ----- X-Spam_report: (-5.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.999, 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: Marcelo Tosatti , Juan Quintela , "Michael S. Tsirkin" , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Antoine Damhet Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Paolo Bonzini writes: > On 16/09/20 13:29, Dr. David Alan Gilbert wrote: >>> I have tracked the bug to the fact that `kvmclock` is not exposed and >>> disabled from qemu PoV but is in fact used by `hv-time` (in KVM). >>> >>> I think we should enable the `kvmclock` (qemu device) if `hv-time` is >>> present and add Hyper-V support for the `kvmclock_current_nsec` >>> function. > > Yes, this seems correct. I would have to check but it may even be > better to _always_ send kvmclock data in the live migration stream. > The question I have is: with 'kvm=off', do we actually restore TSC reading on migration? (and I guess the answer is 'no' or Hyper-V TSC page would 'just work' I guess). So yea, maybe dropping the 'cpu->env.features[FEAT_KVM]' check is the right fix. -- Vitaly