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Tsirkin" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH] vhost-vsock: fix migration issue when seqpacket is supported Message-ID: <20210909044603-mutt-send-email-mst@kernel.org> References: <20210907124935.147164-1-sgarzare@redhat.com> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.393, 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_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: Eduardo Habkost , Jiang Wang , qemu-stable@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi , Arseny Krasnov , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Sep 07, 2021 at 02:22:24PM +0100, Daniel P. Berrangé wrote: > On Tue, Sep 07, 2021 at 02:49:35PM +0200, Stefano Garzarella wrote: > > Commit 1e08fd0a46 ("vhost-vsock: SOCK_SEQPACKET feature bit support") > > enabled the SEQPACKET feature bit. > > This commit is released with QEMU 6.1, so if we try to migrate a VM where > > the host kernel supports SEQPACKET but machine type version is less than > > 6.1, we get the following errors: > > > > Features 0x130000002 unsupported. Allowed features: 0x179000000 > > Failed to load virtio-vhost_vsock:virtio > > error while loading state for instance 0x0 of device '0000:00:05.0/virtio-vhost_vsock' > > load of migration failed: Operation not permitted > > > > Let's disable the feature bit for machine types < 6.1, adding a > > `features` field to VHostVSock to simplify the handling of upcoming > > features we will support. > > IIUC, this will still leave migration broken for anyone migrating > a >= 6.1 machine type between a kernel that supports SEQPACKET and > a kernel lacking that, or vica-verca. > > If a feature is dependant on a host kernel feature we can't turn > that on automatically as part of the machine type, as we need > ABI stability across migration indepdant of kernel version. > > > Regards, > Daniel This is a fundamental problem we have with kernel accelerators. A higher level solution at management level is needed. For now yes, we do turn features on by default, consistent kernels on source and destination are assumed. For downstreams not a problem at all as they update userspace and kernel in concert. > -- > |: 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 :|