Hi, first of all thanks for sharing a nice extra use case. A few comments: "Given that postcopy migration doesn't copy all the guest RAM upfront, we can migrate the VM from one instance to another with practically zero downtime. So we can use postcopy migration within the same host to dynamically update the QEMU thus achieving QEMU hot-patching. Pre requisites"
Zero "full-stop" downtime that is true, but please if you e.g. announce/advertise this to anybody make it clear that the guest will have through a phase of long-latency page-faults. That is not that long on a local system, but still perceivable in the guest - so it is great, but not a 100% free hot-patch. "Support for postcopy migration isn't present in libvirt yet. Even when it is supported, libvirt doesn't support the notion of VM migration within the same host. Some development effort in addition to just postcopy migration is needed in libvirt to support hot-patching." Yes, I agree given an official support in Libvirt this might be a nice and fast local update. Once that is done upstream in libvirt I'd absolutely love to test/exploit this. Until then let me share a trick how you can achieve this today via a smart setup - you might use that for your tests while working on this. You can drive KVM from a LXD container basics are at [1] and a full test/dev example can be [2]. With that set up you can on a single host migrate from old/new qemu, but even more than that you can exchange effectively everything except the kernel which is shared by the containers. Eventually an implementation in libvirt is much better, but I thought until then this might help you. [1]: https://insights.ubuntu.com/2016/03/22/lxd-2-0-your-first-lxd-container/ [2]: http://paste.ubuntu.com/24622647/ -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1692457 Title: [17.10 FEAT] libvirt: libvirt support for QEMU live patching To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-power-systems/+bug/1692457/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
