Hy-FiX: Fast In-Place Upgrades of KVM Hypervisors

Maintaining up-to-date KVM hypervisors requires regular upgrades to the host kernel, hence rebooting the physical host with the consequent termination of running Virtual Machines (VMs). Cloud platforms capable of massive large-scale live migrations evacuate VMs from the hosts before rebooting, minimizing the impact over VM up-time. However, scenarios exist where resource constraints make live migration undesirable, or the presence of fault-tolerant instances (e.g., replicated services) favors the adoption of VM termination, a simpler but more disruptive strategy. In this article, we present Hy-FiX, a fast in-place upgrade solution for KVM hypervisors. Hy-FiX preserves VM memory across host reboots, protecting the execution state of running guests while hypervisor upgrades are applied. Hy-FiX memory preservation across reboot, combined with a mixed suspend-to-disk/suspend-to-RAM technique, achieves a 2.31-second checkpoint/restore time for a 256 GB VM, and Hy-FiX lazy memory initialization reboots an enterprise-class host in constant time (7.6 seconds) regardless of its equipped memory. Hy-FiX is, therefore, a better alternative to classical VM termination and restart.