Google’s LUO (Live Update Orchestrator) subsystem, aimed at updating the Linux kernel in Live mode without a physical reboot, has been accepted into the Linux kernel codebase for release 6.19. The LUO subsystem is based on the KHO (Kexec HandOver) mechanism, which was previously added to the 6.16 kernel. This mechanism allows for the launch of a new kernel from an old one without losing the system state.
The Live Update Orchestrator enables a full reboot and kernel update without interrupting work or losing the system, device, and process states. In addition to the KHO functionality, the LUO subsystem preserves device and RAM state and ensures the continuity of DMA and interrupt handling operations. This state is maintained until the switch to the new kernel, and it is restored after the new kernel is enabled without disrupting ongoing device operations carried out by the system and applications in user space.
The new series of patches includes a feature that allows for saving memfd file descriptors to maintain the state of essential data in memory between reboots, such as the contents of the RAM of virtual machines. This technology is particularly beneficial for quickly updating servers with virtualization systems based on the KVM hypervisor to address security and stability issues with minimal downtime for virtual machines. Google has already implemented this technology in its work environments.