Google engineers for the past number of months have been working on the Live Update Orchestrator as a new way of applying live Linux kernel updates. The Live Update Orchestrator "LUO" builds atop the Kexec Handover "KHO" functionality already within the kernel. Google has since been deplyoing LUO in their production environments for faster security updates to kernels, especially when involving VMs. LUO is now upstream in Linux 6.19.

Merged to the Git tree this weekend for Linux 6.19 were the non-MM updates sent in by Andrew Morton. Most notable with that pull was the prep work and ultimately landing the Live Update Orchestrator code. Here’s how this live update functionality is officially described:

"This series introduces the Live Update Orchestrator, a kernel subsystem designed to facilitate live kernel updates using a kexec-based reboot. This capability is critical for cloud environments, allowing hypervisors to be updated with minimal downtime for running virtual machines. LUO achieves this by preserving the state of selected resources, such as memory, devices and their dependencies, across the kernel transition.

As a key feature, this series includes support for preserving memfd file descriptors, which allows critical in-memory data, such as guest RAM or any other large memory region, to be maintained in RAM across the kexec reboot."

Simply put, keeping more resources active for speeding up switching to a new kernel via Kexec Handover.