Engineers from Google have published a set of patches for discussion among Linux kernel developers, implementing the Live Update Orchestrator (LUO) subsystem, which is intended for core updates in live mode. Unlike mechanisms like livepatch, Ksplice, kpatch, and kGraft, the new system is not limited to applying individual fixes to the running Linux kernel, but allows for a full reboot and update of the kernel without stopping the operation of individual devices. The project is based on a set of KHO (Kexec HandOver) patches to the kexec mechanism used to load a new kernel from an already running Linux kernel without a physical reboot.
The primary area of application for LUO is cloud environments, where it will become possible to update the KVM hypervisor without interrupting running of virtual machinesSpecifically, it will be possible to pause virtual machines during the kernel reboot with the hypervisor, keeping all devices attached to the virtual machines in a working state.
To realize this capability, LUO provides mechanisms for preserving the state of devices before switching to the new kernel and restoring the state immediately after engaging the new kernel, such that the continuous operations of the system and applications in user space with the devices will not be disrupted. During the kernel reboot, continuity of operations associated with DMA and interrupt handling is also ensured.
To coordinate state preservation and switching to the new kernel, LUO provides an API that allows other kernel subsystems to attach handlers to monitor and participate in the live reboot process. Among the subsystems that can integrate with LUO are the KVM hypervisor, iommu, the interrupt system, and drivers. KHO (Kexec HandOver) is used to transfer the state of memory from the old kernel to the new one. Management is done through sysfs files '/sys/kernel/liveupdate/{state, prepare, finish}'.
Source: opennet.ru
