Linux 5.5 Kernel Livepatching To Allow Tracking System State

It's been a while since last having any new features to report on in regards to the Linux kernel's livepatching infrastructure for applying kernel updates without system reboots. With the Linux 5.5 there is a big addition to livepatching and that is support for tracking the system state changes.

Linux 5.5 will bring a new system state API to the livepatching infrastructure. Currently Linux livepatching with the atomic replace / cumulative patches functionality can remove previously applied fixes and other quite versatile support, but when the system state is altered is when future live-patches can go awry.

In particular, patches touching shadow variables and callbacks might be altered in such a way that it's no longer viable to remove those live-patches or jumping back to the original kernel code. With the live-patching system state tracking, it can archive the data to manipulate and restore the system state in order to revert patches. The API also allows for defining compatibility between live-patches.

The new documentation to be added with Linux 5.5 explains the live-patching system state tracking in more detail.

This system state support was led by SUSE's Petr Mladek. Currently that support is housed in for-5.5/system-state ahead of the Linux 5.5 merge window opening later this month.