The kpatch kernel patching solution uses the livepatch kernel subsystem to redirect outdated functions to updated ones.

Applying a live kernel patch to a system triggers the following processes:

1. The kernel patch module is copied to the /var/lib/kpatch/ directory and registered for re-application to the kernel by systemd on next boot.
2. The kpatch module loads into the running kernel and the new functions are registered to the ftrace mechanism with a pointer to the location in memory of the new code.

When the kernel accesses the patched function, the ftrace mechanism redirects it, bypassing the original functions and leading the kernel to the patched version of the function.