Wikipedia
kGraft is a feature of the Linux kernel that implements live patching of a running kernel, which allows kernel patches to be applied while the kernel is still running. By avoiding the need for rebooting the system with a new kernel that contains the desired patches, kGraft aims to maximize the system uptime and availability. At the same time, kGraft allows kernel-related security updates to be applied without deferring them to scheduled downtimes. Internally, kGraft allows entire functions in a running kernel to be replaced with their patched versions, doing that safely by selectively using original versions of functions to ensure per- process consistency while the live patching is performed.
kGraft is developed by SUSE, with its source code licensed under the terms of versions two and three of the GNU General Public License (GPL). In April 2014, kGraft was submitted for inclusion into the Linux kernel mainline, and the minimalistic foundations for live patching were merged into the Linux kernel mainline in kernel version 4.0, which was released on April 12, 2015.