This parameter can be used to control the NMI watchdog (i.e. the hard lockup detector) on x86 systems.
The hard lockup detector monitors each CPU for its ability to respond to timer interrupts. The mechanism utilizes CPU performance counter registers that are programmed to generate Non-Maskable Interrupts (NMIs) periodically while a CPU is busy. Hence, the alternative name ‘NMI watchdog’.
The NMI watchdog is disabled by default if the kernel is running as a guest in a KVM virtual machine. This default can be overridden by adding
to the guest kernel command line (see Documentation/admin-guide/kernel-parameters.rst).source