Moving into or out of a control register, such as to enable a processor feature. Disabling or enabling interrupts. Reading or writing model-specific registers.

Moving into or out of a control register, such as to enable a processor feature. Disabling or enabling interrupts. Reading or writing model-specific registers. Saving registers, switching stacks, and calling another function, then switching back and restoring registers when the function returns. Initializing and using hardware virtualization features (e.g. Intel VT). Using features like SMAP (preventing accidental access from the kernel to user memory through a wild pointer, temporary enabling it in careful dedicated routines like copy_from_user and copy_to_user). Making raw system calls from userspace.