Switch from User Space to Kernel Space

Question

What are the distinct ways the Linux can switch from User Space to Kernel Space & vice-versa?

Answer 1

There are two situations while Linux can switch from user Space to Kernel Space:-

a)      by doing System calls

b)      While interrupt comes (to handle interrupt)

c)      By executing 128 (0x80 ) instruction or doing sysenter

Linux can switch through kernel Space to User space:-

a.      process in kernel mode is preempted.

b.      After completion of Interrupt handler / System call

c.      Performing sys exit sys call