self doubt.

Question

who is responsible for changing the mode bit of the system. Is it the privileged or the non-privileged instruction? some authors are writing that it can be privileged or non-privileged instruction if it is non-privileged instruction then a process running in user mode can change the mode bit and execute in kernel mode even though it should not be running in kernel mode? so in conclusion what is needed to shift from kernel mode to user mode?

Answer 1

Interrupt is generated to change mode from User and Kernel mode thus it's Privileged instruction and obviously process is currently in user mode before asking to switch to kernel mode.