Answer / neo

There are 2 situations when Linux can switch from user Space
to Kernel Space:-

1) by doing System calls
2) When interrupt comes (to handle interrupt)

Linux can switch from kernel Space to User space:-
1) process in kernel mode is preempted.
2) After completion of Interrupt handler / System call

Answer / softy

There are 2 situations when Linux can switch from user Space
to Kernel Space:-

1) by doing System calls
2) When interrupt comes (to handle interrupt)
3) by executing 128 (0x80 ) instruction or doing sysenter

Linux can switch from kernel Space to User space:-
1) process in kernel mode is preempted.
2) After completion of Interrupt handler / System call
3) performing sysexit sys call

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