A page fault happens in the fetch step of the cpu cycle when the next instruction is to be loaded from a memory address and the page containing that part of the code is not in memory.

It can also occur when an instruction's operands are being fetched just prior to execution of the instruction.

Or it can happen when an instruction is being excuted in the cpu cycle - for example, an store instruction that moves the value in a cpu register to a (virtual) memory location, but that virtual memory location is not currently in memory.

What happens next?