MIT 6.828 Lab4

Notes of MIT 6.828 Lab4

Part A: Multiprocessor Support and Cooperative Multitasking

Multiprocessor Support

LAPIC and MMIO

Exercise 1

Application Processor Bootstrap

Exercise 2

Question 1

kern/mpentry.S is compiled and linked to run above KERNBASE, which means that its link address will be above KERNBASE. However, it’s actually loaded at physical address MPENTRY_PADDR and starts without virtual memory enabled. Therefore, it must use MPBOOTPHYS to calculate absolute addresses of its symbols.

Per-CPU State and Initialization

Locking

Exercise 5

Question 2

We still need separate kernel stack. Imagine a scenario that a cpu enters the kernel by a trap, it pushes a trapframe onto the kernel stack. If another cpu enters the kernel by a trap at the same time, it also pushes a trapframe onto the kernel stack. If they share the same stack, the two trapframes may overwrite each other.

Round-Robin Scheduling

Exercise 6

Question 3 & 4

1. Because e is located within the kernel stack, and this part of page table is the same among different address spaces.

2. Because the context switch relys on the saving and restoring of the register set. The saving happens at the trapEntry.S and trap(). The restoring happens at env_run() which calls env_pop_tf().