Per-CPU State and Initialization

Exercise 3. Modify mem_init_mp() (in kern/pmap.c) to map per-CPU stacks starting at KSTACKTOP, as shown in inc/memlayout.h. The size of each stack is KSTKSIZE bytes plus KSTKGAP bytes of unmapped guard pages. Your code should pass the new check in check_kern_pgdir().

static void
mem_init_mp(void)
{
    int i;
    for (i = 0; i < NCPU; ++i) {
        boot_map_region(kern_pgdir, 
            KSTACKTOP - KSTKSIZE - i * (KSTKSIZE + KSTKGAP), 
            KSTKSIZE, 
            PADDR(percpu_kstacks[i]), 
            PTE_W);
    }
}

Exercise 4. The code in trap_init_percpu() (kern/trap.c) initializes the TSS and TSS descriptor for the BSP. It worked in Lab 3, but is incorrect when running on other CPUs. Change the code so that it can work on all CPUs. (Note: your new code should not use the global ts variable any more.)

void
trap_init_percpu(void)
{
    int cid = thiscpu->cpu_id;
    thiscpu->cpu_ts.ts_esp0 = KSTACKTOP - cid * (KSTKSIZE + KSTKGAP);
    thiscpu->cpu_ts.ts_ss0 = GD_KD;
    gdt[(GD_TSS0 >> 3)+cid] = SEG16(STS_T32A, (uint32_t) (&(thiscpu->cpu_ts)),
                    sizeof(struct Taskstate), 0);
    gdt[(GD_TSS0 >> 3)+cid].sd_s = 0;
    ltr(GD_TSS0+8*cid);
    lidt(&idt_pd);
}