Exercise 1：

// Where to start the next region.  Initially, this is the
    // beginning of the MMIO region.  Because this is static, its
    // value will be preserved between calls to mmio_map_region
    // (just like nextfree in boot_alloc).
    static uintptr_t base = MMIOBASE;

    // Reserve size bytes of virtual memory starting at base and
    
 
// map physical pages [pa,pa+size) to virtual addresses
    // [base,base+size).  Since this is device memory and not
    // regular DRAM, you'll have to tell the CPU that it isn't
    // safe to cache access to this memory.  Luckily, the page
    // tables provide bits for this purpose; simply create the
    
 
// mapping with PTE_PCD|PTE_PWT (cache-disable and
    // write-through) in addition to PTE_W.  (If you're interested
    // in more details on this, see section 10.5 of IA32 volume
    // 3A.)
    //
    // Be sure to round size up to a multiple of PGSIZE and to
    // handle if this reservation would overflow MMIOLIM (it's
    
 
// okay to simply panic if this happens).
    //
    // Hint: The staff solution uses boot_map_region.
    //
    // Your code here:

    void* ret = (void*)base;

    size = ROUNDUP(size, PGSIZE);
    if (base + size > MMIOLIM || base + size < base)
        panic("mmio_map_region: reservation overflow\n");

    boot_map_region(kern_pgdir, base, size, pa,  PTE_PCD | PTE_PWT |PTE_W );
    base += size;

    return ret;
    //panic("mmio_map_region not implemented");

exercise2：

size_t i;
    //Mark physical page 0 as in use.
    pages[0].pp_ref = 1;
    pages[0].pp_link = NULL;
    
    size_t lowio= IOPHYSMEM / PGSIZE;
    size_t  highio = EXTPHYSMEM / PGSIZE;
    
    for (i = 1; i < npages; i++)
    {
        if ( (i == MPENTRY_PADDR / PGSIZE)||(i >= lowio && i < highio) || (i >= EXTPHYSMEM / PGSIZE && i < PADDR(boot_alloc(0)) / PGSIZE))
        {
            pages[i].pp_ref = 1;
            pages[i].pp_link = NULL;
        }
                
        else {
            pages[i].pp_ref = 0;
            pages[i].pp_link = page_free_list;
            page_free_list = &pages[i];
        }

    }