在二级引导器中建立MMU页表数据，目的就是要在内核加载运行之初开启长模式。

    为了简化编程，使用长模式下的2MB分页方式。

    1. #define KINITPAGE_PHYADR 0x1000000
    2. void init_bstartpages(machbstart_t *mbsp)
    3. {
    4.     //顶级页目录
    5.     u64_t *p = (u64_t *)(KINITPAGE_PHYADR); //16MB地址处
    6.     //页目录指针
    7.     u64_t *pdpte = (u64_t *)(KINITPAGE_PHYADR + 0x1000);
    8.     //页目录
    9.     u64_t *pde = (u64_t *)(KINITPAGE_PHYADR + 0x2000);
    10.     //物理地址从0开始
    11.     u64_t adr = 0;
    12.     if (1 > move_krlimg(mbsp, (u64_t)(KINITPAGE_PHYADR), (0x1000 * 16 + 0x2000)))
    13.     {
    14.         kerror("move_krling err");
    15.     }
    16.     //将顶级页目录、页目录指针的空间清0
    17.     for (uint_t mi = 0; mi < PGENTY_SIZE; mi++)
    18.     {
    19.         p[mi] = 0;
    20.         pdpte[mi] = 0;
    21.     }
    23.     //映射
    24.     for (uint_t pdei = 0; pdei < 16; pdei++)
    25.     {
    26.         pdpte[pdei] = (u64_t)((u32_t)pde | KPDPTE_RW | KPDPTE_P);
    27.         for (uint_t pdeii = 0; pdeii < PGENTY_SIZE; pdeii++)
    28.         {
    29.             //大页KPDE_PS 2MB， 可读写KPDE_RW, 存在KPDE_P
    30.             pde[pdeii] = 0 | adr | KPDE_PS | KPDE_RW | KPDE_P;
    31.             adr += 0x200000;
    32.         }
    33.         pde = (u64_t *)((u32_t)pde + 0x1000);
    34.     }
    36.     //让顶级页目录中第0项和第((KRNL_VIRTUAL_ADDRESS_START) >> KPML4_SHIFT)&0x1ff项，指向同一个页目录指针页
    37.     p[((KRNL_VIRTUAL_ADDRESS_START)>>KPML_4_SHIFT)&0x1ff] = (u64_t)((u32_t)pdpte | KPML4_RW | KPML4_P);
    38.     p[0] = (u64_t)((u32_t)pdpte | KPML4_RW | KPML4_P);
    39.     //把页表首地址保存在机器信息结构中。
    40.     mbsp->mb_pml4padr = (u64_t)(KINITPAGE_PHYADR);
    41.     mbsp->mb_subpageslen = (u64_t)(0x1000 * 16 + 0x2000);
    42.     mbsp->mb_kpmapphymemsz = (u64_t)(0x400000000);
    43.     return;
    44. }