+-----------------------------------------------------+
                                                                                                                                                                      | TIPS:u64 boot_ttbr1_l0,                             |
                                                                                                                                                                      |          boot_ttbr1_l1,                             |
                                                                           VA                                         PA                                              |          boot_ttbr1_l2                              |
                                                                                                                                                                      | 地址都在bootloader内。                               |
                            内核空间映射[直接以2M页粒度永久映射]                                                                                                      |                                                     |
                                                                                       KVADDR=0xffffff0000000000                                                      |                                                     |
                                                                      +---------------+   ------------------->   +--------------+           PA:0x0000_0000            | 以上定义表明：页表页的地址和(L0, L1)页表项的填充都是 |
                                                                      |               |                          |              |                                     | bootloader范围内的物理地址. 当然L2填充的是[0,256M]的|
                                                                      |               |                          |              |                                     | 物理地址，对应了[KVADDR, KVADDR+256M]                |
                                                                      |               |                          |              |                                     |                                                     |
                                                                      |               |                          |              |                                     | 以上是固定分配，与后面空洞映射采用页的方式不一样。    |
                                                                      |               |                          |              |                                     |                                                     |
                                                                      |               |                          |              |                                     | 虽然本质上都是virt = phys + kvaddr.但是页的方式更加 |
                                                                      |               |         MMU              |              |                                     | 的灵活.                                             |
                                                                      |     256M      |                          |              |                                     |                                                     |
                                                                      |               |                          |              |                                     |                                                     |
                                                                      |               |                          |              |                                     |                                                     |
                                                                      |               |                          |              |                                     |                                                     |
                                                                      |               |                          |              |                                     +-----------------------------------------------------+
                                                                      |               |                          |              |
                                                                      |               |                          |              |
                                                                      |               |                          |              |
                                             +------------------------+---------------+--------------------------+--------------+-----+      PA:PHYSMEM_BOOT_END 0x1000_0000



                                          boot_ttbr1_l0                                boot_ttbr1_l1                                      boot_ttbr1_l2                                                  PA:0x0000_0000
                                              +-------->  +--------------------+        +------------>  +---------------------------+                                        per idx
                                              |           |                    | GET_L1_INDEX(kva),idx=0|              |----------------------------->  +---------------+                    +--------------------------+
                                              |           |                    |        |               +---------------------------+                   |----------------------------------> |                          | 2M
                                              |           |                    |        |               |                           |                   |---------------|                    +--------------------------+
                                              |           |                    |        |               |                           |                   |--------------------------------->  |                          |
                                              |           |                    |        |               |                           |                   |---------------|                    |                          | 2M
                                              |           |                    |        |               |                           |                   |---------------|                    +--------------------------+
                                              |           +--------------------+        |               |                           |                   |---------------|                    |                          |
 L0    L1    L2       2M       GET_L0_INDEX(kva), idx=510 |            |-----------------               |                           |                   |---------------|                    |                          | 2M
+----+-----+-----+------------+               |           +--------------------|                        |                           |                   |---------------|                    +--------------------------+
|    |     |     |            |               |           +--------------------+                        +---------------------------+                   |---------------|                    |                          |
+----+-----+-----+------------+               |                                                                                                         |---------------|                    |                          |
            KVADDR                            |                     L0 PTP                                          L1 PTP                              |---------------|                    +--------------------------+
             +            +---------------------------+                                                                                                 +---------------+                    |                          |
             |            |                   |       |                                                                                                        L2 PTP                        |                          |
             |            |                   |       |                                                                                                                                      +--------------------------+
             |            |               +---+-------+                                                                                                                                      |                         ++
             |            |   MMU         |ttbr1_el1  |                                                                                                                                      |                          |
             +----------> |               +-----------+                                                                                                                                     +---------------------------+
                          |                           |                                                                                                                                      |                          |
                          |                           |                                                                                                                                      |                          |
                          +---------------------------+                                                                                                                                      |                          |
                                                                                                                                                                                             |                          |
                                                                                                                                                                                             |                          |
                                                                                                                                                                                             |                          |
                                                                                                                                                                                             +--------------------------+