+---------------------------+
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                                                               |                           |                                                   +-------------------+----------------+  <-------+ 0x00000000
                                                               |                           |                                                   |                   |                |
                                                               |                           |                                                   |                   |   reserved     |
                                                               |                           |                                                   |                   |                |
                                                               |                           |                                                   |                   +----------------+  <-------+ 0x00080000(img_start, init_start)
                                                               |                           |                                                   |                   |                |
                                                               |                           |                                                   |                   |   bootloader   |
                                                               |                           |                                                   |                   |                |
                                                               |                           |                                                   |                   +----------------+  <--------+init_end
                                                               |                           |                                                   |                   |                |
                                                               |                           |        KVADDR=0xffffff0000000000   <--------------+                   |  KERNEL IMG    |
--------------------+---------------------------------- -------------------------------------------------+                                                         |                |                                                                                          ------------------------------------------------------------------------------------------------+
                    |                                          |                           |             |                                                         +----------------+  <--------+metadata_start (img_end)  (img_end─+─(npages─*◄sizeof(structapage))g_end)                                                                                                     |
                    |       256M已经映射为内核空间             |                           |             |                                                         |                |                                                                                                                                                                                          |
                    |                       |           -      |                           |             |                                                         | page metadata  |                                                                                                                                                                                          |
                    |       整体500多Ｍ是进行了|page的管理       |                           |             |                                                         |                |                                                                                                                                                                                          |
                    |                       ||                 |                           |             |                                                         +----------------+  <--------+metadata_end                                                                                                                                                                  |
                    |                       |                  |                           |             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  |                           |             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  |                           |             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  |                           |             |                                                         |     pages      |                                                                                                                                                                                          |
                    |                       |                  +---------------------------+             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  |                           |             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  |                           |             |                                                         |                |                                                                                                                                                                                          |
内核空间＋内核空洞＝512M                      |                  |    page matedata          |             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  |                           |             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  +---------------------------+             |                                                         |                |                                                                                                                                                                                          |
                    |                       |                  +---------------------------+             |                                                         +----------------+ <--------+page_end (metadata_end + (npages * PAGE_SIZE))                                                                                                                                 |
                    |                       |                  |                           |             |                                                         +----------------+                                                                                                                                                                                          |
                    |                       +------------------------------------------------------------++                                                        |                |  <------+ PERIPHERAL_BASE [512M, 1G]                                                                                                                                                     |
                    |                       |                  |                           |              |                                                        |                |           0x2000_0000                                                                                                                                                                    |
                    |                       |                  |     pages                 |128x1000x4KB =|500M                                                    |                |                                                                                                                                                                                          |
                    |   256-512的地址空洞需要|map_kernel_space  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |   进行映射            |                  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |                       |                  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |                       |                  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |                       |                  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |                       |                  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |                       |                  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |                       |                  |                           |              |                                                        |                |                                                                                                                                                                                          |
                    |                       |                  +-----------------------------+            |                                                        |                |    <---+  PHYSMEM_END                                                                                                                                                                    |
    +---------------+-----------------------+-------------------------------------------------------------+                                    --------------------------------------+                                                                                                                                                                                         |
                                                               |                           |                                                  +-                   |                |           0x4000_0000                                                                                                                                                                    |
                                                               |                           | <-------+ PERIPHERAL_BASE [512M, 1G              |                    |                |                                                                                                                                                                                          |
                                                               |                           |                                                  |                    |                |                                                                                                                                                                                          |
                                                               |                           |                                                  |                    |                |                                                                                                                                                                                          |
                                                               |                           |                                                  |                    |                |                                                                                                                                                                                          |
                         [512M, 1G]已经映射为设备空间          |                           |                                                  |                    |                |                                                                                                                                                                                          |
                                                               |                           |                                                  |       +------------+----------------+           0xFFFF_FFFF-                                                                                                                                                                   |
                                                               |                           |                                                  |       |                                                                                                                                                                                                                        |
                                                               |                           |                                                  |       |                                                                                                                                                                                                                        |
                                                               |                           |                                                  |       |                                                                                                                                                                                                                        |
                                                               |                           |                                                  |       |                                                                                                                                                                                                                        |
                                                               |                           |                                                  |       |                                                                                                                                                                                                                        |
     +-------------------------------------------------------+ +---------------------------+   <---+  PHYSMEM_END <---------------------------+       |                                                                                                                                                                                                                        |
                                                               |                           |                                                          |                                                                                                                                                                                                                        |
                                                               |                           |                                                          |                                                                                                                                                                                                                        |
                物理地址0x4000_0000 ... 0xFFFF_FFFF在          |                           |                                                          |                                                                                                                                                                                                                        |
                此处映射为1G的空间，　local peripherals          |                           |                                                          |                                                                                                                                                                                                                        |
                                                               |                           |                                                          |                                                                                                                                                                                                                        |
                                                               |                           |                                                          |                                                                                                                                                                                                                        |
    +----------------------------------------------------------+---------------------------++   +-----------------------------------------------------+                                                                                                                                                                                                                        |
    +                                                                                                                                                                                                                                                                                                                                                                          |
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                                                                               +-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+