linux/Documentation/arm64/memory.txt
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   1                     Memory Layout on AArch64 Linux
   2                     ==============================
   3
   4Author: Catalin Marinas <catalin.marinas@arm.com>
   5Date  : 20 February 2012
   6
   7This document describes the virtual memory layout used by the AArch64
   8Linux kernel. The architecture allows up to 4 levels of translation
   9tables with a 4KB page size and up to 3 levels with a 64KB page size.
  10
  11AArch64 Linux uses 3 levels of translation tables with the 4KB page
  12configuration, allowing 39-bit (512GB) virtual addresses for both user
  13and kernel. With 64KB pages, only 2 levels of translation tables are
  14used but the memory layout is the same.
  15
  16User addresses have bits 63:39 set to 0 while the kernel addresses have
  17the same bits set to 1. TTBRx selection is given by bit 63 of the
  18virtual address. The swapper_pg_dir contains only kernel (global)
  19mappings while the user pgd contains only user (non-global) mappings.
  20The swapper_pgd_dir address is written to TTBR1 and never written to
  21TTBR0.
  22
  23
  24AArch64 Linux memory layout:
  25
  26Start                   End                     Size            Use
  27-----------------------------------------------------------------------
  280000000000000000        0000007fffffffff         512GB          user
  29
  30ffffff8000000000        ffffffbbfffeffff        ~240GB          vmalloc
  31
  32ffffffbbffff0000        ffffffbbffffffff          64KB          [guard page]
  33
  34ffffffbc00000000        ffffffbdffffffff           8GB          vmemmap
  35
  36ffffffbe00000000        ffffffbffbbfffff          ~8GB          [guard, future vmmemap]
  37
  38ffffffbffbe00000        ffffffbffbe0ffff          64KB          PCI I/O space
  39
  40ffffffbbffff0000        ffffffbcffffffff          ~2MB          [guard]
  41
  42ffffffbffc000000        ffffffbfffffffff          64MB          modules
  43
  44ffffffc000000000        ffffffffffffffff         256GB          memory
  45
  46
  47Translation table lookup with 4KB pages:
  48
  49+--------+--------+--------+--------+--------+--------+--------+--------+
  50|63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
  51+--------+--------+--------+--------+--------+--------+--------+--------+
  52 |                 |         |         |         |         |
  53 |                 |         |         |         |         v
  54 |                 |         |         |         |   [11:0]  in-page offset
  55 |                 |         |         |         +-> [20:12] L3 index
  56 |                 |         |         +-----------> [29:21] L2 index
  57 |                 |         +---------------------> [38:30] L1 index
  58 |                 +-------------------------------> [47:39] L0 index (not used)
  59 +-------------------------------------------------> [63] TTBR0/1
  60
  61
  62Translation table lookup with 64KB pages:
  63
  64+--------+--------+--------+--------+--------+--------+--------+--------+
  65|63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
  66+--------+--------+--------+--------+--------+--------+--------+--------+
  67 |                 |    |               |              |
  68 |                 |    |               |              v
  69 |                 |    |               |            [15:0]  in-page offset
  70 |                 |    |               +----------> [28:16] L3 index
  71 |                 |    +--------------------------> [41:29] L2 index (only 38:29 used)
  72 |                 +-------------------------------> [47:42] L1 index (not used)
  73 +-------------------------------------------------> [63] TTBR0/1
  74
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