Documentation/arm64/memory.txt

   1                      Memory Layout on AArch64 Linux
   2                      ==============================
   3
   4 Author: Catalin Marinas <catalin.marinas@arm.com>
   5 Date  : 20 February 2012
   6
   7 This document describes the virtual memory layout used by the AArch64
   8 Linux kernel. The architecture allows up to 4 levels of translation
   9 tables with a 4KB page size and up to 3 levels with a 64KB page size.
  10
  11 AArch64 Linux uses 3 levels of translation tables with the 4KB page
  12 configuration, allowing 39-bit (512GB) virtual addresses for both user
  13 and kernel. With 64KB pages, only 2 levels of translation tables are
  14 used but the memory layout is the same.
  15
  16 User addresses have bits 63:39 set to 0 while the kernel addresses have
  17 the same bits set to 1. TTBRx selection is given by bit 63 of the
  18 virtual address. The swapper_pg_dir contains only kernel (global)
  19 mappings while the user pgd contains only user (non-global) mappings.
  20 The swapper_pgd_dir address is written to TTBR1 and never written to
  21 TTBR0.
  22
  23
  24 AArch64 Linux memory layout:
  25
  26 Start                   End                     Size            Use
  27 -----------------------------------------------------------------------
  28 0000000000000000        0000007fffffffff         512GB          user
  29
  30 ffffff8000000000        ffffffbbfffcffff        ~240GB          vmalloc
  31
  32 ffffffbbfffd0000        ffffffbcfffdffff          64KB          [guard page]
  33
  34 ffffffbbfffe0000        ffffffbcfffeffff          64KB          PCI I/O space
  35
  36 ffffffbbffff0000        ffffffbcffffffff          64KB          [guard page]
  37
  38 ffffffbc00000000        ffffffbdffffffff           8GB          vmemmap
  39
  40 ffffffbe00000000        ffffffbffbffffff          ~8GB          [guard, future vmmemap]
  41
  42 ffffffbffc000000        ffffffbfffffffff          64MB          modules
  43
  44 ffffffc000000000        ffffffffffffffff         256GB          memory
  45
  46
  47 Translation 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
  62 Translation 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