Merge branch 'omap-serial' of git://git.linaro.org/people/rmk/linux-arm
[~shefty/rdma-dev.git] / 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        ffffffbbfffeffff        ~240GB          vmalloc
31
32 ffffffbbffff0000        ffffffbbffffffff          64KB          [guard page]
33
34 ffffffbc00000000        ffffffbdffffffff           8GB          vmemmap
35
36 ffffffbe00000000        ffffffbffbbfffff          ~8GB          [guard, future vmmemap]
37
38 ffffffbffbe00000        ffffffbffbe0ffff          64KB          PCI I/O space
39
40 ffffffbbffff0000        ffffffbcffffffff          ~2MB          [guard]
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