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1 Memory Layout on AArch64 Linux
2 ==============================
3
4 Author: Catalin Marinas <catalin.marinas@arm.com>
5
6 This document describes the virtual memory layout used by the AArch64
7 Linux kernel. The architecture allows up to 4 levels of translation
8 tables with a 4KB page size and up to 3 levels with a 64KB page size.
9
10 AArch64 Linux uses either 3 levels or 4 levels of translation tables
11 with the 4KB page configuration, allowing 39-bit (512GB) or 48-bit
12 (256TB) virtual addresses, respectively, for both user and kernel. With
13 64KB pages, only 2 levels of translation tables, allowing 42-bit (4TB)
14 virtual address, are used but the memory layout is the same.
15
16 User addresses have bits 63:48 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_pg_dir address is written to TTBR1 and never written to
21 TTBR0.
22
23
24 AArch64 Linux memory layout with 4KB pages + 3 levels:
25
26 Start End Size Use
27 -----------------------------------------------------------------------
28 0000000000000000 0000007fffffffff 512GB user
29 ffffff8000000000 ffffffffffffffff 512GB kernel
30
31
32 AArch64 Linux memory layout with 4KB pages + 4 levels:
33
34 Start End Size Use
35 -----------------------------------------------------------------------
36 0000000000000000 0000ffffffffffff 256TB user
37 ffff000000000000 ffffffffffffffff 256TB kernel
38
39
40 AArch64 Linux memory layout with 64KB pages + 2 levels:
41
42 Start End Size Use
43 -----------------------------------------------------------------------
44 0000000000000000 000003ffffffffff 4TB user
45 fffffc0000000000 ffffffffffffffff 4TB kernel
46
47
48 AArch64 Linux memory layout with 64KB pages + 3 levels:
49
50 Start End Size Use
51 -----------------------------------------------------------------------
52 0000000000000000 0000ffffffffffff 256TB user
53 ffff000000000000 ffffffffffffffff 256TB kernel
54
55
56 For details of the virtual kernel memory layout please see the kernel
57 booting log.
58
59
60 Translation table lookup with 4KB pages:
61
62 +--------+--------+--------+--------+--------+--------+--------+--------+
63 |63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
64 +--------+--------+--------+--------+--------+--------+--------+--------+
65 | | | | | |
66 | | | | | v
67 | | | | | [11:0] in-page offset
68 | | | | +-> [20:12] L3 index
69 | | | +-----------> [29:21] L2 index
70 | | +---------------------> [38:30] L1 index
71 | +-------------------------------> [47:39] L0 index
72 +-------------------------------------------------> [63] TTBR0/1
73
74
75 Translation table lookup with 64KB pages:
76
77 +--------+--------+--------+--------+--------+--------+--------+--------+
78 |63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
79 +--------+--------+--------+--------+--------+--------+--------+--------+
80 | | | | |
81 | | | | v
82 | | | | [15:0] in-page offset
83 | | | +----------> [28:16] L3 index
84 | | +--------------------------> [41:29] L2 index
85 | +-------------------------------> [47:42] L1 index
86 +-------------------------------------------------> [63] TTBR0/1
87
88
89 When using KVM, the hypervisor maps kernel pages in EL2, at a fixed
90 offset from the kernel VA (top 24bits of the kernel VA set to zero):
91
92 Start End Size Use
93 -----------------------------------------------------------------------
94 0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP