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1 | Memory Layout on AArch64 Linux |
2 | ============================== | |
3 | ||
4 | Author: Catalin Marinas <catalin.marinas@arm.com> | |
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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 | ||
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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) | |
4edae01e | 14 | virtual address, are used but the memory layout is the same. |
4f04d8f0 | 15 | |
08375198 | 16 | User addresses have bits 63:48 set to 0 while the kernel addresses have |
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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. | |
a24637d5 | 20 | The swapper_pg_dir address is written to TTBR1 and never written to |
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21 | TTBR0. |
22 | ||
23 | ||
4edae01e | 24 | AArch64 Linux memory layout with 4KB pages + 3 levels: |
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25 | |
26 | Start End Size Use | |
27 | ----------------------------------------------------------------------- | |
28 | 0000000000000000 0000007fffffffff 512GB user | |
08375198 | 29 | ffffff8000000000 ffffffffffffffff 512GB kernel |
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30 | |
31 | ||
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32 | AArch64 Linux memory layout with 4KB pages + 4 levels: |
33 | ||
34 | Start End Size Use | |
35 | ----------------------------------------------------------------------- | |
36 | 0000000000000000 0000ffffffffffff 256TB user | |
08375198 | 37 | ffff000000000000 ffffffffffffffff 256TB kernel |
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38 | |
39 | ||
40 | AArch64 Linux memory layout with 64KB pages + 2 levels: | |
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41 | |
42 | Start End Size Use | |
43 | ----------------------------------------------------------------------- | |
44 | 0000000000000000 000003ffffffffff 4TB user | |
08375198 | 45 | fffffc0000000000 ffffffffffffffff 4TB kernel |
847264fb | 46 | |
847264fb | 47 | |
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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 | ||
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56 | For details of the virtual kernel memory layout please see the kernel |
57 | booting log. | |
847264fb | 58 | |
847264fb | 59 | |
08375198 | 60 | Translation table lookup with 4KB pages: |
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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 | ||
08375198 | 75 | Translation table lookup with 64KB pages: |
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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 | |
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84 | | | +--------------------------> [41:29] L2 index |
85 | | +-------------------------------> [47:42] L1 index | |
4f04d8f0 | 86 | +-------------------------------------------------> [63] TTBR0/1 |
aa4a73a0 | 87 | |
08375198 | 88 | |
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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 |