About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / arm64 / memory.txt




Custom Search

Based on kernel version 3.19. Page generated on 2015-02-13 21:16 EST.

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
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.