[linux-2.6-block.git] / Documentation / arm64 / memory.txt

		     Memory Layout on AArch64 Linux
		     ==============================

Author: Catalin Marinas <catalin.marinas@arm.com>

This document describes the virtual memory layout used by the AArch64
Linux kernel. The architecture allows up to 4 levels of translation
tables with a 4KB page size and up to 3 levels with a 64KB page size.

AArch64 Linux uses either 3 levels or 4 levels of translation tables
with the 4KB page configuration, allowing 39-bit (512GB) or 48-bit
(256TB) virtual addresses, respectively, for both user and kernel. With
64KB pages, only 2 levels of translation tables, allowing 42-bit (4TB)
virtual address, are used but the memory layout is the same.

User addresses have bits 63:48 set to 0 while the kernel addresses have
the same bits set to 1. TTBRx selection is given by bit 63 of the
virtual address. The swapper_pg_dir contains only kernel (global)
mappings while the user pgd contains only user (non-global) mappings.
The swapper_pg_dir address is written to TTBR1 and never written to
TTBR0.


AArch64 Linux memory layout with 4KB pages + 3 levels:

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	0000007fffffffff	 512GB		user
ffffff8000000000	ffffffffffffffff	 512GB		kernel


AArch64 Linux memory layout with 4KB pages + 4 levels:

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	0000ffffffffffff	 256TB		user
ffff000000000000	ffffffffffffffff	 256TB		kernel


AArch64 Linux memory layout with 64KB pages + 2 levels:

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	000003ffffffffff	   4TB		user
fffffc0000000000	ffffffffffffffff	   4TB		kernel


AArch64 Linux memory layout with 64KB pages + 3 levels:

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	0000ffffffffffff	 256TB		user
ffff000000000000	ffffffffffffffff	 256TB		kernel


For details of the virtual kernel memory layout please see the kernel
booting log.


Translation table lookup with 4KB pages:

+--------+--------+--------+--------+--------+--------+--------+--------+
|63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
+--------+--------+--------+--------+--------+--------+--------+--------+
 |                 |         |         |         |         |
 |                 |         |         |         |         v
 |                 |         |         |         |   [11:0]  in-page offset
 |                 |         |         |         +-> [20:12] L3 index
 |                 |         |         +-----------> [29:21] L2 index
 |                 |         +---------------------> [38:30] L1 index
 |                 +-------------------------------> [47:39] L0 index
 +-------------------------------------------------> [63] TTBR0/1


Translation table lookup with 64KB pages:

+--------+--------+--------+--------+--------+--------+--------+--------+
|63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
+--------+--------+--------+--------+--------+--------+--------+--------+
 |                 |    |               |              |
 |                 |    |               |              v
 |                 |    |               |            [15:0]  in-page offset
 |                 |    |               +----------> [28:16] L3 index
 |                 |    +--------------------------> [41:29] L2 index
 |                 +-------------------------------> [47:42] L1 index
 +-------------------------------------------------> [63] TTBR0/1


When using KVM, the hypervisor maps kernel pages in EL2, at a fixed
offset from the kernel VA (top 24bits of the kernel VA set to zero):

Start			End			Size		Use
-----------------------------------------------------------------------
0000004000000000	0000007fffffffff	 256GB		kernel objects mapped in HYP
Commit	Line	Data
4f04d8f0 CM	1	Memory Layout on AArch64 Linux
	2	==============================
	3
	4	Author: Catalin Marinas <catalin.marinas@arm.com>
4f04d8f0 CM	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
08375198 CM	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
4f04d8f0 CM	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
4f04d8f0 CM	21	TTBR0.
	22
	23
4edae01e	24	AArch64 Linux memory layout with 4KB pages + 3 levels:
4f04d8f0 CM	25
	26	Start End Size Use
	27	-----------------------------------------------------------------------
	28	0000000000000000 0000007fffffffff 512GB user
08375198	29	ffffff8000000000 ffffffffffffffff 512GB kernel
4f04d8f0 CM	30
4f04d8f0 CM	31
4edae01e JL	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
4edae01e JL	38
	39
	40	AArch64 Linux memory layout with 64KB pages + 2 levels:
847264fb CM	41
	42	Start End Size Use
	43	-----------------------------------------------------------------------
	44	0000000000000000 000003ffffffffff 4TB user
08375198	45	fffffc0000000000 ffffffffffffffff 4TB kernel
847264fb	46
847264fb	47
383c2799 CM	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
08375198 CM	56	For details of the virtual kernel memory layout please see the kernel
08375198 CM	57	booting log.
847264fb	58
847264fb	59
08375198	60	Translation table lookup with 4KB pages:
4edae01e JL	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:
4f04d8f0 CM	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
08375198 CM	84	\| \| +--------------------------> [41:29] L2 index
08375198 CM	85	\| +-------------------------------> [47:42] L1 index
4f04d8f0	86	+-------------------------------------------------> [63] TTBR0/1
aa4a73a0	87
08375198	88
aa4a73a0 MZ	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