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

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

Author: Catalin Marinas <catalin.marinas@arm.com>
Date  : 20 February 2012

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 3 levels of translation tables with the 4KB page
configuration, allowing 39-bit (512GB) virtual addresses for both user
and kernel. With 64KB pages, only 2 levels of translation tables are
used but the memory layout is the same.

User addresses have bits 63:39 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_pgd_dir address is written to TTBR1 and never written to
TTBR0.


AArch64 Linux memory layout with 4KB pages:

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	0000007fffffffff	 512GB		user

ffffff8000000000	ffffffbbfffeffff	~240GB		vmalloc

ffffffbbffff0000	ffffffbbffffffff	  64KB		[guard page]

ffffffbc00000000	ffffffbdffffffff	   8GB		vmemmap

ffffffbe00000000	ffffffbffbbfffff	  ~8GB		[guard, future vmmemap]

ffffffbffbc00000	ffffffbffbdfffff	   2MB		earlyprintk device

ffffffbffbe00000	ffffffbffbe0ffff	  64KB		PCI I/O space

ffffffbffbe10000	ffffffbcffffffff	  ~2MB		[guard]

ffffffbffc000000	ffffffbfffffffff	  64MB		modules

ffffffc000000000	ffffffffffffffff	 256GB		kernel logical memory map


AArch64 Linux memory layout with 64KB pages:

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	000003ffffffffff	   4TB		user

fffffc0000000000	fffffdfbfffeffff	  ~2TB		vmalloc

fffffdfbffff0000	fffffdfbffffffff	  64KB		[guard page]

fffffdfc00000000	fffffdfdffffffff	   8GB		vmemmap

fffffdfe00000000	fffffdfffbbfffff	  ~8GB		[guard, future vmmemap]

fffffdfffbc00000	fffffdfffbdfffff	   2MB		earlyprintk device

fffffdfffbe00000	fffffdfffbe0ffff	  64KB		PCI I/O space

fffffdfffbe10000	fffffdfffbffffff	  ~2MB		[guard]

fffffdfffc000000	fffffdffffffffff	  64MB		modules

fffffe0000000000	ffffffffffffffff	   2TB		kernel logical memory map


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 (not used)
 +-------------------------------------------------> [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 (only 38:29 used)
 |                 +-------------------------------> [47:42] L1 index (not used)
 +-------------------------------------------------> [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>
	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
847264fb	24	AArch64 Linux memory layout with 4KB pages:
4f04d8f0 CM	25
	26	Start End Size Use
	27	-----------------------------------------------------------------------
	28	0000000000000000 0000007fffffffff 512GB user
	29
e3978cde	30	ffffff8000000000 ffffffbbfffeffff ~240GB vmalloc
4f04d8f0	31
e3978cde	32	ffffffbbffff0000 ffffffbbffffffff 64KB [guard page]
4f04d8f0	33
e3978cde	34	ffffffbc00000000 ffffffbdffffffff 8GB vmemmap
4f04d8f0	35
e3978cde	36	ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap]
4f04d8f0	37
2475ff9d CM	38	ffffffbffbc00000 ffffffbffbdfffff 2MB earlyprintk device
2475ff9d CM	39
e3978cde	40	ffffffbffbe00000 ffffffbffbe0ffff 64KB PCI I/O space
4f04d8f0	41
e29a074b	42	ffffffbffbe10000 ffffffbcffffffff ~2MB [guard]
4f04d8f0 CM	43
	44	ffffffbffc000000 ffffffbfffffffff 64MB modules
	45
715a7119	46	ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map
4f04d8f0 CM	47
4f04d8f0 CM	48
847264fb CM	49	AArch64 Linux memory layout with 64KB pages:
	50
	51	Start End Size Use
	52	-----------------------------------------------------------------------
	53	0000000000000000 000003ffffffffff 4TB user
	54
	55	fffffc0000000000 fffffdfbfffeffff ~2TB vmalloc
	56
	57	fffffdfbffff0000 fffffdfbffffffff 64KB [guard page]
	58
	59	fffffdfc00000000 fffffdfdffffffff 8GB vmemmap
	60
	61	fffffdfe00000000 fffffdfffbbfffff ~8GB [guard, future vmmemap]
	62
	63	fffffdfffbc00000 fffffdfffbdfffff 2MB earlyprintk device
	64
	65	fffffdfffbe00000 fffffdfffbe0ffff 64KB PCI I/O space
	66
	67	fffffdfffbe10000 fffffdfffbffffff ~2MB [guard]
	68
	69	fffffdfffc000000 fffffdffffffffff 64MB modules
	70
	71	fffffe0000000000 ffffffffffffffff 2TB kernel logical memory map
	72
	73
4f04d8f0 CM	74	Translation table lookup with 4KB pages:
	75
	76	+--------+--------+--------+--------+--------+--------+--------+--------+
	77	\|63 56\|55 48\|47 40\|39 32\|31 24\|23 16\|15 8\|7 0\|
	78	+--------+--------+--------+--------+--------+--------+--------+--------+
	79	\| \| \| \| \| \|
	80	\| \| \| \| \| v
	81	\| \| \| \| \| [11:0] in-page offset
	82	\| \| \| \| +-> [20:12] L3 index
	83	\| \| \| +-----------> [29:21] L2 index
	84	\| \| +---------------------> [38:30] L1 index
	85	\| +-------------------------------> [47:39] L0 index (not used)
	86	+-------------------------------------------------> [63] TTBR0/1
	87
	88
	89	Translation table lookup with 64KB pages:
	90
	91	+--------+--------+--------+--------+--------+--------+--------+--------+
	92	\|63 56\|55 48\|47 40\|39 32\|31 24\|23 16\|15 8\|7 0\|
	93	+--------+--------+--------+--------+--------+--------+--------+--------+
	94	\| \| \| \| \|
	95	\| \| \| \| v
	96	\| \| \| \| [15:0] in-page offset
	97	\| \| \| +----------> [28:16] L3 index
	98	\| \| +--------------------------> [41:29] L2 index (only 38:29 used)
	99	\| +-------------------------------> [47:42] L1 index (not used)
	100	+-------------------------------------------------> [63] TTBR0/1
aa4a73a0 MZ	101
	102	When using KVM, the hypervisor maps kernel pages in EL2, at a fixed
	103	offset from the kernel VA (top 24bits of the kernel VA set to zero):
	104
	105	Start End Size Use
	106	-----------------------------------------------------------------------
	107	0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP