[mirror_ubuntu-jammy-kernel.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]

ffffffbffa000000	ffffffbffaffffff	  16MB		PCI I/O space

ffffffbffb000000	ffffffbffbbfffff	  12MB		[guard]

ffffffbffbc00000	ffffffbffbdfffff	   2MB		earlyprintk device

ffffffbffbe00000	ffffffbffbffffff	   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]

fffffdfffa000000	fffffdfffaffffff	  16MB		PCI I/O space

fffffdfffb000000	fffffdfffbbfffff	  12MB		[guard]

fffffdfffbc00000	fffffdfffbdfffff	   2MB		earlyprintk device

fffffdfffbe00000	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
22bd1c91 CM	38	ffffffbffa000000 ffffffbffaffffff 16MB PCI I/O space
	39
	40	ffffffbffb000000 ffffffbffbbfffff 12MB [guard]
2475ff9d	41
22bd1c91	42	ffffffbffbc00000 ffffffbffbdfffff 2MB earlyprintk device
4f04d8f0	43
22bd1c91	44	ffffffbffbe00000 ffffffbffbffffff 2MB [guard]
4f04d8f0 CM	45
	46	ffffffbffc000000 ffffffbfffffffff 64MB modules
	47
715a7119	48	ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map
4f04d8f0 CM	49
4f04d8f0 CM	50
847264fb CM	51	AArch64 Linux memory layout with 64KB pages:
	52
	53	Start End Size Use
	54	-----------------------------------------------------------------------
	55	0000000000000000 000003ffffffffff 4TB user
	56
	57	fffffc0000000000 fffffdfbfffeffff ~2TB vmalloc
	58
	59	fffffdfbffff0000 fffffdfbffffffff 64KB [guard page]
	60
	61	fffffdfc00000000 fffffdfdffffffff 8GB vmemmap
	62
	63	fffffdfe00000000 fffffdfffbbfffff ~8GB [guard, future vmmemap]
	64
22bd1c91 CM	65	fffffdfffa000000 fffffdfffaffffff 16MB PCI I/O space
	66
	67	fffffdfffb000000 fffffdfffbbfffff 12MB [guard]
847264fb	68
22bd1c91	69	fffffdfffbc00000 fffffdfffbdfffff 2MB earlyprintk device
847264fb	70
22bd1c91	71	fffffdfffbe00000 fffffdfffbffffff 2MB [guard]
847264fb CM	72
	73	fffffdfffc000000 fffffdffffffffff 64MB modules
	74
	75	fffffe0000000000 ffffffffffffffff 2TB kernel logical memory map
	76
	77
4f04d8f0 CM	78	Translation table lookup with 4KB pages:
	79
	80	+--------+--------+--------+--------+--------+--------+--------+--------+
	81	\|63 56\|55 48\|47 40\|39 32\|31 24\|23 16\|15 8\|7 0\|
	82	+--------+--------+--------+--------+--------+--------+--------+--------+
	83	\| \| \| \| \| \|
	84	\| \| \| \| \| v
	85	\| \| \| \| \| [11:0] in-page offset
	86	\| \| \| \| +-> [20:12] L3 index
	87	\| \| \| +-----------> [29:21] L2 index
	88	\| \| +---------------------> [38:30] L1 index
	89	\| +-------------------------------> [47:39] L0 index (not used)
	90	+-------------------------------------------------> [63] TTBR0/1
	91
	92
	93	Translation table lookup with 64KB pages:
	94
	95	+--------+--------+--------+--------+--------+--------+--------+--------+
	96	\|63 56\|55 48\|47 40\|39 32\|31 24\|23 16\|15 8\|7 0\|
	97	+--------+--------+--------+--------+--------+--------+--------+--------+
	98	\| \| \| \| \|
	99	\| \| \| \| v
	100	\| \| \| \| [15:0] in-page offset
	101	\| \| \| +----------> [28:16] L3 index
	102	\| \| +--------------------------> [41:29] L2 index (only 38:29 used)
	103	\| +-------------------------------> [47:42] L1 index (not used)
	104	+-------------------------------------------------> [63] TTBR0/1
aa4a73a0 MZ	105
	106	When using KVM, the hypervisor maps kernel pages in EL2, at a fixed
	107	offset from the kernel VA (top 24bits of the kernel VA set to zero):
	108
	109	Start End Size Use
	110	-----------------------------------------------------------------------
	111	0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP