linux-stable/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 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 63:39 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 + 3 levels:

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		fixed mappings

ffffffbffbe00000	ffffffbffbffffff	   2MB		[guard]

ffffffbffc000000	ffffffbfffffffff	  64MB		modules

ffffffc000000000	ffffffffffffffff	 256GB		kernel logical memory map


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

Start			End			Size		Use
-----------------------------------------------------------------------
0000000000000000	0000ffffffffffff	 256TB		user

ffff000000000000	ffff7bfffffeffff	~124TB		vmalloc

ffff7bffffff0000	ffff7bffffffffff	  64KB		[guard page]

ffff7c0000000000	ffff7dffffffffff	   2TB		vmemmap

ffff7e0000000000	ffff7ffffbbfffff	  ~2TB		[guard, future vmmemap]

ffff7ffffa000000	ffff7ffffaffffff	  16MB		PCI I/O space

ffff7ffffb000000	ffff7ffffbbfffff	  12MB		[guard]

ffff7ffffbc00000	ffff7ffffbdfffff	   2MB		fixed mappings

ffff7ffffbe00000	ffff7ffffbffffff	   2MB		[guard]

ffff7ffffc000000	ffff7fffffffffff	  64MB		modules

ffff800000000000	ffffffffffffffff	 128TB		kernel logical memory map


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

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		fixed mappings

fffffdfffbe00000	fffffdfffbffffff	   2MB		[guard]

fffffdfffc000000	fffffdffffffffff	  64MB		modules

fffffe0000000000	ffffffffffffffff	   2TB		kernel logical memory map


Translation table lookup with 4KB pages + 3 levels:

+--------+--------+--------+--------+--------+--------+--------+--------+
|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 4KB pages + 4 levels:

+--------+--------+--------+--------+--------+--------+--------+--------+
|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 + 2 levels:

+--------+--------+--------+--------+--------+--------+--------+--------+
|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