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|
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
|
