2012-03-05 04:49:27 -07:00
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Memory Layout on AArch64 Linux
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==============================
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Author: Catalin Marinas <catalin.marinas@arm.com>
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Date : 20 February 2012
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This document describes the virtual memory layout used by the AArch64
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Linux kernel. The architecture allows up to 4 levels of translation
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tables with a 4KB page size and up to 3 levels with a 64KB page size.
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2014-05-12 03:40:44 -06:00
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AArch64 Linux uses either 3 levels or 4 levels of translation tables with
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the 4KB page configuration, allowing 39-bit (512GB) or 48-bit (256TB)
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virtual addresses, respectively, for both user and kernel. With 64KB
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pages, only 2 levels of translation tables, allowing 42-bit (4TB)
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virtual address, are used but the memory layout is the same.
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2012-03-05 04:49:27 -07:00
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User addresses have bits 63:39 set to 0 while the kernel addresses have
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the same bits set to 1. TTBRx selection is given by bit 63 of the
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virtual address. The swapper_pg_dir contains only kernel (global)
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mappings while the user pgd contains only user (non-global) mappings.
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The swapper_pgd_dir address is written to TTBR1 and never written to
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TTBR0.
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2014-05-12 03:40:44 -06:00
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AArch64 Linux memory layout with 4KB pages + 3 levels:
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2012-03-05 04:49:27 -07:00
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Start End Size Use
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-----------------------------------------------------------------------
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0000000000000000 0000007fffffffff 512GB user
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2012-10-23 07:51:16 -06:00
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ffffff8000000000 ffffffbbfffeffff ~240GB vmalloc
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2012-03-05 04:49:27 -07:00
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2012-10-23 07:51:16 -06:00
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ffffffbbffff0000 ffffffbbffffffff 64KB [guard page]
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2012-03-05 04:49:27 -07:00
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2012-10-23 07:51:16 -06:00
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ffffffbc00000000 ffffffbdffffffff 8GB vmemmap
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2012-03-05 04:49:27 -07:00
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2012-10-23 07:51:16 -06:00
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ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap]
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2012-03-05 04:49:27 -07:00
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2014-02-04 09:37:59 -07:00
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ffffffbffa000000 ffffffbffaffffff 16MB PCI I/O space
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ffffffbffb000000 ffffffbffbbfffff 12MB [guard]
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2012-10-23 07:55:08 -06:00
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2014-04-07 16:39:52 -06:00
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ffffffbffbc00000 ffffffbffbdfffff 2MB fixed mappings
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2012-03-05 04:49:27 -07:00
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2014-02-04 09:37:59 -07:00
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ffffffbffbe00000 ffffffbffbffffff 2MB [guard]
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2012-03-05 04:49:27 -07:00
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ffffffbffc000000 ffffffbfffffffff 64MB modules
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2012-10-27 21:30:20 -06:00
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ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map
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2012-03-05 04:49:27 -07:00
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2014-05-12 03:40:44 -06:00
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AArch64 Linux memory layout with 4KB pages + 4 levels:
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Start End Size Use
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-----------------------------------------------------------------------
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0000000000000000 0000ffffffffffff 256TB user
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ffff000000000000 ffff7bfffffeffff ~124TB vmalloc
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ffff7bffffff0000 ffff7bffffffffff 64KB [guard page]
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ffff7c0000000000 ffff7dffffffffff 2TB vmemmap
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ffff7e0000000000 ffff7ffffbbfffff ~2TB [guard, future vmmemap]
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ffff7ffffa000000 ffff7ffffaffffff 16MB PCI I/O space
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ffff7ffffb000000 ffff7ffffbbfffff 12MB [guard]
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ffff7ffffbc00000 ffff7ffffbdfffff 2MB fixed mappings
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ffff7ffffbe00000 ffff7ffffbffffff 2MB [guard]
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ffff7ffffc000000 ffff7fffffffffff 64MB modules
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ffff800000000000 ffffffffffffffff 128TB kernel logical memory map
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AArch64 Linux memory layout with 64KB pages + 2 levels:
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2013-10-23 09:50:07 -06:00
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Start End Size Use
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-----------------------------------------------------------------------
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0000000000000000 000003ffffffffff 4TB user
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fffffc0000000000 fffffdfbfffeffff ~2TB vmalloc
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fffffdfbffff0000 fffffdfbffffffff 64KB [guard page]
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fffffdfc00000000 fffffdfdffffffff 8GB vmemmap
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fffffdfe00000000 fffffdfffbbfffff ~8GB [guard, future vmmemap]
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2014-02-04 09:37:59 -07:00
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fffffdfffa000000 fffffdfffaffffff 16MB PCI I/O space
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fffffdfffb000000 fffffdfffbbfffff 12MB [guard]
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2013-10-23 09:50:07 -06:00
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2014-04-07 16:39:52 -06:00
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fffffdfffbc00000 fffffdfffbdfffff 2MB fixed mappings
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2013-10-23 09:50:07 -06:00
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2014-02-04 09:37:59 -07:00
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fffffdfffbe00000 fffffdfffbffffff 2MB [guard]
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2013-10-23 09:50:07 -06:00
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fffffdfffc000000 fffffdffffffffff 64MB modules
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fffffe0000000000 ffffffffffffffff 2TB kernel logical memory map
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2014-05-12 03:40:44 -06:00
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Translation table lookup with 4KB pages + 3 levels:
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2012-03-05 04:49:27 -07:00
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+--------+--------+--------+--------+--------+--------+--------+--------+
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|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
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+--------+--------+--------+--------+--------+--------+--------+--------+
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| | | | | |
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| | | | | v
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| | | | | [11:0] in-page offset
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| | | | +-> [20:12] L3 index
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| | | +-----------> [29:21] L2 index
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| | +---------------------> [38:30] L1 index
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| +-------------------------------> [47:39] L0 index (not used)
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+-------------------------------------------------> [63] TTBR0/1
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2014-05-12 03:40:44 -06:00
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Translation table lookup with 4KB pages + 4 levels:
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+--------+--------+--------+--------+--------+--------+--------+--------+
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|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
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+--------+--------+--------+--------+--------+--------+--------+--------+
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| | | | | |
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| | | | | v
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| | | | | [11:0] in-page offset
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| | | | +-> [20:12] L3 index
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| | | +-----------> [29:21] L2 index
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| | +---------------------> [38:30] L1 index
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| +-------------------------------> [47:39] L0 index
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+-------------------------------------------------> [63] TTBR0/1
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Translation table lookup with 64KB pages + 2 levels:
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2012-03-05 04:49:27 -07:00
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+--------+--------+--------+--------+--------+--------+--------+--------+
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|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
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+--------+--------+--------+--------+--------+--------+--------+--------+
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| | | | v
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| | | | [15:0] in-page offset
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| | | +----------> [28:16] L3 index
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| | +--------------------------> [41:29] L2 index (only 38:29 used)
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| +-------------------------------> [47:42] L1 index (not used)
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+-------------------------------------------------> [63] TTBR0/1
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2013-05-02 07:31:03 -06:00
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When using KVM, the hypervisor maps kernel pages in EL2, at a fixed
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offset from the kernel VA (top 24bits of the kernel VA set to zero):
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Start End Size Use
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-----------------------------------------------------------------------
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0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP
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