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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 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:
- 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]
- ffffffbffbe00000 ffffffbffbe0ffff 64KB PCI I/O space
- ffffffbbffff0000 ffffffbcffffffff ~2MB [guard]
- ffffffbffc000000 ffffffbfffffffff 64MB modules
- ffffffc000000000 ffffffffffffffff 256GB 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
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