| 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] |
| |
| ffffffbffbc00000 ffffffbffbdfffff 2MB earlyprintk device |
| |
| 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 |
| |
| 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 |
