1 Memory Layout on AArch64 Linux 2 ============================== 3 4Author: Catalin Marinas <catalin.marinas@arm.com> 5Date : 20 February 2012 6 7This document describes the virtual memory layout used by the AArch64 8Linux kernel. The architecture allows up to 4 levels of translation 9tables with a 4KB page size and up to 3 levels with a 64KB page size. 10 11AArch64 Linux uses 3 levels of translation tables with the 4KB page 12configuration, allowing 39-bit (512GB) virtual addresses for both user 13and kernel. With 64KB pages, only 2 levels of translation tables are 14used but the memory layout is the same. 15 16User addresses have bits 63:39 set to 0 while the kernel addresses have 17the same bits set to 1. TTBRx selection is given by bit 63 of the 18virtual address. The swapper_pg_dir contains only kernel (global) 19mappings while the user pgd contains only user (non-global) mappings. 20The swapper_pgd_dir address is written to TTBR1 and never written to 21TTBR0. 22 23 24AArch64 Linux memory layout with 4KB pages: 25 26Start End Size Use 27----------------------------------------------------------------------- 280000000000000000 0000007fffffffff 512GB user 29 30ffffff8000000000 ffffffbbfffeffff ~240GB vmalloc 31 32ffffffbbffff0000 ffffffbbffffffff 64KB [guard page] 33 34ffffffbc00000000 ffffffbdffffffff 8GB vmemmap 35 36ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap] 37 38ffffffbffa000000 ffffffbffaffffff 16MB PCI I/O space 39 40ffffffbffb000000 ffffffbffbbfffff 12MB [guard] 41 42ffffffbffbc00000 ffffffbffbdfffff 2MB fixed mappings 43 44ffffffbffbe00000 ffffffbffbffffff 2MB [guard] 45 46ffffffbffc000000 ffffffbfffffffff 64MB modules 47 48ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map 49 50 51AArch64 Linux memory layout with 64KB pages: 52 53Start End Size Use 54----------------------------------------------------------------------- 550000000000000000 000003ffffffffff 4TB user 56 57fffffc0000000000 fffffdfbfffeffff ~2TB vmalloc 58 59fffffdfbffff0000 fffffdfbffffffff 64KB [guard page] 60 61fffffdfc00000000 fffffdfdffffffff 8GB vmemmap 62 63fffffdfe00000000 fffffdfffbbfffff ~8GB [guard, future vmmemap] 64 65fffffdfffa000000 fffffdfffaffffff 16MB PCI I/O space 66 67fffffdfffb000000 fffffdfffbbfffff 12MB [guard] 68 69fffffdfffbc00000 fffffdfffbdfffff 2MB fixed mappings 70 71fffffdfffbe00000 fffffdfffbffffff 2MB [guard] 72 73fffffdfffc000000 fffffdffffffffff 64MB modules 74 75fffffe0000000000 ffffffffffffffff 2TB kernel logical memory map 76 77 78Translation table lookup with 4KB pages: 79 80+--------+--------+--------+--------+--------+--------+--------+--------+ 81|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| 82+--------+--------+--------+--------+--------+--------+--------+--------+ 83 | | | | | | 84 | | | | | v 85 | | | | | [11:0] in-page offset 86 | | | | +-> [20:12] L3 index 87 | | | +-----------> [29:21] L2 index 88 | | +---------------------> [38:30] L1 index 89 | +-------------------------------> [47:39] L0 index (not used) 90 +-------------------------------------------------> [63] TTBR0/1 91 92 93Translation table lookup with 64KB pages: 94 95+--------+--------+--------+--------+--------+--------+--------+--------+ 96|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| 97+--------+--------+--------+--------+--------+--------+--------+--------+ 98 | | | | | 99 | | | | v 100 | | | | [15:0] in-page offset 101 | | | +----------> [28:16] L3 index 102 | | +--------------------------> [41:29] L2 index (only 38:29 used) 103 | +-------------------------------> [47:42] L1 index (not used) 104 +-------------------------------------------------> [63] TTBR0/1 105