Memory Layout on AArch64 Linux ============================== Author: Catalin Marinas 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 ffffffbbfffcffff ~240GB vmalloc ffffffbbfffd0000 ffffffbcfffdffff 64KB [guard page] ffffffbbfffe0000 ffffffbcfffeffff 64KB PCI I/O space ffffffbbffff0000 ffffffbcffffffff 64KB [guard page] ffffffbc00000000 ffffffbdffffffff 8GB vmemmap ffffffbe00000000 ffffffbffbffffff ~8GB [guard, future vmmemap] ffffffbffc000000 ffffffbfffffffff 64MB modules ffffffc000000000 ffffffffffffffff 256GB memory 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