AArch64 Linux uses either 3 levels or 4 levels of translation tables with the 4KB page configuration, allowing 39-bit (512GB) or 48-bit (256TB) virtual addresses, respectively, for both user and kernel. With 64KB pages, only 2 levels of translation tables, allowing 42-bit (4TB) virtual address, are used but the memory layout is the same. User addresses have bits 63:48 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_pg_dir address is written to TTBR1 and never written to TTBR0. AArch64 Linux memory layout with 4KB pages + 3 levels: Start End Size Use ----------------------------------------------------------------------- 0000000000000000 0000007fffffffff 512GB user ffffff8000000000 ffffffffffffffff 512GB kernel AArch64 Linux memory layout with 4KB pages + 4 levels: Start End Size Use ----------------------------------------------------------------------- 0000000000000000 0000ffffffffffff 256TB user ffff000000000000 ffffffffffffffff 256TB kernel AArch64 Linux memory layout with 64KB pages + 2 levels: Start End Size Use ----------------------------------------------------------------------- 0000000000000000 000003ffffffffff 4TB user fffffc0000000000 ffffffffffffffff 4TB kernel AArch64 Linux memory layout with 64KB pages + 3 levels: Start End Size Use ----------------------------------------------------------------------- 0000000000000000 0000ffffffffffff 256TB user ffff000000000000 ffffffffffffffff 256TB kernel For details of the virtual kernel memory layout please see the kernel booting log. 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 +-------------------------------------------------> [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 | +-------------------------------> [47:42] L1 index +-------------------------------------------------> [63] TTBR0/1