| Memory Layout on AArch64 Linux |
| ============================== |
| |
| Author: Catalin Marinas <catalin.marinas@arm.com> |
| |
| 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 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 |
| |
| |
| 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 |
