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- 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
|
