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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 without the Virtualization Host Extensions, the
-hypervisor maps kernel pages in EL2 at a fixed (and potentially
-random) offset from the linear mapping. See the kern_hyp_va macro and
-kvm_update_va_mask function for more details. MMIO devices such as
-GICv2 gets mapped next to the HYP idmap page, as do vectors when
-ARM64_HARDEN_EL2_VECTORS is selected for particular CPUs.
-
-When using KVM with the Virtualization Host Extensions, no additional
-mappings are created, since the host kernel runs directly in EL2.