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Diffstat (limited to 'Documentation/arm64/memory.txt')
| -rw-r--r-- | Documentation/arm64/memory.txt | 69 |
1 files changed, 26 insertions, 43 deletions
diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt index d50fa618371..344e85cc732 100644 --- a/Documentation/arm64/memory.txt +++ b/Documentation/arm64/memory.txt @@ -2,18 +2,18 @@ ============================== Author: Catalin Marinas <catalin.marinas@arm.com> -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. +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 63:39 set to 0 while the kernel addresses have +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. @@ -21,58 +21,40 @@ The swapper_pgd_dir address is written to TTBR1 and never written to TTBR0. -AArch64 Linux memory layout with 4KB pages: +AArch64 Linux memory layout with 4KB pages + 3 levels: Start End Size Use ----------------------------------------------------------------------- 0000000000000000 0000007fffffffff 512GB user +ffffff8000000000 ffffffffffffffff 512GB kernel -ffffff8000000000 ffffffbbfffeffff ~240GB vmalloc -ffffffbbffff0000 ffffffbbffffffff 64KB [guard page] +AArch64 Linux memory layout with 4KB pages + 4 levels: -ffffffbc00000000 ffffffbdffffffff 8GB vmemmap - -ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap] - -ffffffbffa000000 ffffffbffaffffff 16MB PCI I/O space - -ffffffbffb000000 ffffffbffbbfffff 12MB [guard] - -ffffffbffbc00000 ffffffbffbdfffff 2MB fixed mappings - -ffffffbffbe00000 ffffffbffbffffff 2MB [guard] - -ffffffbffc000000 ffffffbfffffffff 64MB modules - -ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map +Start End Size Use +----------------------------------------------------------------------- +0000000000000000 0000ffffffffffff 256TB user +ffff000000000000 ffffffffffffffff 256TB kernel -AArch64 Linux memory layout with 64KB pages: +AArch64 Linux memory layout with 64KB pages + 2 levels: Start End Size Use ----------------------------------------------------------------------- 0000000000000000 000003ffffffffff 4TB user +fffffc0000000000 ffffffffffffffff 4TB kernel -fffffc0000000000 fffffdfbfffeffff ~2TB vmalloc -fffffdfbffff0000 fffffdfbffffffff 64KB [guard page] +AArch64 Linux memory layout with 64KB pages + 3 levels: -fffffdfc00000000 fffffdfdffffffff 8GB vmemmap - -fffffdfe00000000 fffffdfffbbfffff ~8GB [guard, future vmmemap] - -fffffdfffa000000 fffffdfffaffffff 16MB PCI I/O space - -fffffdfffb000000 fffffdfffbbfffff 12MB [guard] - -fffffdfffbc00000 fffffdfffbdfffff 2MB fixed mappings - -fffffdfffbe00000 fffffdfffbffffff 2MB [guard] +Start End Size Use +----------------------------------------------------------------------- +0000000000000000 0000ffffffffffff 256TB user +ffff000000000000 ffffffffffffffff 256TB kernel -fffffdfffc000000 fffffdffffffffff 64MB modules -fffffe0000000000 ffffffffffffffff 2TB kernel logical memory map +For details of the virtual kernel memory layout please see the kernel +booting log. Translation table lookup with 4KB pages: @@ -86,7 +68,7 @@ Translation table lookup with 4KB pages: | | | | +-> [20:12] L3 index | | | +-----------> [29:21] L2 index | | +---------------------> [38:30] L1 index - | +-------------------------------> [47:39] L0 index (not used) + | +-------------------------------> [47:39] L0 index +-------------------------------------------------> [63] TTBR0/1 @@ -99,10 +81,11 @@ Translation table lookup with 64KB pages: | | | | v | | | | [15:0] in-page offset | | | +----------> [28:16] L3 index - | | +--------------------------> [41:29] L2 index (only 38:29 used) - | +-------------------------------> [47:42] L1 index (not used) + | | +--------------------------> [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): |