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| -rw-r--r-- | Documentation/arm64/memory.txt | 59 |
1 files changed, 51 insertions, 8 deletions
diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt index d50fa61..4c720d6 100644 --- a/Documentation/arm64/memory.txt +++ b/Documentation/arm64/memory.txt @@ -8,10 +8,11 @@ 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 the same bits set to 1. TTBRx selection is given by bit 63 of the @@ -21,7 +22,7 @@ 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 ----------------------------------------------------------------------- @@ -48,7 +49,34 @@ ffffffbffc000000 ffffffbfffffffff 64MB modules ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map -AArch64 Linux memory layout with 64KB pages: +AArch64 Linux memory layout with 4KB pages + 4 levels: + +Start End Size Use +----------------------------------------------------------------------- +0000000000000000 0000ffffffffffff 256TB user + +ffff000000000000 ffff7bfffffeffff ~124TB vmalloc + +ffff7bffffff0000 ffff7bffffffffff 64KB [guard page] + +ffff7c0000000000 ffff7dffffffffff 2TB vmemmap + +ffff7e0000000000 ffff7ffffbbfffff ~2TB [guard, future vmmemap] + +ffff7ffffa000000 ffff7ffffaffffff 16MB PCI I/O space + +ffff7ffffb000000 ffff7ffffbbfffff 12MB [guard] + +ffff7ffffbc00000 ffff7ffffbdfffff 2MB fixed mappings + +ffff7ffffbe00000 ffff7ffffbffffff 2MB [guard] + +ffff7ffffc000000 ffff7fffffffffff 64MB modules + +ffff800000000000 ffffffffffffffff 128TB kernel logical memory map + + +AArch64 Linux memory layout with 64KB pages + 2 levels: Start End Size Use ----------------------------------------------------------------------- @@ -75,7 +103,7 @@ fffffdfffc000000 fffffdffffffffff 64MB modules fffffe0000000000 ffffffffffffffff 2TB kernel logical memory map -Translation table lookup with 4KB pages: +Translation table lookup with 4KB pages + 3 levels: +--------+--------+--------+--------+--------+--------+--------+--------+ |63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| @@ -90,7 +118,22 @@ Translation table lookup with 4KB pages: +-------------------------------------------------> [63] TTBR0/1 -Translation table lookup with 64KB pages: +Translation table lookup with 4KB pages + 4 levels: + ++--------+--------+--------+--------+--------+--------+--------+--------+ +|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 + 2 levels: +--------+--------+--------+--------+--------+--------+--------+--------+ |63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| |
