From 4f04d8f00545110a0e525ae2fb62ab38cb417236 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Mon, 5 Mar 2012 11:49:27 +0000 Subject: arm64: MMU definitions The virtual memory layout is described in Documentation/arm64/memory.txt. This patch adds the MMU definitions for the 4KB and 64KB translation table configurations. The SECTION_SIZE is 2MB with 4KB page and 512MB with 64KB page configuration. PHYS_OFFSET is calculated at run-time and stored in a variable (no run-time code patching at this stage). On the current implementation, both user and kernel address spaces are 512G (39-bit) each with a maximum of 256G for the RAM linear mapping. Linux uses 3 levels of translation tables with the 4K page configuration and 2 levels with the 64K configuration. Extending the memory space beyond 39-bit with the 4K pages or 42-bit with 64K pages requires an additional level of translation tables. The SPARSEMEM configuration is global to all AArch64 platforms and allows for 1GB sections with SPARSEMEM_VMEMMAP enabled by default. Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas Acked-by: Tony Lindgren Acked-by: Nicolas Pitre Acked-by: Olof Johansson Acked-by: Santosh Shilimkar Acked-by: Arnd Bergmann --- Documentation/arm64/memory.txt | 73 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 Documentation/arm64/memory.txt (limited to 'Documentation') diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt new file mode 100644 index 00000000000..dbbdcbba75a --- /dev/null +++ b/Documentation/arm64/memory.txt @@ -0,0 +1,73 @@ + Memory Layout on AArch64 Linux + ============================== + +Author: Catalin Marinas +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. + +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 +virtual address. The swapper_pg_dir contains only kernel (global) +mappings while the user pgd contains only user (non-global) mappings. +The swapper_pgd_dir address is written to TTBR1 and never written to +TTBR0. + + +AArch64 Linux memory layout: + +Start End Size Use +----------------------------------------------------------------------- +0000000000000000 0000007fffffffff 512GB user + +ffffff8000000000 ffffffbbfffcffff ~240GB vmalloc + +ffffffbbfffd0000 ffffffbcfffdffff 64KB [guard page] + +ffffffbbfffe0000 ffffffbcfffeffff 64KB PCI I/O space + +ffffffbbffff0000 ffffffbcffffffff 64KB [guard page] + +ffffffbc00000000 ffffffbdffffffff 8GB vmemmap + +ffffffbe00000000 ffffffbffbffffff ~8GB [guard, future vmmemap] + +ffffffbffc000000 ffffffbfffffffff 64MB modules + +ffffffc000000000 ffffffffffffffff 256GB memory + + +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 (not used) + +-------------------------------------------------> [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 (only 38:29 used) + | +-------------------------------> [47:42] L1 index (not used) + +-------------------------------------------------> [63] TTBR0/1 -- cgit v1.2.3