aboutsummaryrefslogtreecommitdiff
path: root/Documentation/arm64
diff options
context:
space:
mode:
authorCatalin Marinas <catalin.marinas@arm.com>2012-03-05 11:49:27 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2012-09-17 13:41:56 +0100
commit4f04d8f00545110a0e525ae2fb62ab38cb417236 (patch)
tree021c6ff01a972de47341959b0bd0888775c9ed7b /Documentation/arm64
parent60ffc30d5652810dd34ea2eec41504222f5d5791 (diff)
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 <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Tony Lindgren <tony@atomide.com> Acked-by: Nicolas Pitre <nico@linaro.org> Acked-by: Olof Johansson <olof@lixom.net> Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com> Acked-by: Arnd Bergmann <arnd@arndb.de>
Diffstat (limited to 'Documentation/arm64')
-rw-r--r--Documentation/arm64/memory.txt73
1 files changed, 73 insertions, 0 deletions
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 <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.
+
+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