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-rw-r--r--Documentation/arm64/memory.txt69
1 files changed, 26 insertions, 43 deletions
diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt
index d50fa618371b..344e85cc7323 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):