1 Kernel Memory Layout on ARM Linux
3 Russell King <rmk@arm.linux.org.uk>
4 April 27, 2003 (2.5.68)
6 This document describes the virtual memory layout which the Linux
7 kernel uses for ARM processors. It indicates which regions are
8 free for platforms to use, and which are used by generic code.
10 The ARM CPU is capable of addressing a maximum of 4GB virtual memory
11 space, and this must be shared between user space processes, the
12 kernel, and hardware devices.
14 As the ARM architecture matures, it becomes necessary to reserve
15 certain regions of VM space for use for new facilities; therefore
16 this document may reserve more VM space over time.
19 --------------------------------------------------------------------------
20 ffff8000 ffffffff copy_user_page / clear_user_page use.
21 For SA11xx and Xscale, this is used to
22 setup a minicache mapping.
24 ffff1000 ffff7fff Reserved.
25 Platforms must not use this address range.
27 ffff0000 ffff0fff CPU vector page.
28 The CPU vectors are mapped here if the
29 CPU supports vector relocation (control
32 ffe00000 fffeffff Free for platform use, not recommended.
34 ffc00000 ffdfffff 2MB consistent memory mapping.
35 Memory returned by the consistent_alloc
36 low level function will be dynamically
39 ff000000 ffbfffff Free for platform use, not recommended.
41 VMALLOC_END ff000000 Free for platform use, recommended.
43 VMALLOC_START VMALLOC_END vmalloc() / ioremap() space.
44 Memory returned by vmalloc/ioremap will
45 be dynamically placed in this region.
46 VMALLOC_START may be based upon the value
47 of the high_memory variable.
49 PAGE_OFFSET high_memory Kernel direct-mapped RAM region.
50 This maps the platforms RAM, and typically
51 maps all platform RAM in a 1:1 relationship.
53 TASK_SIZE PAGE_OFFSET Kernel module space
54 Kernel modules inserted via insmod are
55 placed here using dynamic mappings.
57 00001000 TASK_SIZE User space mappings
58 Per-thread mappings are placed here via
59 the mmap() system call.
61 00000000 00000fff CPU vector page / null pointer trap
62 CPUs which do not support vector remapping
63 place their vector page here. NULL pointer
64 dereferences by both the kernel and user
65 space are also caught via this mapping.
67 Please note that mappings which collide with the above areas may result
68 in a non-bootable kernel, or may cause the kernel to (eventually) panic
71 Since future CPUs may impact the kernel mapping layout, user programs
72 must not access any memory which is not mapped inside their 0x0001000
73 to TASK_SIZE address range. If they wish to access these areas, they
74 must set up their own mappings using open() and mmap().