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Based on kernel version 3.2. Page generated on 2012-01-05 23:27 EST.

1			Kernel Memory Layout on ARM Linux
2	
3			Russell King <rmk@arm.linux.org.uk>
4			     November 17, 2005 (2.6.15)
5	
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.
9	
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.
13	
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.
17	
18	Start		End		Use
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.
23	
24	ffff4000	ffffffff	cache aliasing on ARMv6 and later CPUs.
25	
26	ffff1000	ffff7fff	Reserved.
27					Platforms must not use this address range.
28	
29	ffff0000	ffff0fff	CPU vector page.
30					The CPU vectors are mapped here if the
31					CPU supports vector relocation (control
32					register V bit.)
33	
34	fffe0000	fffeffff	XScale cache flush area.  This is used
35					in proc-xscale.S to flush the whole data
36					cache. (XScale does not have TCM.)
37	
38	fffe8000	fffeffff	DTCM mapping area for platforms with
39					DTCM mounted inside the CPU.
40	
41	fffe0000	fffe7fff	ITCM mapping area for platforms with
42					ITCM mounted inside the CPU.
43	
44	fff00000	fffdffff	Fixmap mapping region.  Addresses provided
45					by fix_to_virt() will be located here.
46	
47	ffc00000	ffefffff	DMA memory mapping region.  Memory returned
48					by the dma_alloc_xxx functions will be
49					dynamically mapped here.
50	
51	ff000000	ffbfffff	Reserved for future expansion of DMA
52					mapping region.
53	
54	VMALLOC_END	feffffff	Free for platform use, recommended.
55					VMALLOC_END must be aligned to a 2MB
56					boundary.
57	
58	VMALLOC_START	VMALLOC_END-1	vmalloc() / ioremap() space.
59					Memory returned by vmalloc/ioremap will
60					be dynamically placed in this region.
61					VMALLOC_START may be based upon the value
62					of the high_memory variable.
63	
64	PAGE_OFFSET	high_memory-1	Kernel direct-mapped RAM region.
65					This maps the platforms RAM, and typically
66					maps all platform RAM in a 1:1 relationship.
67	
68	PKMAP_BASE	PAGE_OFFSET-1	Permanent kernel mappings
69					One way of mapping HIGHMEM pages into kernel
70					space.
71	
72	MODULES_VADDR	MODULES_END-1	Kernel module space
73					Kernel modules inserted via insmod are
74					placed here using dynamic mappings.
75	
76	00001000	TASK_SIZE-1	User space mappings
77					Per-thread mappings are placed here via
78					the mmap() system call.
79	
80	00000000	00000fff	CPU vector page / null pointer trap
81					CPUs which do not support vector remapping
82					place their vector page here.  NULL pointer
83					dereferences by both the kernel and user
84					space are also caught via this mapping.
85	
86	Please note that mappings which collide with the above areas may result
87	in a non-bootable kernel, or may cause the kernel to (eventually) panic
88	at run time.
89	
90	Since future CPUs may impact the kernel mapping layout, user programs
91	must not access any memory which is not mapped inside their 0x0001000
92	to TASK_SIZE address range.  If they wish to access these areas, they
93	must set up their own mappings using open() and mmap().
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