Kernel Memory Layout on ARM Linux
  
  		Russell King <rmk@arm.linux.org.uk>

  		     November 17, 2005 (2.6.15)

  
  This document describes the virtual memory layout which the Linux
  kernel uses for ARM processors.  It indicates which regions are
  free for platforms to use, and which are used by generic code.
  
  The ARM CPU is capable of addressing a maximum of 4GB virtual memory
  space, and this must be shared between user space processes, the
  kernel, and hardware devices.
  
  As the ARM architecture matures, it becomes necessary to reserve
  certain regions of VM space for use for new facilities; therefore
  this document may reserve more VM space over time.
  
  Start		End		Use
  --------------------------------------------------------------------------
  ffff8000	ffffffff	copy_user_page / clear_user_page use.
  				For SA11xx and Xscale, this is used to
  				setup a minicache mapping.

  ffff4000	ffffffff	cache aliasing on ARMv6 and later CPUs.

  ffff1000	ffff7fff	Reserved.
  				Platforms must not use this address range.
  
  ffff0000	ffff0fff	CPU vector page.
  				The CPU vectors are mapped here if the
  				CPU supports vector relocation (control
  				register V bit.)

  fffe0000	fffeffff	XScale cache flush area.  This is used
  				in proc-xscale.S to flush the whole data

  				cache. (XScale does not have TCM.)
  
  fffe8000	fffeffff	DTCM mapping area for platforms with
  				DTCM mounted inside the CPU.
  
  fffe0000	fffe7fff	ITCM mapping area for platforms with
  				ITCM mounted inside the CPU.

  
  fff00000	fffdffff	Fixmap mapping region.  Addresses provided
  				by fix_to_virt() will be located here.
  
  ffc00000	ffefffff	DMA memory mapping region.  Memory returned

  				by the dma_alloc_xxx functions will be
  				dynamically mapped here.
  
  ff000000	ffbfffff	Reserved for future expansion of DMA
  				mapping region.

  fee00000	feffffff	Mapping of PCI I/O space. This is a static
  				mapping within the vmalloc space.

  VMALLOC_START	VMALLOC_END-1	vmalloc() / ioremap() space.
  				Memory returned by vmalloc/ioremap will
  				be dynamically placed in this region.

  				Machine specific static mappings are also
  				located here through iotable_init().
  				VMALLOC_START is based upon the value
  				of the high_memory variable, and VMALLOC_END
  				is equal to 0xff000000.

  
  PAGE_OFFSET	high_memory-1	Kernel direct-mapped RAM region.
  				This maps the platforms RAM, and typically
  				maps all platform RAM in a 1:1 relationship.

  PKMAP_BASE	PAGE_OFFSET-1	Permanent kernel mappings
  				One way of mapping HIGHMEM pages into kernel
  				space.
  
  MODULES_VADDR	MODULES_END-1	Kernel module space

  				Kernel modules inserted via insmod are
  				placed here using dynamic mappings.
  
  00001000	TASK_SIZE-1	User space mappings
  				Per-thread mappings are placed here via
  				the mmap() system call.
  
  00000000	00000fff	CPU vector page / null pointer trap
  				CPUs which do not support vector remapping
  				place their vector page here.  NULL pointer
  				dereferences by both the kernel and user
  				space are also caught via this mapping.
  
  Please note that mappings which collide with the above areas may result
  in a non-bootable kernel, or may cause the kernel to (eventually) panic
  at run time.
  
  Since future CPUs may impact the kernel mapping layout, user programs
  must not access any memory which is not mapped inside their 0x0001000
  to TASK_SIZE address range.  If they wish to access these areas, they
  must set up their own mappings using open() and mmap().