Documentation/arch/arm/memory.rst

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=================================
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.

ffc80000	ffefffff	Fixmap mapping region.  Addresses provided
				by fix_to_virt() will be located here.

ffc00000	ffc7ffff	Guard region

ff800000	ffbfffff	Permanent, fixed read-only mapping of the
				firmware provided DT blob

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 0xff800000.

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.

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