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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.
+
+ffc00000        ffefffff        Fixmap mapping region.  Addresses provided
+                                by fix_to_virt() will be located here.
+
+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.
+
+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().