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1=================================2Kernel Memory Layout on ARM Linux3=================================4 5 Russell King <rmk@arm.linux.org.uk>6 7 November 17, 2005 (2.6.15)8 9This document describes the virtual memory layout which the Linux10kernel uses for ARM processors. It indicates which regions are11free for platforms to use, and which are used by generic code.12 13The ARM CPU is capable of addressing a maximum of 4GB virtual memory14space, and this must be shared between user space processes, the15kernel, and hardware devices.16 17As the ARM architecture matures, it becomes necessary to reserve18certain regions of VM space for use for new facilities; therefore19this document may reserve more VM space over time.20 21=============== =============== ===============================================22Start End Use23=============== =============== ===============================================24ffff8000 ffffffff copy_user_page / clear_user_page use.25 For SA11xx and Xscale, this is used to26 setup a minicache mapping.27 28ffff4000 ffffffff cache aliasing on ARMv6 and later CPUs.29 30ffff1000 ffff7fff Reserved.31 Platforms must not use this address range.32 33ffff0000 ffff0fff CPU vector page.34 The CPU vectors are mapped here if the35 CPU supports vector relocation (control36 register V bit.)37 38fffe0000 fffeffff XScale cache flush area. This is used39 in proc-xscale.S to flush the whole data40 cache. (XScale does not have TCM.)41 42fffe8000 fffeffff DTCM mapping area for platforms with43 DTCM mounted inside the CPU.44 45fffe0000 fffe7fff ITCM mapping area for platforms with46 ITCM mounted inside the CPU.47 48ffc80000 ffefffff Fixmap mapping region. Addresses provided49 by fix_to_virt() will be located here.50 51ffc00000 ffc7ffff Guard region52 53ff800000 ffbfffff Permanent, fixed read-only mapping of the54 firmware provided DT blob55 56fee00000 feffffff Mapping of PCI I/O space. This is a static57 mapping within the vmalloc space.58 59VMALLOC_START VMALLOC_END-1 vmalloc() / ioremap() space.60 Memory returned by vmalloc/ioremap will61 be dynamically placed in this region.62 Machine specific static mappings are also63 located here through iotable_init().64 VMALLOC_START is based upon the value65 of the high_memory variable, and VMALLOC_END66 is equal to 0xff800000.67 68PAGE_OFFSET high_memory-1 Kernel direct-mapped RAM region.69 This maps the platforms RAM, and typically70 maps all platform RAM in a 1:1 relationship.71 72PKMAP_BASE PAGE_OFFSET-1 Permanent kernel mappings73 One way of mapping HIGHMEM pages into kernel74 space.75 76MODULES_VADDR MODULES_END-1 Kernel module space77 Kernel modules inserted via insmod are78 placed here using dynamic mappings.79 80TASK_SIZE MODULES_VADDR-1 KASAn shadow memory when KASan is in use.81 The range from MODULES_VADDR to the top82 of the memory is shadowed here with 1 bit83 per byte of memory.84 8500001000 TASK_SIZE-1 User space mappings86 Per-thread mappings are placed here via87 the mmap() system call.88 8900000000 00000fff CPU vector page / null pointer trap90 CPUs which do not support vector remapping91 place their vector page here. NULL pointer92 dereferences by both the kernel and user93 space are also caught via this mapping.94=============== =============== ===============================================95 96Please note that mappings which collide with the above areas may result97in a non-bootable kernel, or may cause the kernel to (eventually) panic98at run time.99 100Since future CPUs may impact the kernel mapping layout, user programs101must not access any memory which is not mapped inside their 0x0001000102to TASK_SIZE address range. If they wish to access these areas, they103must set up their own mappings using open() and mmap().104