projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 1da177e4 LT |
1 | Kernel Memory Layout on ARM Linux |
| 2 | ||
| 3 | Russell King <rmk@arm.linux.org.uk> | |
| 02b30839 | 4 | November 17, 2005 (2.6.15) |
| 1da177e4 LT |
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 | ffff1000 ffff7fff Reserved. | |
| 25 | Platforms must not use this address range. | |
| 26 | ||
| 27 | ffff0000 ffff0fff CPU vector page. | |
| 28 | The CPU vectors are mapped here if the | |
| 29 | CPU supports vector relocation (control | |
| 30 | register V bit.) | |
| 31 | ||
| 5f0fbf9e NP |
32 | fffe0000 fffeffff XScale cache flush area. This is used |
| 33 | in proc-xscale.S to flush the whole data | |
| 34 | cache. Free for other usage on non-XScale. | |
| 35 | ||
| 36 | fff00000 fffdffff Fixmap mapping region. Addresses provided | |
| 37 | by fix_to_virt() will be located here. | |
| 38 | ||
| 39 | ffc00000 ffefffff DMA memory mapping region. Memory returned | |
| 1da177e4 LT |
40 | by the dma_alloc_xxx functions will be |
| 41 | dynamically mapped here. | |
| 42 | ||
| 43 | ff000000 ffbfffff Reserved for future expansion of DMA | |
| 44 | mapping region. | |
| 45 | ||
| 46 | VMALLOC_END feffffff Free for platform use, recommended. | |
| 02b30839 RK |
47 | VMALLOC_END must be aligned to a 2MB |
| 48 | boundary. | |
| 1da177e4 LT |
49 | |
| 50 | VMALLOC_START VMALLOC_END-1 vmalloc() / ioremap() space. | |
| 51 | Memory returned by vmalloc/ioremap will | |
| 52 | be dynamically placed in this region. | |
| 53 | VMALLOC_START may be based upon the value | |
| 54 | of the high_memory variable. | |
| 55 | ||
| 56 | PAGE_OFFSET high_memory-1 Kernel direct-mapped RAM region. | |
| 57 | This maps the platforms RAM, and typically | |
| 58 | maps all platform RAM in a 1:1 relationship. | |
| 59 | ||
| 60 | TASK_SIZE PAGE_OFFSET-1 Kernel module space | |
| 61 | Kernel modules inserted via insmod are | |
| 62 | placed here using dynamic mappings. | |
| 63 | ||
| 64 | 00001000 TASK_SIZE-1 User space mappings | |
| 65 | Per-thread mappings are placed here via | |
| 66 | the mmap() system call. | |
| 67 | ||
| 68 | 00000000 00000fff CPU vector page / null pointer trap | |
| 69 | CPUs which do not support vector remapping | |
| 70 | place their vector page here. NULL pointer | |
| 71 | dereferences by both the kernel and user | |
| 72 | space are also caught via this mapping. | |
| 73 | ||
| 74 | Please note that mappings which collide with the above areas may result | |
| 75 | in a non-bootable kernel, or may cause the kernel to (eventually) panic | |
| 76 | at run time. | |
| 77 | ||
| 78 | Since future CPUs may impact the kernel mapping layout, user programs | |
| 79 | must not access any memory which is not mapped inside their 0x0001000 | |
| 80 | to TASK_SIZE address range. If they wish to access these areas, they | |
| 81 | must set up their own mappings using open() and mmap(). |