ARM linux内核在内存中的布局

Kernel Memory Layout on ARM Linux

Russell King

     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.

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.)

ffc00000 fffeffff 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.

VMALLOC_END feffffff Free for platform use, recommended.

VMALLOC_END must be aligned to a 2MB

boundary.

VMALLOC_START VMALLOC_END-1 vmalloc() / ioremap() space.

Memory returned by vmalloc/ioremap will

be dynamically placed in this region.

VMALLOC_START may be based upon the value

of the high_memory variable.

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.

TASK_SIZE PAGE_OFFSET-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().