Kernel Memory Layout on ARM Linux

jiok

Kernel Memory Layout on ARM Linux
  Russell King
       November 17, 2005 (2.6.15)
这个文档描述了linux内核对于arm的虚拟内存,这表明哪些区域是自由的使用对于这个平台,并且哪些是被一般的代码使用的.
ARM能支持4G的VM,这是共享的在有用户空间,内核和设备空间.
随着ARM体系的成熟,这是必要的去保留一定的VM区域为新的设备的使用,因此随意时间的过去这个文档可能保留更多的空间.
Start  End  Use
--------------------------------------------------------------------------
ffff8000 ffffffff copy_user_page / clear_user_page use.
    For SA11xx and Xscale, this is used to
    setup a minicache mapping.
//作为copy_user_page / clear_user_page使用.对于SA11xx and Xscale,这用于设备为小型cache的映像.
ffff1000 ffff7fff Reserved.
    Platforms must not use this address range.
//保留
ffff0000 ffff0fff CPU vector page.
    The CPU vectors are mapped here if the
    CPU supports vector relocation (control
    register V bit.)
//CPU vector page.如果CPU支持向量重置(控制寄存器的V位),CPU向量就映象到这里.
ffc00000 fffeffff DMA memory mapping region.  Memory returned
    by the dma_alloc_xxx functions will be
    dynamically mapped here.
//DMA内存的映象区域,dma_alloc_xxx函数将会动态的分配到这里.
ff000000 ffbfffff Reserved for future expansion of DMA
    mapping region.
//保留为将来DMA的扩展.
VMALLOC_END feffffff Free for platform use, recommended.
    VMALLOC_END must be aligned to a 2MB
    boundary.
//自由使用,被推荐.VMALLOC_END 必须对齐2M的边界.
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.
//vmalloc() / ioremap() space.这两个函数动态分配的区域.
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.
//内核直接映象的RAM区域.
TASK_SIZE PAGE_OFFSET-1 Kernel module space
    Kernel modules inserted via insmod are
    placed here using dynamic mappings.
//内核.模块空间.
00001000 TASK_SIZE-1 User space mappings
    Per-thread mappings are placed here via
    the mmap() system call.
//用户空间
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.
CPU向量页/空指针陷阱.
(注:里面的宏已定义)
请注意上面区域的冲突映象可能导致不能启动内核,OR导致死机(如里系统在运行).
由于将来CPU可能影响内核映象层,用户程序不应该去访问没有被映象在0x0001000
to TASK_SIZE的范围内的内存,如果想去访问这区域,那么要设置它们自己的映象
用 open() and mmap().

本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u/22485/showart_163818.html