Linux Device Drivers Development

System memory layout – kernel space and user space

Throughout this chapter, terms such as kernel space and user space will refer to their virtual address space. On Linux systems, each process owns a virtual address space. It is a kind of memory sandbox during the life of the process. That address space is 4 GB in size on 32-bit systems (even on a system with physical memory less than 4 GB). For each process, that 4 GB address space is split into two parts:

• User space virtual addresses
• Kernel space virtual addresses

The way the split is done depends on a special kernel configuration option, CONFIG_PAGE_OFFSET, which defines where the kernel addresses section starts in a process address space. The common value is 0xC0000000 by default on ...