why kernel needs virtual addressing?

Question

In Linux each process has its virtual address space (e.g. 4 GB in case of 32 bit system, wherein 3GB is reserved for process and 1 GB for kernel). This virtual addressing mechan

Answer 1

Virtual Memory Management is that feature of Linux which enables Multi-tasking in system without any limitation on no. of task or amount of memory used by each task. The Linux Memory Manager Subsystem (along with MMU hardware) facilitates VMM support, where memory or mem-mapped device are accessed through virtual addresses. Within Linux everything, both kernel and user components, works with virtual address except when dealing with real hardware. That's when the Memory Manager takes its place, does virtual-to-physical address translation and points to physical mem/dev location.

A process is an abstract entity, defined by kernel to which system resources are allocated in order to execute a program. In Linux Process Management the kernel is an integrated part of a process memory map. A process has two main regions, like two faces of one coin:

• User Space view - contains user program sections (Code, Data, Stack, Heap, etc...) used by process

• Kernel Space view - contains kernel data structures that maintain information (PID. States, FD, Resource Usage, etc...) about the process

  

Every process in Linux system has a unique and separate User Space Region. This feature of Linux VMM isolates each process program sections from one and other. But all processes in the system shares the common Kernel Space Region. When a process needs service from the kernel it must execute the kernel code in this region, or in other words kernel is performing on behalf of user process request.