Examining the kernel VAS
As we have talked about in the preceding chapter, and as seen in Figure 7.7, it’s critical to understand that all processes have their own unique user VAS but share the kernel space – what we call the kernel segment or kernel VAS. Let’s begin this section by starting to examine some common (arch-independent) regions of the kernel VAS.
The kernel VAS’s memory layout is very arch (CPU)-dependent. Nevertheless, all architectures share some commonalities. The following basic diagram represents both the user VAS and the kernel VAS (in a horizontally tiled format), as seen on a typical x86_32 (or IA-32) with a 3:1 (GB) VM split:
Figure 7.12: User and kernel VASs on an x86_32 with a 3:1 (GB) VM split with a focus on the lowmem region; this figure is deliberately simplistic
Let’s go over each region of the process VAS (from left to right, as seen in Figure 7.12):
