Understanding the kernel architecture – part 1
In this section, we begin to deepen our understanding of the Linux kernel. More specifically, here, we delve into what user and kernel spaces are, and the major subsystems and various components that make up the kernel. This information is dealt with at a higher level of abstraction for now and is deliberately kept brief. We shall delve a lot deeper into understanding the fabric of the kernel in Chapter 6, Kernel Internals Essentials – Processes and Threads.
User space and kernel space
Modern microprocessors support code execution at a minimum of two privilege levels. As a real-world example, the Intel/AMD x86[-64] family supports four privilege levels (they call them ring levels), the AArch32 (ARM-32) microprocessor family supports up to seven modes (ARM calls them execution modes; six are privileged and one is non-privileged), and the AArch64 (ARM-64/ARMv8) microprocessor family supports four exception levels ...
