Once again, refer to Figure 7.1; it shows the actual process VAS layout for a single 32-bit process. The reality, of course – and this is key – is that all processes alive on the system have their own unique user-mode VAS but share the same kernel segment. For some contrast from Figure 7.1, which showed a 2:2 (GB) VM split, the following figure shows the actual situation for a typical IA-32 system, with a 3:1 (GB) VM split:
Notice in the preceding figure how the address space reflects a 3:1 (GB) VM split. The user address space extends from 0 to 0xbfff ffff (0xc000 0000 is the 3 GB mark; this is what the PAGE_OFFSET macro is set to), and the kernel VAS extends from 0xc000 0000 (3 GB) to 0xffff ffff (4 GB).
Later in this chapter, we will cover the...
