[sophacles]

But they don't directly access memory. They access an address that may be translatable by the mmu to a physical location in ram. They may also write to an address that the kernel hasn't allocated a page for yet, but that the kernel has agreed to map into the process' memory. In this case the kernel handles the trap and maps a page of actual ram (etc) and then the process continues forward progress.

[vbezhenar]

That's just the way CPU works. It has nothing to do with kernel or userspace. Kernel code will behave identically.