Learning about Meltdown - confused about one thing

From Meltdown's Wikipedia article :

>Since many operating systems map physical memory, kernel processes, and other running user space processes into the address space of every process, Meltdown effectively makes it possible for a rogue process to read any physical, kernel or other processes' mapped memory – regardless of whether it should be able to do so. Defenses against Meltdown would require avoiding the use of memory mapping in a manner vulnerable to such exploits (i.e. a software-based solution) or …

address article cybersecurity effectively kernel map meltdown memory operating systems physical process processes rogue running space systems wikipedia