In x64, addresses have 64 bits, but just the 48 less significant ones are used. The first 9 bits of these 48 bits are the offset of the page global director. Let's say I have 2 processes P and Q. Are P and Q "associated" to one and one only of these 2^9 page global directors?

In other words, I'm wondering if a process can access multiple page global directors.

According to me, the answer is YES because the address of the page global director is contained in the CR3 register and the offset of 9 bits is used to pick one among the 2^9 page UPPER directors, but I don't know if I am correct.

@Curio take a look at the largest processes on your system, /proc/${pid}/maps should show you addresses whose most significant nine bits (inside the 48) are different, which answers your question if I’ve understood it correctly.

Perfect. As a result, I imagine that we can't have 2^9 processes at the same time, otherwise, there would be 2 processes with the same page global director.

@Curio each process has its own page directory, and the value of CR3 changes every time the context switches (and when jumping to the kernel, with KPTI).

Perfect. Thank you so much.