What is PML4 short for?

Question

In Xen code ./xen/include/asm-x86/config.h, I saw the memory layout code is:

/*
137  * Meng: Xen-definitive guide: P81
138  * Memory layout:
139  *  0x0000000000000000 - 0x00007fffffffffff [128TB, 2^47 bytes, PML4:0-255]
140  *    Guest-defined use (see below for compatibility mode guests).
141  *  0x0000800000000000 - 0xffff7fffffffffff [16EB]
142  *    Inaccessible: current arch only supports 48-bit sign-extended VAs.
143  *  0xffff800000000000 - 0xffff803fffffffff [256GB, 2^38 bytes, PML4:256]

I'm very confused at what the PML4 is short for. I did know that the x86_64 only uses 48 bits out of 64bits. But what is the PML4 short for? It may help me understand the number behind it.

Thanks!

Answer 1

It's short for Page Map Level 4. A bit of explanation can be found here. Basically it's just the way AMD decided to label page tables.