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!

Coaptation

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.

Willie

Thank you very much! The reference is very useful! It's like the page table entry at the 4 levels page table. So I guess the offset of the PML table is A12-A20? – Coaptation