Commit 85a3bd41 authored by Changbin Du's avatar Changbin Du Committed by Jonathan Corbet
Browse files

Documentation: x86: convert x86_64/5level-paging.txt to reST 



This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.

Signed-off-by: default avatarChangbin Du <changbin.du@gmail.com>
Reviewed-by: default avatarMauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent b88679d2

Documentation/x86/x86_64/5level-paging.txt→Documentation/x86/x86_64/5level-paging.rst

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== Overview ==

.. SPDX-License-Identifier: GPL-2.0



==============

5-level paging

==============



Overview

========

Original x86-64 was limited by 4-level paing to 256 TiB of virtual address

space and 64 TiB of physical address space. We are already bumping into

this limit: some vendors offers servers with 64 TiB of memory today.
@@ -16,16 +22,17 @@ QEMU 2.9 and later support 5-level paging. 
Virtual memory layout for 5-level paging is described in

Documentation/x86/x86_64/mm.txt



== Enabling 5-level paging ==



Enabling 5-level paging

=======================

CONFIG_X86_5LEVEL=y enables the feature.



Kernel with CONFIG_X86_5LEVEL=y still able to boot on 4-level hardware.

In this case additional page table level -- p4d -- will be folded at

runtime.



== User-space and large virtual address space ==



User-space and large virtual address space

==========================================

On x86, 5-level paging enables 56-bit userspace virtual address space.

Not all user space is ready to handle wide addresses. It's known that

at least some JIT compilers use higher bits in pointers to encode their
@@ -58,4 +65,3 @@ One important case we need to handle here is interaction with MPX. 
MPX (without MAWA extension) cannot handle addresses above 47-bit, so we

need to make sure that MPX cannot be enabled we already have VMA above

the boundary and forbid creating such VMAs once MPX is enabled.

Documentation/x86/x86_64/index.rst

+1 −0
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@@ -10,3 +10,4 @@ x86_64 Support 
   boot-options

   uefi

   mm

   5level-paging