Commit ea0765e8 authored by Changbin Du's avatar Changbin Du Committed by Jonathan Corbet
Browse files

Documentation: x86: convert pti.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 0c7180f2

Documentation/x86/index.rst

+1 −0
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@@ -21,3 +21,4 @@ x86-specific Documentation 
   protection-keys

   intel_mpx

   amd-memory-encryption

   pti

Documentation/x86/pti.txt→Documentation/x86/pti.rst

+13 −4
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.. SPDX-License-Identifier: GPL-2.0



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

Page Table Isolation (PTI)

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



Overview

========



Page Table Isolation (pti, previously known as KAISER[1]) is a

Page Table Isolation (pti, previously known as KAISER [1]_) is a

countermeasure against attacks on the shared user/kernel address

space such as the "Meltdown" approach[2].

space such as the "Meltdown" approach [2]_.



To mitigate this class of attacks, we create an independent set of

page tables for use only when running userspace applications.  When
@@ -60,6 +66,7 @@ Protection against side-channel attacks is important. But, 
this protection comes at a cost:



1. Increased Memory Use



  a. Each process now needs an order-1 PGD instead of order-0.

     (Consumes an additional 4k per process).

  b. The 'cpu_entry_area' structure must be 2MB in size and 2MB
@@ -68,6 +75,7 @@ this protection comes at a cost: 
     is decompressed, but no space in the kernel image itself.



2. Runtime Cost



  a. CR3 manipulation to switch between the page table copies

     must be done at interrupt, syscall, and exception entry

     and exit (it can be skipped when the kernel is interrupted,
@@ -142,6 +150,7 @@ ideally doing all of these in parallel: 
   interrupted, including nested NMIs.  Using "-c" boosts the rate of

   NMIs, and using two -c with separate counters encourages nested NMIs

   and less deterministic behavior.

   ::



	while true; do perf record -c 10000 -e instructions,cycles -a sleep 10; done
@@ -182,5 +191,5 @@ that are worth noting here. 
   tended to be TLB invalidation issues.  Usually invalidating

   the wrong PCID, or otherwise missing an invalidation.



1. https://gruss.cc/files/kaiser.pdf

2. https://meltdownattack.com/meltdown.pdf
 
.. [1] https://gruss.cc/files/kaiser.pdf

.. [2] https://meltdownattack.com/meltdown.pdf