Commit 3d07bc39 authored by Changbin Du's avatar Changbin Du Committed by Jonathan Corbet
Browse files

Documentation: x86: convert microcode.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 ea0765e8

Documentation/x86/index.rst

+1 −0
Original line number Diff line number Diff line
@@ -22,3 +22,4 @@ x86-specific Documentation 
   intel_mpx

   amd-memory-encryption

   pti

   microcode

Documentation/x86/microcode.txt→Documentation/x86/microcode.rst

+34 −28
Original line number Diff line number Diff line 
.. SPDX-License-Identifier: GPL-2.0



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

The Linux Microcode Loader

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



Authors: Fenghua Yu <fenghua.yu@intel.com>

	 Borislav Petkov <bp@suse.de>

:Authors: - Fenghua Yu <fenghua.yu@intel.com>

          - Borislav Petkov <bp@suse.de>



The kernel has a x86 microcode loading facility which is supposed to

provide microcode loading methods in the OS. Potential use cases are
@@ -10,8 +14,8 @@ and updating the microcode on long-running systems without rebooting. 


The loader supports three loading methods:



1. Early load microcode

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

Early load microcode

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



The kernel can update microcode very early during boot. Loading

microcode early can fix CPU issues before they are observed during
@@ -26,8 +30,10 @@ loader parses the combined initrd image during boot. 


The microcode files in cpio name space are:



on Intel: kernel/x86/microcode/GenuineIntel.bin

on AMD  : kernel/x86/microcode/AuthenticAMD.bin

on Intel:

  kernel/x86/microcode/GenuineIntel.bin

on AMD  :

  kernel/x86/microcode/AuthenticAMD.bin



During BSP (BootStrapping Processor) boot (pre-SMP), the kernel

scans the microcode file in the initrd. If microcode matching the
@@ -42,8 +48,8 @@ Here's a crude example how to prepare an initrd with microcode (this is 
normally done automatically by the distribution, when recreating the

initrd, so you don't really have to do it yourself. It is documented

here for future reference only).

::



---

  #!/bin/bash



  if [ -z "$1" ]; then
@@ -76,15 +82,15 @@ here for future reference only). 
  cat ucode.cpio $INITRD.orig > $INITRD



  rm -rf $TMPDIR

---





The system needs to have the microcode packages installed into

/lib/firmware or you need to fixup the paths above if yours are

somewhere else and/or you've downloaded them directly from the processor

vendor's site.



2. Late loading

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

Late loading

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



There are two legacy user space interfaces to load microcode, either through

/dev/cpu/microcode or through /sys/devices/system/cpu/microcode/reload file
@@ -94,7 +100,7 @@ The /dev/cpu/microcode method is deprecated because it needs a special 
userspace tool for that.



The easier method is simply installing the microcode packages your distro

supplies and running:

supplies and running::



  # echo 1 > /sys/devices/system/cpu/microcode/reload
@@ -104,19 +110,19 @@ The loading mechanism looks for microcode blobs in 
/lib/firmware/{intel-ucode,amd-ucode}. The default distro installation

packages already put them there.



3. Builtin microcode

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

Builtin microcode

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



The loader supports also loading of a builtin microcode supplied through

the regular builtin firmware method CONFIG_EXTRA_FIRMWARE. Only 64-bit is

currently supported.



Here's an example:

Here's an example::



  CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin"

  CONFIG_EXTRA_FIRMWARE_DIR="/lib/firmware"



This basically means, you have the following tree structure locally:

This basically means, you have the following tree structure locally::



  /lib/firmware/

  |-- amd-ucode