Microcode
Processor microcode is akin to processor firmware. The kernel is able to update the processor's firmware without the need to update it via a BIOS update.
From the Intel Website:
- "The microcode data file contains the latest microcode definitions for all Intel processors. Intel releases microcode updates to correct processor behavior as documented in the respective processor specification updates. While the regular approach to getting this microcode update is via a BIOS upgrade, Intel realizes that this can be an administrative hassle. The Linux operating system and VMware ESX products have a mechanism to update the microcode after booting. For example, this file will be used by the operating system mechanism if the file is placed in the /etc/firmware directory of the Linux system."
Contents
Updating microcode
For Intel processors, install intel-ucode.
For AMD processors the microcode updates are available in linux-firmware, which is installed as part of the base system.
Enabling Intel microcode updates
These updates must be enabled by adding /boot/intel-ucode.img
as the first initrd in the bootloader config file. This is in addition to the normal initrd file.
Specific examples
EFI boot stub / EFI handover
Append two initrd=
options:
initrd=/intel-ucode.img initrd=/initramfs-linux.img
Gummiboot
Use the initrd
option twice in /boot/loader/entries/*.conf
:
title Arch Linux linux /vmlinuz-linux initrd /intel-ucode.img initrd /initramfs-linux.img options ...
rEFInd
Edit boot options in /boot/refind_linux.conf
as per EFI boot stub above, example:
"Boot with standard options" "ro root=UUID=(...) quiet initrd=intel-ucode.img initrd=initramfs-linux.img"
Users employing manual stanzas in /boot/refind.conf
to define the kernels should simply add initrd=/intel-ucode.img
or /boot/intel-ucode.img
as required to the options line, and not in the main part of the stanza.
Grub
With the release of grub-1:2.02-beta2-5, grub-mkconfig will automatically handle the microcode update. Users are directed to regenerate the grub config to activate loading the microcode update by running # grub-mkconfig -o /boot/grub/grub.cfg
after installing intel-ucode.
Alternatively, users wishing to manage their grub config file manually can add /intel-ucode.img
or /boot/intel-ucode.img
to grub.cfg
as follows:
[...] echo 'Loading initial ramdisk ...' initrd /intel-ucode.img /initramfs-linux.img [...]
Syslinux
Multiple initrd's can be separated by commas in /boot/syslinux/syslinux.cfg
:
LABEL arch MENU LABEL Arch Linux LINUX ../vmlinuz-linux INITRD ../intel-ucode.img,../initramfs-linux.img APPEND ...
Verifying that microcode got updated on boot
Use /usr/bin/dmesg
to see if the microcode has been updated:
$ dmesg | grep microcode
On Intel systems one should see something similar to the following, indicating that microcode is updated early:
[ 0.000000] CPU0 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.221951] CPU1 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.242064] CPU2 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.262349] CPU3 microcode updated early to revision 0x1b, date = 2014-05-29 [ 0.507267] microcode: CPU0 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507272] microcode: CPU1 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507276] microcode: CPU2 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507281] microcode: CPU3 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507286] microcode: CPU4 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507292] microcode: CPU5 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507296] microcode: CPU6 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507300] microcode: CPU7 sig=0x306a9, pf=0x2, revision=0x1b [ 0.507335] microcode: Microcode Update Driver: v2.00 <tigran@aivazian.fsnet.co.uk>, Peter Oruba
It is entirely possible, particularly with newer hardware, that there is no microcode update for the CPU. In that case, the output may look like this:
[ 0.292893] microcode: CPU0 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292899] microcode: CPU1 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292906] microcode: CPU2 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292912] microcode: CPU3 sig=0x306c3, pf=0x2, revision=0x1c [ 0.292956] microcode: Microcode Update Driver: v2.00 <tigran@aivazian.fsnet.co.uk>, Peter Oruba
On AMD systems microcode is updated a bit later in the boot process, so the output would look something like this:
[ 0.807879] microcode: CPU0: patch_level=0x01000098 [ 0.807888] microcode: CPU1: patch_level=0x01000098 [ 0.807983] microcode: Microcode Update Driver: v2.00 <tigran@aivazian.fsnet.co.uk>, Peter Oruba [ 16.150642] microcode: CPU0: new patch_level=0x010000c7 [ 16.150682] microcode: CPU1: new patch_level=0x010000c7
Which CPUs accept microcode updates
Users may consult either Intel or AMD at the following links to see if a particular model is supported:
Detecting available microcode update
It is possible to find out if the intel-ucode.img
contains a microcode image for the running CPU with iucode-tool.
- Install intel-ucode (changing initrd is not required for detection)
- Install iucode-tool from the AUR
-
# modprobe cpuid
-
# bsdtar -Oxf /boot/intel-ucode.img | iucode_tool -tb -lS -
- (extract microcode image and search it for your cpuid)
- If an update is available, it should show up below selected microcodes
Enabling Intel early microcode loading in custom kernels
In order for early loading to work in custom kernels, "CPU microcode loading support" needs to be compiled into the kernel, NOT compiled as a module. This will enable the "Early load microcode" prompt which should be set to "Y".
CONFIG_MICROCODE=y CONFIG_MICROCODE_INTEL=y CONFIG_MICROCODE_INTEL_EARLY=y CONFIG_MICROCODE_EARLY=y