# Microcode

Processor manufacturers release stability and security updates to the processor microcode. While microcode can be updated through the BIOS, the Linux kernel is also able to apply these updates during boot. These updates provide bug fixes that can be critical to the stability of your system. Without these updates, you may experience spurious crashes or unexpected system halts that can be difficult to track down.

Users of CPUs belonging to the Intel Haswell and Broadwell processor families in particular must install these microcode updates to ensure system stability. But all Intel users should install the updates as a matter of course.

## Installation

For AMD processors the microcode updates are available in linux-firmware, which is installed as part of the base system. No further action is needed.

For Intel processors, install the intel-ucode package, and continue reading.

## Enabling Intel microcode updates

Microcode must be loaded by the bootloader. Because of the wide variability in users' early-boot configuration, Intel microcode updates may not be triggered automatically by Arch's default configuration. Many AUR kernels have followed the path of the official Arch kernels in this regard.

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. See below for instructions for common bootloaders.

### GRUB

#### Automatic method

grub-mkconfig will automatically detect the microcode update and configure GRUB appropriately. After installing the intel-ucode package, users are directed to regenerate the GRUB config to activate loading the microcode update by running:

    # grub-mkconfig -o /boot/grub/grub.cfg

#### Manual method

Alternatively, users that 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
    [...]

Repeat it for each menu entry.

Warning: This file will automatically be overwritten by `/usr/bin/grub-mkconfig` during certain updates negating the changes. It is strongly recommended to use the configuration directory in `/etc/grub.d/` to manage your GRUB configuration needs.

### systemd-boot

Use the `initrd` option twice in `/boot/loader/entries/entry.conf`:

    title   Arch Linux
    linux   /vmlinuz-linux
    initrd  /intel-ucode.img
    initrd  /initramfs-linux.img
    options ...

If you do not mount the ESP to `/boot`, copy `/boot/intel-ucode.img` to your EFI System Partition.

### EFI boot stub / EFI handover

Append two `initrd=` options:

    initrd=/intel-ucode.img initrd=/initramfs-linux.img

The factual accuracy of this article or section is disputed.

Reason: What does this do, why isn't the above enough and why/how is it specific to this particular section? (Discuss in Talk:Microcode#)

For kernels that have been generated as a single file containing all initrd, cmdline and kernel, first generate the initrd to integrate by creating a new one as follows:

    cat /boot/intel-ucode.img /boot/initramfs-linux.img > my_new_initrd
    objcopy ... --add-section .initrd=my_new_initrd

### rEFInd

Edit boot options in `/boot/refind_linux.conf` as per EFI boot stub above, example:

    "Boot with standard options" "rw root=UUID=(...) quiet initrd=/boot/intel-ucode.img initrd=/boot/initramfs-linux.img"

Users employing manual stanzas in `esp/EFI/refind/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.

### Syslinux

Note: There must be no spaces between the `intel-ucode` and `initramfs-linux` initrd files. The period signs also do not signify any shorthand or missing code; the `INITRD` line must be exactly as illustrated below.

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 <your kernel parameters>

### LILO

LILO and potentially other old bootloaders do not support multiple initrd images. In that case, `intel-ucode` and `initramfs-linux` will have to be merged into one image.

Warning: The merged image must be recreated after each kernel update!
Note: The additional image, in this case `intel-ucode` must not be compressed. Otherwise, the kernel might complain that it can only find garbage in the uncompressed image and fail to boot.

`intel-ucode.img` should be a cpio archive, as in this case. It is advised to check whether the archive is compressed after each microcode update, as there is no guarantee that the image will stay non-compressed in the future. In order to check whether `intel-ucode` is compressed, you can use the `file` command:

    $ file /boot/intel-ucode.img
    /boot/intel-ucode.img: ASCII cpio archive (SVR4 with no CRC)

Note: The order is important. The original image `initramfs-linux` must be concatenated on top of the `intel-ucode` image.

To merge both images into one image named `initramfs-merged.img`, the following command can be used:

    # cat /boot/intel-ucode.img /boot/initramfs-linux.img > /boot/initramfs-merged.img

Now, edit `/etc/lilo.conf` to load the new image.

    [...]
       initrd=/boot/initramfs-merged.img
    [...]

And run `lilo` as root:

    # lilo

## 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

Note: The date displayed does not correspond to the version of the intel-ucode package installed. It does show the last time Intel updated the microcode that corresponds to the specific hardware being updated.

## Which CPUs accept microcode updates

Users may consult either Intel or AMD at the following links to see if a particular model is supported:

- AMD's Operating System Research Center.
- Intel's download center.

### 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-toolAUR.

- Install intel-ucode (changing initrd is not required for detection)
- Install iucode-toolAUR 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
- The microcode might already be in your vendor bios and not show up loading in dmesg. Compare to the current microcode running `grep microcode /proc/cpuinfo`

## 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_BLK_DEV_INITRD=Y
    CONFIG_MICROCODE=y
    CONFIG_MICROCODE_INTEL=Y

## See also

- Updating microcodes
- Notes on Intel Microcode updates
- Kernel early microcode
- Erratum found in Haswell/Broadwell
- Technical details

Category:

- CPU

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