Intel Broadwell-EP/EX (BDX-ML B/M/R0, family 6, model 79, stepping 1) has issues

with microcode update that may lead to a system hang; while some changes

to the Linux kernel have been made in an attempt to address these issues,

they were not eliminated, so a possibility of unstable system behaviour

after a microcode update performed on a running system is still present even

on a kernels that contain aforementioned changes.  As a result, microcode update

for this CPU model has been disabled by default.

For the reference, kernel versions for the respective RHEL minor versions

that contain the aforementioned changes, are listed below:

 * Upstream/RHEL 8: kernel-4.17.0 or newer;

 * RHEL 7.6 onwards: kernel-3.10.0-894 or newer;

 * RHEL 7.5.z: kernel-3.10.0-862.6.1 or newer;

 * RHEL 7.4.z: kernel-3.10.0-693.35.1 or newer;

 * RHEL 7.3.z: kernel-3.10.0-514.52.1 or newer;

 * RHEL 7.2.z: kernel-3.10.0-327.70.1 or newer.

Please contact you system vendor for a BIOS/firmware update that contains

the latest microcode version. For the information regarding microcode versions

required for mitigating specific side-channel cache attacks, please refer

to the following knowledge base articles:

 * CVE-2017-5715 ("Spectre"):

   https://access.redhat.com/articles/3436091

 * CVE-2018-3639 ("Speculative Store Bypass"):

   https://access.redhat.com/articles/3540901

 * CVE-2018-3620, CVE-2018-3646 ("L1 Terminal Fault Attack"):

   https://access.redhat.com/articles/3562741

 * CVE-2018-12130, CVE-2018-12126, CVE-2018-12127, and CVE-2019-11091

   ("Microarchitectural Data Sampling"):

   https://access.redhat.com/articles/4138151

The information regarding enforcing microcode load is provided below.

For enforcing addition of this microcode to the firmware directory

for a specific kernel, where it is available for a late microcode update,

please create a file "force-late-intel-06-4f-01" inside

/lib/firmware/<kernel_version> directory and run

"/usr/libexec/microcode_ctl/update_ucode":

    touch /lib/firmware/3.10.0-862.9.1/force-late-intel-06-4f-01

    /usr/libexec/microcode_ctl/update_ucode

After that, it is possible to perform a late microcode update by executing

"/usr/libexec/microcode_ctl/reload_microcode" or by writing value "1" to

"/sys/devices/system/cpu/microcode/reload" directly.

For enforcing addition of this microcode to firmware directories for all

kernels, please create a file

"/etc/microcode_ctl/ucode_with_caveats/force-late-intel-06-4f-01"

and run "/usr/libexec/microcode_ctl/update_ucode":

    mkdir -p /etc/microcode_ctl/ucode_with_caveats

    touch /etc/microcode_ctl/ucode_with_caveats/force-late-intel-06-4f-01

    /usr/libexec/microcode_ctl/update_ucode

For enforcing early load of this microcode for a specific kernel, please

create a file "force-early-intel-06-4f-01" inside

"/lib/firmware/<kernel_version>" directory and run

"dracut -f --kver <kernel_version>":

    touch /lib/firmware/3.10.0-862.9.1/force-early-intel-06-4f-01

    dracut -f --kver 3.10.0-862.9.1

For enforcing early load of this microcode for all kernels, please

create a file "/etc/microcode_ctl/ucode_with_caveats/force-early-intel-06-4f-01"

and run dracut -f --regenerate-all:

    mkdir -p /etc/microcode_ctl/ucode_with_caveats

    touch /etc/microcode_ctl/ucode_with_caveats/force-early-intel-06-4f-01

    dracut -f --regenerate-all

If you want to avoid removal of the microcode file during cleanup performed by

/usr/libexec/microcode_ctl/update_ucode, please remove the corresponding readme

file (/lib/firmware/<kernel_version>/readme-intel-06-4f-01).

Please refer to /usr/share/doc/microcode_ctl/README.caveats for additional

information.