Intel Sandy Bridge-E/EN/EP CPU models (SNB-EP, family 6, model 45, stepping 7)

had issues with MDS-related microcode update that may lead to a system hang

after a microcode update[1][2].  In order to address this, microcode update

to the MDS-related revision 0x718 had been disabled, and the previously

published microcode revision 0x714 is used by default for the OS-driven

microcode update.  The revision 0x71a of the microcode is intended to fix

the aforementioned issue, hence it is enabled by default (but can be disabled

explicitly; see below).

[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/15

[2] https://access.redhat.com/solutions/4593951

For the reference, SHA1 checksums of 06-2d-07 microcode files containing

microcode revisions in question are listed below:

 * 06-2d-07, revision 0x714: bcf2173cd3dd499c37defbc2533703cfa6ec2430

 * 06-2d-07, revision 0x718: 837cfebbfc09b911151dfd179082ad99cf87e85d

 * 06-2d-07, revision 0x71a: 4512c8149e63e5ed15f45005d7fb5be0041f66f6

Please contact your 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 disabling microcode update is provided below.

To disable usage of the newer microcode revision for a specific kernel

version, please create file "disallow-intel-06-2d-07" inside

/lib/firmware/<kernel_version> directory, run

"/usr/libexec/microcode_ctl/update_ucode" to add it to firmware directory

where microcode will be available for late microcode update, and run

"dracut -f --kver <kernel_version>", so initramfs for this kernel version

is regenerated and the microcode can be loaded early, for example:

    touch /lib/firmware/3.10.0-862.9.1/disallow-intel-06-2d-07

    /usr/libexec/microcode_ctl/update_ucode

    dracut -f --kver 3.10.0-862.9.1

To avoid addition of the newer microcode revision for all kernels, please create

file "/etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-2d-07", run

"/usr/libexec/microcode_ctl/update_ucode" for late microcode updates,

and "dracut -f --regenerate-all" for early microcode updates:

    mkdir -p /etc/microcode_ctl/ucode_with_caveats

    touch /etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-2d-07

    /usr/libexec/microcode_ctl/update_ucode

    dracut -f --regenerate-all

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

information.