Intel Skulake Scalable Platform CPU models that belong to Workstation and HEDT (Basin Falls) segment (SKL-W/X, family 6, model 85, stepping 4) have reports of system hangs on reboot when revision 0x2000065 of microcode, that is included since microcode-20191112 update, is applied[1]. In order to address this, microcode update to this revision has been disabled by default on these systems, and the previously published microcode revision 0x2000064 is used by default for the OS-driven microcode update. [1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/21 For the reference, SHA1 checksums of 06-55-04 microcode files containing microcode revisions in question are listed below: * 06-55-04, revision 0x2000064: 2e405644a145de0f55517b6a9de118eec8ec1e5a * 06-55-04, revision 0x2000065: f27f12b9d53f492c297afd856cdbc596786fad23 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 * CVE-2019-0117 (Intel SGX Information Leak), CVE-2019-0123 (Intel SGX Privilege Escalation), CVE-2019-11135 (TSX Asynchronous Abort), CVE-2019-11139 (Voltage Setting Modulation): https://access.redhat.com/solutions/2019-microcode-nov The information regarding enforcing microcode update is provided below. To enforce usage of the 0x2000065 microcode revision for a specific kernel version, please create a file "force-intel-06-55-04" inside /lib/firmware/ 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 ", 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/force-intel-06-55-04 /usr/libexec/microcode_ctl/update_ucode dracut -f --kver 3.10.0-862.9.1 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. To enforce addition of this microcode for all kernels, please create file "/etc/microcode_ctl/ucode_with_caveats/force-intel-06-55-04", run "/usr/libexec/microcode_ctl/update_ucode" for enabling late microcode updates, and "dracut -f --regenerate-all" for enabling early microcode updates: mkdir -p /etc/microcode_ctl/ucode_with_caveats touch /etc/microcode_ctl/ucode_with_caveats/force-intel-06-55-04 /usr/libexec/microcode_ctl/update_ucode dracut -f --regenerate-all Please refer to /usr/share/doc/microcode_ctl/README.caveats for additional information.