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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.