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Intel Broadwell-EP/EX (BDX-ML B/M/R0, family 6, model 79, stepping 1) has issues
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with microcode update that may lead to a system hang; while some changes
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to the Linux kernel have been made in an attempt to address these issues,
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they were not eliminated, so a possibility of unstable system behaviour
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after a microcode update performed on a running system is still present even
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on a kernels that contain aforementioned changes. As a result, microcode update
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for this CPU model has been disabled by default.
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For the reference, kernel versions for the respective RHEL minor versions
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that contain the aforementioned changes, are listed below:
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* Upstream/RHEL 8: kernel-4.17.0 or newer;
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* RHEL 7.6 onwards: kernel-3.10.0-894 or newer;
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* RHEL 7.5.z: kernel-3.10.0-862.6.1 or newer;
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* RHEL 7.4.z: kernel-3.10.0-693.35.1 or newer;
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* RHEL 7.3.z: kernel-3.10.0-514.52.1 or newer;
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* RHEL 7.2.z: kernel-3.10.0-327.70.1 or newer.
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Please contact you system vendor for a BIOS/firmware update that contains
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the latest microcode version. For the information regarding microcode versions
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required for mitigating specific side-channel cache attacks, please refer
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to the following knowledge base articles:
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* CVE-2017-5715 ("Spectre"):
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https://access.redhat.com/articles/3436091
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* CVE-2018-3639 ("Speculative Store Bypass"):
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https://access.redhat.com/articles/3540901
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* CVE-2018-3620, CVE-2018-3646 ("L1 Terminal Fault Attack"):
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https://access.redhat.com/articles/3562741
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* CVE-2018-12130, CVE-2018-12126, CVE-2018-12127, and CVE-2019-11091
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("Microarchitectural Data Sampling"):
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https://access.redhat.com/articles/4138151
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The information regarding enforcing microcode load is provided below.
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For enforcing addition of this microcode to the firmware directory
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for a specific kernel, where it is available for a late microcode update,
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please create a file "force-late-intel-06-4f-01" inside
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/lib/firmware/<kernel_version> directory and run
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"/usr/libexec/microcode_ctl/update_ucode":
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touch /lib/firmware/3.10.0-862.9.1/force-late-intel-06-4f-01
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/usr/libexec/microcode_ctl/update_ucode
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After that, it is possible to perform a late microcode update by executing
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"/usr/libexec/microcode_ctl/reload_microcode" or by writing value "1" to
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"/sys/devices/system/cpu/microcode/reload" directly.
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For enforcing addition of this microcode to firmware directories for all
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kernels, please create a file
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"/etc/microcode_ctl/ucode_with_caveats/force-late-intel-06-4f-01"
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and run "/usr/libexec/microcode_ctl/update_ucode":
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touch /etc/microcode_ctl/ucode_with_caveats/force-late-intel-06-4f-01
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/usr/libexec/microcode_ctl/update_ucode
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For enforcing early load of this microcode for a specific kernel, please
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create a file "force-early-intel-06-4f-01" inside
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"/lib/firmware/<kernel_version>" directory and run
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"dracut -f --kver <kernel_version>":
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touch /lib/firmware/3.10.0-862.9.1/force-early-intel-06-4f-01
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dracut -f --kver 3.10.0-862.9.1
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For enforcing early load of this microcode for all kernels, please
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create a file "/etc/microcode_ctl/ucode_with_caveats/force-early-intel-06-4f-01"
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and run dracut -f --regenerate-all:
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touch /etc/microcode_ctl/ucode_with_caveats/force-early-intel-06-4f-01
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dracut -f --regenerate-all
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If you want avoid removal of the microcode file during cleanup performed by
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/usr/libexec/microcode_ctl/update_ucode, please remove the corresponding readme
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file (/lib/firmware/<kernel_version>/readme-intel-06-4f-01).
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Please refer to /usr/share/doc/microcode_ctl/README.caveats for additional
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information.
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