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Older RHEL 7 kernels try to early load microcode even inside virtual
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machine, which may lead to panic on some hypervisors. In order to circumvent
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that, microcode is installed into a kernel-version-specific directory (which
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is not scanned by the dracut script, that constructs early microcode binary
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in initramfs, by default), and path to microcode files provided only in case
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initramfs is generated for the kernel version that properly handles early
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microcode inside a virtual machine (i.e. do not attempts yo load it).
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The versions of the kernel package that properly handle early microcode load
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inside a virtual machine are as follows:
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* RHEL 7.6 onwards: kernel-3.10.0-930 or newer;
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* RHEL 7.5: kernel-3.10.0-862.14.1 or newer;
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* RHEL 7.4: kernel-3.10.0-693.38.1 or newer;
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* RHEL 7.3: kernel-3.10.0-514.57.1 or newer;
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* RHEL 7.2: kernel-3.10.0-327.73.1 or newer.
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RHEL 8 kernels are not affected.
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If you want to avoid early load of microcode for a specific kernel, please
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create "disallow-early-intel" file inside /lib/firmware/<kernel_version>
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directory and run dracut -f --kver "<kernel_version>":
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touch /lib/firmware/3.10.0-862.9.1/disallow-intel
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/usr/libexec/microcode_ctl/update_ucode
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dracut -f --kver 3.10.0-862.9.1
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If you want to avoid early load of microcode for all kernels, please create
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"disallow-early-intel" file inside the "/etc/microcode_ctl/ucode_with_caveats"
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directory and run dracut -f --regenerate-all:
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mkdir -p /etc/microcode_ctl/ucode_with_caveats
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touch /etc/microcode_ctl/ucode_with_caveats/disallow-intel
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dracut -f --kver 3.10.0-862.9.1
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If you want to enforce early load of microcode for a specific kernel, please
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create "force-early-intel" file inside /lib/firmware/<kernel_version> directory
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and run dracut -f --kver "<kernel_version>":
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modir -p/lib/firmware/3.10.0-862.9.1/
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touch /lib/firmware/3.10.0-862.9.1/force-early-intel
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dracut -f --kver 3.10.0-862.9.1
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If you want to enforce early load of microcode for all kernels, please create
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"force-early-intel" file inside /etc/microcode_ctl/ucode_with_caveats
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directory and run dracut -f --kver "<kernel_version>":
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mkdir -p /etc/microcode_ctl/ucode_with_caveats
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touch /etc/microcode_ctl/ucode_with_caveats/force-early-intel
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dracut -f --regenerate-all
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In order to override late load behaviour, the "early" part of file names should
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be replaced with "late" (and there is no need to call dracut in that case).
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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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