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editing: readme-intel-06-8f-08

Intel Sapphire Rapids Edge Enhanced CPU models (SPR-EE, family 6, model 143,
stepping 8) had reports of system exhibiting latency spikes when revsions
0x2b000603 and newer of the microcode are applied.  In order to address this,
previous 0x2b0005c0 revision of the microcode is provided, and the usage
of the latest microcode can be disabled (see below), so the older version
is used instead.

For the reference, SHA1 checksums of 06-8f-08 microcode files containing
microcode revisions in question are listed below:
 * 06-8f-08, revision 0x2b0005c0: adf8b6aa2718ff16f3d19d34ec389270073d2b5e
 * 06-8f-08, revision 0x2b000603: 729014bd05dfb6593152ea7ee12330791bc22bec
 * 06-8f-08, revision 0x2b000620: e39812f7aff520c79f3f6fa013bd501781d92f8e
 * 06-8f-08, revision 0x2b000639: 39d91f7a962245ba79fea0611732c86efbd71bc5

Please contact your system vendor for a BIOS/firmware update that contains
the latest microcode version.

The information regarding disabling microcode update is provided below.

To disable usage of the newer microcode revision for a specific kernel
version, please create a file "disallow-intel-06-8f-08" inside
/lib/firmware/<kernel_version> directory, run
"/usr/libexec/microcode_ctl/update_ucode" to update firmware directory
used for late microcode updates, and run "dracut -f --kver <kernel_version>"
so initramfs for this kernel version is regenerated, for example:

touch /lib/firmware/3.10.0-862.9.1/disallow-intel-06-8f-08
    /usr/libexec/microcode_ctl/update_ucode
    dracut -f --kver 3.10.0-862.9.1

To disable usage of the newer microcode revision for all kernels, please create
file "/etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-8f-08", run
"/usr/libexec/microcode_ctl/update_ucode" to update firmware directories
used for late microcode updates, and run "dracut -f --regenerate-all"
so initramfs images get regenerated, for example:

mkdir -p /etc/microcode_ctl/ucode_with_caveats
    touch /etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-8f-0f
    /usr/libexec/microcode_ctl/update_ucode
    dracut -f --regenerate-all

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

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