gentoo intel-ucode microcode

gentoo provides a package for intel microcode updates to safely update cpu firmwares. this is how i adapted the gentoo way.

$ vi /etc/portage/make.conf
MICROCODE_SIGNATURES="-S"

without the above line, all microcodes for every cpu are generated: 95 files in my case.
with the above line, only the microcodes with cpu signatures specific to my processor are generated: 6 files only in my case now.

$ vi /etc/portage/package.use
sys-firmware/intel-microcode initramfs

# emerge sys-firmware/intel-microcode

These are the packages that would be merged:

Calculating dependencies... done!
[ebuild   R    ] sys-firmware/intel-microcode-20180108-r1::gentoo  USE="initramfs* split-ucode" 0 KiB

Total: 1 package (1 reinstall), Size of downloads: 0 KiB

Would you like to merge these packages? [Yes/No] y
>>> Verifying ebuild manifests
>>> Running pre-merge checks for sys-firmware/intel-microcode-20180108-r1
 * MICROCODE_SIGNATURES is set!
 * The user has decided to install only a SUBSET of microcode.
 * To avoid automounting and auto(un)installing with /boot,
 * just export the DONT_MOUNT_BOOT variable.

 * Assuming you do not have a separate /boot partition.
>>> Emerging (1 of 1) sys-firmware/intel-microcode-20180108-r1::gentoo
>>> Installing (1 of 1) sys-firmware/intel-microcode-20180108-r1::gentoo
>>> Jobs: 1 of 1 complete                           Load avg: 1.78, 1.46, 1.57

 * Messages for package sys-firmware/intel-microcode-20180108-r1:

 * MICROCODE_SIGNATURES is set!
 * The user has decided to install only a SUBSET of microcode.
 * To avoid automounting and auto(un)installing with /boot,
 * just export the DONT_MOUNT_BOOT variable.
>>> Auto-cleaning packages...

>>> No outdated packages were found on your system.

 * GNU info directory index is up-to-date.

now to edit my custom grub.cfg

# vi /boot/grub/grub.cfg
initrd /boot/intel-uc.img /boot/initramfs

reboot and check dmesg to confirm microcode updates.

$ dmesg | grep microcode