Based on kernel version 4.0. Page generated on 2015-04-14 21:26 EST.
1 Early load microcode 2 ==================== 3 By Fenghua Yu <email@example.com> 4 5 Kernel can update microcode in early phase of boot time. Loading microcode early 6 can fix CPU issues before they are observed during kernel boot time. 7 8 Microcode is stored in an initrd file. The microcode is read from the initrd 9 file and loaded to CPUs during boot time. 10 11 The format of the combined initrd image is microcode in cpio format followed by 12 the initrd image (maybe compressed). Kernel parses the combined initrd image 13 during boot time. The microcode file in cpio name space is: 14 on Intel: kernel/x86/microcode/GenuineIntel.bin 15 on AMD : kernel/x86/microcode/AuthenticAMD.bin 16 17 During BSP boot (before SMP starts), if the kernel finds the microcode file in 18 the initrd file, it parses the microcode and saves matching microcode in memory. 19 If matching microcode is found, it will be uploaded in BSP and later on in all 20 APs. 21 22 The cached microcode patch is applied when CPUs resume from a sleep state. 23 24 There are two legacy user space interfaces to load microcode, either through 25 /dev/cpu/microcode or through /sys/devices/system/cpu/microcode/reload file 26 in sysfs. 27 28 In addition to these two legacy methods, the early loading method described 29 here is the third method with which microcode can be uploaded to a system's 30 CPUs. 31 32 The following example script shows how to generate a new combined initrd file in 33 /boot/initrd-3.5.0.ucode.img with original microcode microcode.bin and 34 original initrd image /boot/initrd-3.5.0.img. 35 36 mkdir initrd 37 cd initrd 38 mkdir -p kernel/x86/microcode 39 cp ../microcode.bin kernel/x86/microcode/GenuineIntel.bin (or AuthenticAMD.bin) 40 find . | cpio -o -H newc >../ucode.cpio 41 cd .. 42 cat ucode.cpio /boot/initrd-3.5.0.img >/boot/initrd-3.5.0.ucode.img