1Early load microcode 2==================== 3By Fenghua Yu <fenghua.yu@intel.com> 4 5Kernel can update microcode in early phase of boot time. Loading microcode early 6can fix CPU issues before they are observed during kernel boot time. 7 8Microcode is stored in an initrd file. The microcode is read from the initrd 9file and loaded to CPUs during boot time. 10 11The format of the combined initrd image is microcode in cpio format followed by 12the initrd image (maybe compressed). Kernel parses the combined initrd image 13during boot time. The microcode file in cpio name space is: 14kernel/x86/microcode/GenuineIntel.bin 15 16During BSP boot (before SMP starts), if the kernel finds the microcode file in 17the initrd file, it parses the microcode and saves matching microcode in memory. 18If matching microcode is found, it will be uploaded in BSP and later on in all 19APs. 20 21The cached microcode patch is applied when CPUs resume from a sleep state. 22 23There are two legacy user space interfaces to load microcode, either through 24/dev/cpu/microcode or through /sys/devices/system/cpu/microcode/reload file 25in sysfs. 26 27In addition to these two legacy methods, the early loading method described 28here is the third method with which microcode can be uploaded to a system's 29CPUs. 30 31The following example script shows how to generate a new combined initrd file in 32/boot/initrd-3.5.0.ucode.img with original microcode microcode.bin and 33original initrd image /boot/initrd-3.5.0.img. 34 35mkdir initrd 36cd initrd 37mkdir kernel 38mkdir kernel/x86 39mkdir kernel/x86/microcode 40cp ../microcode.bin kernel/x86/microcode/GenuineIntel.bin 41find .|cpio -oc >../ucode.cpio 42cd .. 43cat ucode.cpio /boot/initrd-3.5.0.img >/boot/initrd-3.5.0.ucode.img 44