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Documentation / x86 / early-microcode.txt

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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:56 EST.

1	Early load microcode
2	====================
3	By Fenghua Yu <fenghua.yu@intel.com>
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.
8	Microcode is stored in an initrd file. The microcode is read from the initrd
9	file and loaded to CPUs during boot time.
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
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.
22	The cached microcode patch is applied when CPUs resume from a sleep state.
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.
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.
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.
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
44	Builtin microcode
45	=================
47	We can also load builtin microcode supplied through the regular firmware
48	builtin method CONFIG_FIRMWARE_IN_KERNEL. Only 64-bit is currently
49	supported.
51	Here's an example:
54	CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin"
55	CONFIG_EXTRA_FIRMWARE_DIR="/lib/firmware"
57	This basically means, you have the following tree structure locally:
59	/lib/firmware/
60	|-- amd-ucode
61	...
62	|   |-- microcode_amd_fam15h.bin
63	...
64	|-- intel-ucode
65	...
66	|   |-- 06-3a-09
67	...
69	so that the build system can find those files and integrate them into
70	the final kernel image. The early loader finds them and applies them.
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