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Fenghua Yu0d91ea82012-12-20 23:44:21 -08001Early 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:
Jacob Shin757885e2013-05-30 14:09:19 -050014on Intel: kernel/x86/microcode/GenuineIntel.bin
15on AMD : kernel/x86/microcode/AuthenticAMD.bin
Fenghua Yu0d91ea82012-12-20 23:44:21 -080016
17During BSP boot (before SMP starts), if the kernel finds the microcode file in
18the initrd file, it parses the microcode and saves matching microcode in memory.
19If matching microcode is found, it will be uploaded in BSP and later on in all
20APs.
21
22The cached microcode patch is applied when CPUs resume from a sleep state.
23
24There are two legacy user space interfaces to load microcode, either through
25/dev/cpu/microcode or through /sys/devices/system/cpu/microcode/reload file
26in sysfs.
27
28In addition to these two legacy methods, the early loading method described
29here is the third method with which microcode can be uploaded to a system's
30CPUs.
31
32The 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
34original initrd image /boot/initrd-3.5.0.img.
35
36mkdir initrd
37cd initrd
Jacob Shin757885e2013-05-30 14:09:19 -050038mkdir -p kernel/x86/microcode
39cp ../microcode.bin kernel/x86/microcode/GenuineIntel.bin (or AuthenticAMD.bin)
40find . | cpio -o -H newc >../ucode.cpio
Fenghua Yu0d91ea82012-12-20 23:44:21 -080041cd ..
42cat ucode.cpio /boot/initrd-3.5.0.img >/boot/initrd-3.5.0.ucode.img
Borislav Petkovb5843032016-02-03 12:33:45 +010043
44Builtin microcode
45=================
46
47We can also load builtin microcode supplied through the regular firmware
Borislav Petkov9f3cc2a2016-06-06 17:10:50 +020048builtin method CONFIG_FIRMWARE_IN_KERNEL. Only 64-bit is currently
49supported.
50
51Here's an example:
Borislav Petkovb5843032016-02-03 12:33:45 +010052
53CONFIG_FIRMWARE_IN_KERNEL=y
54CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin"
55CONFIG_EXTRA_FIRMWARE_DIR="/lib/firmware"
56
57This basically means, you have the following tree structure locally:
58
59/lib/firmware/
60|-- amd-ucode
61...
62| |-- microcode_amd_fam15h.bin
63...
64|-- intel-ucode
65...
66| |-- 06-3a-09
67...
68
69so that the build system can find those files and integrate them into
70the final kernel image. The early loader finds them and applies them.