Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 The Linux Microcode Loader 2 3 Authors: Fenghua Yu <fenghua.yu@intel.com> 4 Borislav Petkov <bp@suse.de> 5 6 The kernel has a x86 microcode loading facility which is supposed to 7 provide microcode loading methods in the OS. Potential use cases are 8 updating the microcode on platforms beyond the OEM End-Of-Life support, 9 and updating the microcode on long-running systems without rebooting. 10 11 The loader supports three loading methods: 12 13 1. Early load microcode 14 ======================= 15 16 The kernel can update microcode very early during boot. Loading 17 microcode early can fix CPU issues before they are observed during 18 kernel boot time. 19 20 The microcode is stored in an initrd file. During boot, it is read from 21 it and loaded into the CPU cores. 22 23 The format of the combined initrd image is microcode in (uncompressed) 24 cpio format followed by the (possibly compressed) initrd image. The 25 loader parses the combined initrd image during boot. 26 27 The microcode files in cpio name space are: 28 29 on Intel: kernel/x86/microcode/GenuineIntel.bin 30 on AMD : kernel/x86/microcode/AuthenticAMD.bin 31 32 During BSP (BootStrapping Processor) boot (pre-SMP), the kernel 33 scans the microcode file in the initrd. If microcode matching the 34 CPU is found, it will be applied in the BSP and later on in all APs 35 (Application Processors). 36 37 The loader also saves the matching microcode for the CPU in memory. 38 Thus, the cached microcode patch is applied when CPUs resume from a 39 sleep state. 40 41 Here's a crude example how to prepare an initrd with microcode (this is 42 normally done automatically by the distribution, when recreating the 43 initrd, so you don't really have to do it yourself. It is documented 44 here for future reference only). 45 46 --- 47 #!/bin/bash 48 49 if [ -z "$1" ]; then 50 echo "You need to supply an initrd file" 51 exit 1 52 fi 53 54 INITRD="$1" 55 56 DSTDIR=kernel/x86/microcode 57 TMPDIR=/tmp/initrd 58 59 rm -rf $TMPDIR 60 61 mkdir $TMPDIR 62 cd $TMPDIR 63 mkdir -p $DSTDIR 64 65 if [ -d /lib/firmware/amd-ucode ]; then 66 cat /lib/firmware/amd-ucode/microcode_amd*.bin > $DSTDIR/AuthenticAMD.bin 67 fi 68 69 if [ -d /lib/firmware/intel-ucode ]; then 70 cat /lib/firmware/intel-ucode/* > $DSTDIR/GenuineIntel.bin 71 fi 72 73 find . | cpio -o -H newc >../ucode.cpio 74 cd .. 75 mv $INITRD $INITRD.orig 76 cat ucode.cpio $INITRD.orig > $INITRD 77 78 rm -rf $TMPDIR 79 --- 80 81 The system needs to have the microcode packages installed into 82 /lib/firmware or you need to fixup the paths above if yours are 83 somewhere else and/or you've downloaded them directly from the processor 84 vendor's site. 85 86 2. Late loading 87 =============== 88 89 There are two legacy user space interfaces to load microcode, either through 90 /dev/cpu/microcode or through /sys/devices/system/cpu/microcode/reload file 91 in sysfs. 92 93 The /dev/cpu/microcode method is deprecated because it needs a special 94 userspace tool for that. 95 96 The easier method is simply installing the microcode packages your distro 97 supplies and running: 98 99 # echo 1 > /sys/devices/system/cpu/microcode/reload 100 101 as root. 102 103 The loading mechanism looks for microcode blobs in 104 /lib/firmware/{intel-ucode,amd-ucode}. The default distro installation 105 packages already put them there. 106 107 3. Builtin microcode 108 ==================== 109 110 The loader supports also loading of a builtin microcode supplied through 111 the regular builtin firmware method CONFIG_EXTRA_FIRMWARE. Only 64-bit is 112 currently supported. 113 114 Here's an example: 115 116 CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin" 117 CONFIG_EXTRA_FIRMWARE_DIR="/lib/firmware" 118 119 This basically means, you have the following tree structure locally: 120 121 /lib/firmware/ 122 |-- amd-ucode 123 ... 124 | |-- microcode_amd_fam15h.bin 125 ... 126 |-- intel-ucode 127 ... 128 | |-- 06-3a-09 129 ... 130 131 so that the build system can find those files and integrate them into 132 the final kernel image. The early loader finds them and applies them. 133 134 Needless to say, this method is not the most flexible one because it 135 requires rebuilding the kernel each time updated microcode from the CPU 136 vendor is available.