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diff --git a/Documentation/x86/microcode.rst b/Documentation/x86/microcode.rst deleted file mode 100644 index a320d37982ed..000000000000 --- a/Documentation/x86/microcode.rst +++ /dev/null @@ -1,142 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -========================== -The Linux Microcode Loader -========================== - -:Authors: - Fenghua Yu <fenghua.yu@intel.com> - - Borislav Petkov <bp@suse.de> - -The kernel has a x86 microcode loading facility which is supposed to -provide microcode loading methods in the OS. Potential use cases are -updating the microcode on platforms beyond the OEM End-Of-Life support, -and updating the microcode on long-running systems without rebooting. - -The loader supports three loading methods: - -Early load microcode -==================== - -The kernel can update microcode very early during boot. Loading -microcode early can fix CPU issues before they are observed during -kernel boot time. - -The microcode is stored in an initrd file. During boot, it is read from -it and loaded into the CPU cores. - -The format of the combined initrd image is microcode in (uncompressed) -cpio format followed by the (possibly compressed) initrd image. The -loader parses the combined initrd image during boot. - -The microcode files in cpio name space are: - -on Intel: - kernel/x86/microcode/GenuineIntel.bin -on AMD : - kernel/x86/microcode/AuthenticAMD.bin - -During BSP (BootStrapping Processor) boot (pre-SMP), the kernel -scans the microcode file in the initrd. If microcode matching the -CPU is found, it will be applied in the BSP and later on in all APs -(Application Processors). - -The loader also saves the matching microcode for the CPU in memory. -Thus, the cached microcode patch is applied when CPUs resume from a -sleep state. - -Here's a crude example how to prepare an initrd with microcode (this is -normally done automatically by the distribution, when recreating the -initrd, so you don't really have to do it yourself. It is documented -here for future reference only). -:: - - #!/bin/bash - - if [ -z "$1" ]; then - echo "You need to supply an initrd file" - exit 1 - fi - - INITRD="$1" - - DSTDIR=kernel/x86/microcode - TMPDIR=/tmp/initrd - - rm -rf $TMPDIR - - mkdir $TMPDIR - cd $TMPDIR - mkdir -p $DSTDIR - - if [ -d /lib/firmware/amd-ucode ]; then - cat /lib/firmware/amd-ucode/microcode_amd*.bin > $DSTDIR/AuthenticAMD.bin - fi - - if [ -d /lib/firmware/intel-ucode ]; then - cat /lib/firmware/intel-ucode/* > $DSTDIR/GenuineIntel.bin - fi - - find . | cpio -o -H newc >../ucode.cpio - cd .. - mv $INITRD $INITRD.orig - cat ucode.cpio $INITRD.orig > $INITRD - - rm -rf $TMPDIR - - -The system needs to have the microcode packages installed into -/lib/firmware or you need to fixup the paths above if yours are -somewhere else and/or you've downloaded them directly from the processor -vendor's site. - -Late loading -============ - -There are two legacy user space interfaces to load microcode, either through -/dev/cpu/microcode or through /sys/devices/system/cpu/microcode/reload file -in sysfs. - -The /dev/cpu/microcode method is deprecated because it needs a special -userspace tool for that. - -The easier method is simply installing the microcode packages your distro -supplies and running:: - - # echo 1 > /sys/devices/system/cpu/microcode/reload - -as root. - -The loading mechanism looks for microcode blobs in -/lib/firmware/{intel-ucode,amd-ucode}. The default distro installation -packages already put them there. - -Builtin microcode -================= - -The loader supports also loading of a builtin microcode supplied through -the regular builtin firmware method CONFIG_EXTRA_FIRMWARE. Only 64-bit is -currently supported. - -Here's an example:: - - CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin" - CONFIG_EXTRA_FIRMWARE_DIR="/lib/firmware" - -This basically means, you have the following tree structure locally:: - - /lib/firmware/ - |-- amd-ucode - ... - | |-- microcode_amd_fam15h.bin - ... - |-- intel-ucode - ... - | |-- 06-3a-09 - ... - -so that the build system can find those files and integrate them into -the final kernel image. The early loader finds them and applies them. - -Needless to say, this method is not the most flexible one because it -requires rebuilding the kernel each time updated microcode from the CPU -vendor is available. |