Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 136 insertions, 0 deletions

diff --git a/Documentation/x86/microcode.txt b/Documentation/x86/microcode.txt
new file mode 100644
index 000000000..79fdb4a81
--- /dev/null
+++ b/Documentation/x86/microcode.txt
@@ -0,0 +1,136 @@
+	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:
+
+1. 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.
+
+2. 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.
+
+3. 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.