[PATCH 01/11] Documentation/x86: Early load microcode

["Fenghua Yu" <fenghua.yu@xxxxxxxxx>]

From: Fenghua Yu <fenghua.yu@xxxxxxxxx>

Documenation for early load microcode methodology.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
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 Documentation/x86/earlyucode.txt |   43 ++++++++++++++++++++++++++++++++++++++
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+Early load microcode
+====================
+By Fenghua Yu <fenghua.yu@xxxxxxxxx>
+
+Kernel can update microcode in early phase of boot time. Loading microcode early
+can fix CPU issues before they are observed during kernel boot time.
+
+Microcode is stored in initrd file. The microcode is read from the initrd file
+and loaded to CPU's during boot time.
+
+The format of the combined initrd image is microcode in cpio format followed by
+initrd image (maybe compressed). Kernel parses the combined initrd image during
+boot time. The microcode file in cpio name space is:
+kernel/x86/microcode/GenuineIntel/microcode.hex
+
+During BSP boot (before SMP starts), if kernel finds the microcode file in the
+initrd file, it parses the microcode and saves matching microcode in memory.
+If matching microcode is found, it will be uploaded in BSP and later on in all
+AP's.
+
+The saved microcode in memory will be used to upload micorcode when system
+resumes from sleep.
+
+In the past, user can issue command to load microcode during run time. There are
+two user space interfaces to load microcode, either through /dev/cpu/microcode
+interface or through reload file in sysfs.
+
+Now user can choose any of the three methods to update microcode during boot
+time or later during run time.
+
+The following sample script shows how to generate a new combined initrd file in
+/boot/initrd-3.5.0.ucode.img with original microcode microcode.hex and
+original initrd image /boot/initrd-3.5.0.img.
+
+mkdir initrd
+cd initrd
+cp ../microcode.hex kernel/x86/microcode/GenuineIntel/microcode.hex
+find .|cpio -oc >../ucode.cpio
+cd ..
+cat ucode.cpio /boot/initrd-3.5.0.img >/boot/initrd-3.5.0.ucode.img
+
+The generated /boot/initrd-3.5.0.ucode.img can be used as initrd file to load
+microcode during early boot time.
-- 
1.7.2

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