linux-kernel - [PATCH v3 01/10] Documentation/x86: Early load microcode

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Date:	Sun, 16 Dec 2012 02:43:20 -0800
From:	"Fenghua Yu" <fenghua.yu@...el.com>
To:	"H Peter Anvin" <hpa@...or.com>, "Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Asit K Mallick" <asit.k.mallick@...el.com>,
	"Tigran Aivazian" <tigran@...azian.fsnet.co.uk>,
	"Andreas Herrmann" <andreas.herrmann3@....com>,
	"Borislav Petkov" <borislav.petkov@....com>,
	"Yinghai Lu" <yinghai@...nel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"x86" <x86@...nel.org>
Cc:	"Fenghua Yu" <fenghua.yu@...el.com>
Subject: [PATCH v3 01/10] Documentation/x86: Early load microcode

From: Fenghua Yu <fenghua.yu@...el.com>

Documenation for early loading microcode methodology.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 Documentation/x86/early-microcode.txt | 43 +++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 Documentation/x86/early-microcode.txt

diff --git a/Documentation/x86/early-microcode.txt b/Documentation/x86/early-microcode.txt
new file mode 100644
index 0000000..4aaf0df
--- /dev/null
+++ b/Documentation/x86/early-microcode.txt
@@ -0,0 +1,43 @@
+Early load microcode
+====================
+By Fenghua Yu <fenghua.yu@...el.com>
+
+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 an initrd file. The microcode is read from the initrd
+file and loaded to CPUs during boot time.
+
+The format of the combined initrd image is microcode in cpio format followed by
+the 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.bin
+
+During BSP boot (before SMP starts), if the 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
+APs.
+
+The cached microcode patch is applied when CPUs resume from a sleep state.
+
+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.
+
+In addition to these two legacy methods, the early loading method described
+here is the third method with which microcode can be uploaded to a system's
+CPUs.
+
+The following example script shows how to generate a new combined initrd file in
+/boot/initrd-3.5.0.ucode.img with original microcode microcode.bin and
+original initrd image /boot/initrd-3.5.0.img.
+
+mkdir initrd
+cd initrd
+mkdir kernel
+mkdir kernel/x86
+mkdir kernel/x86/microcode
+cp ../microcode.bin kernel/x86/microcode/GenuineIntel.bin
+find .|cpio -oc >../ucode.cpio
+cd ..
+cat ucode.cpio /boot/initrd-3.5.0.img >/boot/initrd-3.5.0.ucode.img
-- 
1.8.0.1

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