From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752296Ab2LUCu6 (ORCPT ); Thu, 20 Dec 2012 21:50:58 -0500 Received: from mga01.intel.com ([192.55.52.88]:39623 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751745Ab2LUCum (ORCPT ); Thu, 20 Dec 2012 21:50:42 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,327,1355126400"; d="scan'208";a="265338727" From: "Fenghua Yu" To: "H Peter Anvin" , "Ingo Molnar" , "Thomas Gleixner" , "Asit K Mallick" , "Tigran Aivazian" , "Yinghai Lu" , "Andreas Herrmann" , "Borislav Petkov" , "linux-kernel" , "x86" Cc: "Fenghua Yu" Subject: [PATCH v4 01/11] Documentation/x86: Early load microcode Date: Thu, 20 Dec 2012 11:48:03 -0800 Message-Id: <1356032893-2730-2-git-send-email-fenghua.yu@intel.com> X-Mailer: git-send-email 1.7.2 In-Reply-To: <1356032893-2730-1-git-send-email-fenghua.yu@intel.com> References: <1356032893-2730-1-git-send-email-fenghua.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Fenghua Yu Documenation for early loading microcode methodology. Signed-off-by: Fenghua Yu --- 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 + +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