From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756865Ab3AaWZT (ORCPT ); Thu, 31 Jan 2013 17:25:19 -0500 Received: from terminus.zytor.com ([198.137.202.10]:44833 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756570Ab3AaWZR (ORCPT ); Thu, 31 Jan 2013 17:25:17 -0500 Date: Thu, 31 Jan 2013 14:25:04 -0800 From: tip-bot for Fenghua Yu Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, fenghua.yu@intel.com, tglx@linutronix.de, hpa@linux.intel.com Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, fenghua.yu@intel.com, tglx@linutronix.de, hpa@linux.intel.com In-Reply-To: <1356075872-3054-2-git-send-email-fenghua.yu@intel.com> References: <1356075872-3054-2-git-send-email-fenghua.yu@intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/microcode] x86, doc: Documentation for early microcode loading Git-Commit-ID: 0d91ea86a895b911fd7d999acb3f600706d9c8cd X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (terminus.zytor.com [127.0.0.1]); Thu, 31 Jan 2013 14:25:09 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 0d91ea86a895b911fd7d999acb3f600706d9c8cd Gitweb: http://git.kernel.org/tip/0d91ea86a895b911fd7d999acb3f600706d9c8cd Author: Fenghua Yu AuthorDate: Thu, 20 Dec 2012 23:44:21 -0800 Committer: H. Peter Anvin CommitDate: Thu, 31 Jan 2013 13:18:47 -0800 x86, doc: Documentation for early microcode loading Documenation for early loading microcode methodology. Signed-off-by: Fenghua Yu Link: http://lkml.kernel.org/r/1356075872-3054-2-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin --- Documentation/x86/early-microcode.txt | 43 +++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) 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