From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753522AbbDJA4R (ORCPT ); Thu, 9 Apr 2015 20:56:17 -0400 Received: from TYO201.gate.nec.co.jp ([210.143.35.51]:40365 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751731AbbDJA4O convert rfc822-to-8bit (ORCPT ); Thu, 9 Apr 2015 20:56:14 -0400 From: Naoya Horiguchi To: Borislav Petkov CC: "Luck, Tony" , Ingo Molnar , "Prarit Bhargava" , Vivek Goyal , "linux-kernel@vger.kernel.org" , Junichi Nomura , Kiyoshi Ueda Subject: Re: [PATCH v8] x86: mce: kexec: switch MCE handler for kexec/kdump Thread-Topic: [PATCH v8] x86: mce: kexec: switch MCE handler for kexec/kdump Thread-Index: AQHQcQkrDJDcog+fik6X73xFJd9MBZ1Dn7oAgAAd0gCAAAXYgIAACrUAgAAO6wCAAI4vAIAADD6AgABgCIA= Date: Fri, 10 Apr 2015 00:49:33 +0000 Message-ID: <20150410004933.GA21978@hori1.linux.bs1.fc.nec.co.jp> References: <20150406115923.GD4078@pd.tnic> <20150407080017.GB27856@hori1.linux.bs1.fc.nec.co.jp> <20150407080218.GC27856@hori1.linux.bs1.fc.nec.co.jp> <20150409061346.GA25434@pd.tnic> <20150409080030.GA4713@gmail.com> <20150409082125.GE25434@pd.tnic> <20150409085944.GA27042@hori1.linux.bs1.fc.nec.co.jp> <20150409095308.GG25434@pd.tnic> <3908561D78D1C84285E8C5FCA982C28F32A5D502@ORSMSX114.amr.corp.intel.com> <20150409190550.GJ25434@pd.tnic> In-Reply-To: <20150409190550.GJ25434@pd.tnic> Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.26] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 09, 2015 at 09:05:51PM +0200, Borislav Petkov wrote: > On Thu, Apr 09, 2015 at 06:22:02PM +0000, Luck, Tony wrote: > > > Why? Those CPUs are offlined and num_online_cpus() in mce_start() should > > > account for that, no? > > > > > > And if those are offlined, they're very very unlikely to trigger an MCE > > > as they're idle and not executing code. > > > > Let's step back a few feet and look at the big picture. There are three main classes of machine check > > that we might see while trying to run kdump - an remember that all machine checks are currently > > broadcast, so all cpus whether online or offline will see them > > > > 1) Fatal > > We have to crash - lose the dump. Having a new machine check handler will make things a bit easier > > to see what happened because we won't have any synchronization failed messages from the offline > > cpus. > > But this should not be a problem if kdump path keeps cpu_online_mask > uptodate. I'm looking at kdump_nmi_callback() or crash_nmi_callback() or > so. Those should clear cpu_online_mask and then mce_start() will work > fine on the crashing CPU. > > IMHO, of course. Sorry, I misread you. With clearing cpu_online_mask in shootdown (not done yet,) raising tolerance should work without timeout message. So I think you are right. > > 2) Execution path recoverable (SRAR in SDM parlance). > > Also going to be fatal (kdump is all running in ring0, and we can't recover from errors in ring 0). Cleaner > > messages as above. Potentially in the future we might be able to make the kdump machine check handler > > actually recover by just skipping a page - if the location of the error was in the old kernel image. > > > > 3) Non-execution path recoverable (SRAO in SDM) > > We ought to be able to keep kdump running if this happens - the "AO" stands for "action optional", > > so we are going to choose to not take an action. Wherever the error was, it won't affect correctness > > of execution of the current context. > > Those could be simply made to go to dmesg during kdump, i.e. decouple > any MCE consumers. And we do that now anyway, i.e. box without mcelog or > some other ras daemon running. > > So we could reuse the normal handler - we just need to do some tweaking > first... AFAICT, of course. I believe in that endeavor, the devil will > be in the detail. OK, I'll try this approach with updating cpu_online_mask. Thanks, Naoya Horiguchi