From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96BFFC4BA25 for ; Wed, 26 Feb 2020 18:42:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B6C320714 for ; Wed, 26 Feb 2020 18:42:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="PUNAfuZ9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727154AbgBZSmn (ORCPT ); Wed, 26 Feb 2020 13:42:43 -0500 Received: from mail.skyhub.de ([5.9.137.197]:60252 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726878AbgBZSmn (ORCPT ); Wed, 26 Feb 2020 13:42:43 -0500 Received: from zn.tnic (p200300EC2F08E3000C0800EF15AE70EC.dip0.t-ipconnect.de [IPv6:2003:ec:2f08:e300:c08:ef:15ae:70ec]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id B5F311EC01D4; Wed, 26 Feb 2020 19:42:41 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1582742561; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=QOLbKvGIVeO+bnGDtjPE871jDv/Zu6peumehaSdxHyI=; b=PUNAfuZ9Ok7gAisFgmN/CJ9//QKmrwEcmX8++apJPH9cVaoioOMquyHvIaq976PMUXAiCL LCZrN30lSazsb23bnTSY4o3xDbSPAdeYFLsUvIilpNbZPIyZG0kJ9D6RdKPlgiT3V1bfqH 05lpe1sc/+ybTGPsU6t4SVGmlENaOFQ= Date: Wed, 26 Feb 2020 19:42:37 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: Peter Zijlstra , Andy Lutomirski , Frederic Weisbecker , Thomas Gleixner , LKML , X86 ML , Steven Rostedt , Brian Gerst , Juergen Gross , Paolo Bonzini , Arnd Bergmann Subject: Re: [patch 02/10] x86/mce: Disable tracing and kprobes on do_machine_check() Message-ID: <20200226184237.GB16756@zn.tnic> References: <20200226160818.GY18400@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 26, 2020 at 09:28:51AM -0800, Andy Lutomirski wrote: > > It entirely depends on what the goal is :-/ On the one hand I see why > > people might want function tracing / kprobes enabled, OTOH it's all > > mighty frigging scary. Any tracing/probing/whatever on an MCE has the > > potential to make a bad situation worse -- not unlike the same on #DF. FWIW, I had this at the beginning of the #MC handler in a feeble attempt to poke at this: + hw_breakpoint_disable(); + static_key_disable(&__tracepoint_read_msr.key); + tracing_off(); But then Tony noted that some recoverable errors do get reported with an #MC exception so we would have to look at the error severity and then decide whether to allow tracing or not. But the error severity happens all the way down in __mc_scan_banks() - i.e., we've executed the half handler already. So, frankly, I wanna say, f*ck tracing etc - there are certain handlers which simply don't allow it. And we'll only consider changing that when a really good reason for it appears... -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette