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=-7.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 120E7C433DF for ; Fri, 7 Aug 2020 12:04:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE1A22075D for ; Fri, 7 Aug 2020 12:04:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728367AbgHGMEZ (ORCPT ); Fri, 7 Aug 2020 08:04:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:50742 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727783AbgHGMEZ (ORCPT ); Fri, 7 Aug 2020 08:04:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 2B4E4AF4E; Fri, 7 Aug 2020 12:04:41 +0000 (UTC) Subject: Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers To: Marco Elver Cc: Peter Zijlstra , Borislav Petkov , Dave Hansen , fenghua.yu@intel.com, "H. Peter Anvin" , LKML , Ingo Molnar , syzkaller-bugs , Thomas Gleixner , "Luck, Tony" , the arch/x86 maintainers , yu-cheng.yu@intel.com, sdeep@vmware.com, virtualization@lists.linux-foundation.org, kasan-dev , syzbot , "Paul E. McKenney" References: <20200806074723.GA2364872@elver.google.com> <20200806113236.GZ2674@hirez.programming.kicks-ass.net> <20200806131702.GA3029162@elver.google.com> <20200807095032.GA3528289@elver.google.com> <16671cf3-3885-eb06-79ff-4cbfaeeaea79@suse.com> <20200807113838.GA3547125@elver.google.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: Date: Fri, 7 Aug 2020 14:04:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200807113838.GA3547125@elver.google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07.08.20 13:38, Marco Elver wrote: > On Fri, Aug 07, 2020 at 12:35PM +0200, Jürgen Groß wrote: >> On 07.08.20 11:50, Marco Elver wrote: >>> On Fri, Aug 07, 2020 at 11:24AM +0200, Jürgen Groß wrote: >>>> On 07.08.20 11:01, Marco Elver wrote: >>>>> On Thu, 6 Aug 2020 at 18:06, Marco Elver wrote: >>>>>> On Thu, 6 Aug 2020 at 15:17, Marco Elver wrote: >>>>>>> On Thu, Aug 06, 2020 at 01:32PM +0200, peterz@infradead.org wrote: >>>>>>>> On Thu, Aug 06, 2020 at 09:47:23AM +0200, Marco Elver wrote: >>>>>>>>> Testing my hypothesis that raw then nested non-raw >>>>>>>>> local_irq_save/restore() breaks IRQ state tracking -- see the reproducer >>>>>>>>> below. This is at least 1 case I can think of that we're bound to hit. >>>>>>> ... >>>>>>>> >>>>>>>> /me goes ponder things... >>>>>>>> >>>>>>>> How's something like this then? >>>>>>>> >>>>>>>> --- >>>>>>>> include/linux/sched.h | 3 --- >>>>>>>> kernel/kcsan/core.c | 62 ++++++++++++++++++++++++++++++++++++--------------- >>>>>>>> 2 files changed, 44 insertions(+), 21 deletions(-) >>>>>>> >>>>>>> Thank you! That approach seems to pass syzbot (also with >>>>>>> CONFIG_PARAVIRT) and kcsan-test tests. >>>>>>> >>>>>>> I had to modify it some, so that report.c's use of the restore logic >>>>>>> works and not mess up the IRQ trace printed on KCSAN reports (with >>>>>>> CONFIG_KCSAN_VERBOSE). >>>>>>> >>>>>>> I still need to fully convince myself all is well now and we don't end >>>>>>> up with more fixes. :-) If it passes further testing, I'll send it as a >>>>>>> real patch (I want to add you as Co-developed-by, but would need your >>>>>>> Signed-off-by for the code you pasted, I think.) >>>>> >>>>> I let it run on syzbot through the night, and it's fine without >>>>> PARAVIRT (see below). I have sent the patch (need your Signed-off-by >>>>> as it's based on your code, thank you!): >>>>> https://lkml.kernel.org/r/20200807090031.3506555-1-elver@google.com >>>>> >>>>>> With CONFIG_PARAVIRT=y (without the notrace->noinstr patch), I still >>>>>> get lockdep DEBUG_LOCKS_WARN_ON(!lockdep_hardirqs_enabled()), although >>>>>> it takes longer for syzbot to hit them. But I think that's expected >>>>>> because we can still get the recursion that I pointed out, and will >>>>>> need that patch. >>>>> >>>>> Never mind, I get these warnings even if I don't turn on KCSAN >>>>> (CONFIG_KCSAN=n). Something else is going on with PARAVIRT=y that >>>>> throws off IRQ state tracking. :-/ >>>> >>>> What are the settings of CONFIG_PARAVIRT_XXL and >>>> CONFIG_PARAVIRT_SPINLOCKS in this case? >>> >>> I attached a config. >>> >>> $> grep PARAVIRT .config >>> CONFIG_PARAVIRT=y >>> CONFIG_PARAVIRT_XXL=y >>> # CONFIG_PARAVIRT_DEBUG is not set >>> CONFIG_PARAVIRT_SPINLOCKS=y >>> # CONFIG_PARAVIRT_TIME_ACCOUNTING is not set >>> CONFIG_PARAVIRT_CLOCK=y >> >> Anything special I need to do to reproduce the problem? Or would you be >> willing to do some more rounds with different config settings? > > I can only test it with syzkaller, but that probably doesn't help if you > don't already have it set up. It can't seem to find a C reproducer. > > I did some more rounds with different configs. > >> I think CONFIG_PARAVIRT_XXL shouldn't matter, but I'm not completely >> sure about that. CONFIG_PARAVIRT_SPINLOCKS would be my primary suspect. > > Yes, PARAVIRT_XXL doesn't make a different. When disabling > PARAVIRT_SPINLOCKS, however, the warnings go away. Thanks for testing! I take it you are doing the tests in a KVM guest? If so I have a gut feeling that the use of local_irq_save() and local_irq_restore() in kvm_wait() might be fishy. I might be completely wrong here, though. BTW, I think Xen's variant of pv spinlocks is fine (no playing with IRQ on/off). Hyper-V seems to do the same as KVM, and kicking another vcpu could be problematic as well, as it is just using IPI. Juergen