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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 25A3EC433E0 for ; Tue, 11 Aug 2020 07:58:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EC2AF206B2 for ; Tue, 11 Aug 2020 07:57:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728277AbgHKH56 (ORCPT ); Tue, 11 Aug 2020 03:57:58 -0400 Received: from mx2.suse.de ([195.135.220.15]:59600 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726397AbgHKH56 (ORCPT ); Tue, 11 Aug 2020 03:57:58 -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 66B9BAB9F; Tue, 11 Aug 2020 07:58:17 +0000 (UTC) Subject: Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers To: Peter Zijlstra , Marco Elver Cc: 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" , Wei Liu References: <20200806131702.GA3029162@elver.google.com> <20200807095032.GA3528289@elver.google.com> <16671cf3-3885-eb06-79ff-4cbfaeeaea79@suse.com> <20200807113838.GA3547125@elver.google.com> <20200807151903.GA1263469@elver.google.com> <20200811074127.GR3982@worktop.programming.kicks-ass.net> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: Date: Tue, 11 Aug 2020 09:57:55 +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: <20200811074127.GR3982@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11.08.20 09:41, Peter Zijlstra wrote: > On Fri, Aug 07, 2020 at 05:19:03PM +0200, Marco Elver wrote: > >> My hypothesis here is simply that kvm_wait() may be called in a place >> where we get the same case I mentioned to Peter, >> >> raw_local_irq_save(); /* or other IRQs off without tracing */ >> ... >> kvm_wait() /* IRQ state tracing gets confused */ >> ... >> raw_local_irq_restore(); >> >> and therefore, using raw variants in kvm_wait() works. It's also safe >> because it doesn't call any other libraries that would result in corrupt > > Yes, this is definitely an issue. > > Tracing, we also musn't call into tracing when using raw_local_irq_*(). > Because then we re-intoduce this same issue all over again. > > Both halt() and safe_halt() are more paravirt calls, but given we're in > a KVM paravirt call already, I suppose we can directly use native_*() > here. > > Something like so then... I suppose, but then the Xen variants need TLC > too. Just to be sure I understand you correct: You mean that xen_qlock_kick() and xen_qlock_wait() and all functions called by those should gain the "notrace" attribute, right? I am not sure why the kick variants need it, though. IMO those are called only after the lock has been released, so they should be fine without notrace. And again: we shouldn't forget the Hyper-V variants. Juergen