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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id z11sm4163558pff.144.2021.09.16.14.41.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Sep 2021 14:41:04 -0700 (PDT) Date: Thu, 16 Sep 2021 21:41:01 +0000 From: Sean Christopherson To: Peter Zijlstra Subject: Re: [PATCH v2 01/13] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210828003558.713983-1-seanjc@google.com> <20210828003558.713983-2-seanjc@google.com> <20210828194421.GB4353@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210828194421.GB4353@worktop.programming.kicks-ass.net> X-Mailman-Approved-At: Fri, 17 Sep 2021 04:46:52 -0400 Cc: Wanpeng Li , kvm@vger.kernel.org, Alexander Shishkin , Catalin Marinas , Guo Ren , "H. Peter Anvin" , linux-riscv@lists.infradead.org, Vincent Chen , Jiri Olsa , Boris Ostrovsky , Stefano Stabellini , xen-devel@lists.xenproject.org, Marc Zyngier , Joerg Roedel , x86@kernel.org, linux-csky@vger.kernel.org, kvmarm@lists.cs.columbia.edu, Ingo Molnar , Like Xu , Albert Ou , Zhu Lingshan , Will Deacon , Arnaldo Carvalho de Melo , Borislav Petkov , Greentime Hu , Paul Walmsley , Namhyung Kim , Thomas Gleixner , Artem Kashkanov , linux-arm-kernel@lists.infradead.org, Jim Mattson , Juergen Gross , Nick Hu , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Palmer Dabbelt , Paolo Bonzini , Vitaly Kuznetsov X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Sat, Aug 28, 2021, Peter Zijlstra wrote: > On Fri, Aug 27, 2021 at 05:35:46PM -0700, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..2126f6327321 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,19 @@ struct perf_guest_info_callbacks *perf_guest_cbs; > > > > int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = cbs; > > + if (WARN_ON_ONCE(perf_guest_cbs)) > > + return -EBUSY; > > + > > + WRITE_ONCE(perf_guest_cbs, cbs); > > + synchronize_rcu(); > > You're waiting for all NULL users to go away? :-) IOW, we can do without > this synchronize_rcu() call. Doh, right. I was thinking KVM needed to wait for in-progress NMI to exit to ensure guest PT interrupts are handled correctly, but obviously the NMI handler needs to exit for that CPU to get into a guest... > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks); > > > > int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = NULL; > > if (WARN_ON_ONCE(perf_guest_cbs != cbs)) > return -EBUSY; > > ? Works for me. I guess I'm more optimistic about people not being morons :-) _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-18.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham 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 35229C433EF for ; Thu, 16 Sep 2021 21:41:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 199656120C for ; Thu, 16 Sep 2021 21:41:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235388AbhIPVm1 (ORCPT ); Thu, 16 Sep 2021 17:42:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34258 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234566AbhIPVm1 (ORCPT ); Thu, 16 Sep 2021 17:42:27 -0400 Received: from mail-pl1-x635.google.com (mail-pl1-x635.google.com [IPv6:2607:f8b0:4864:20::635]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 30CF7C061766 for ; Thu, 16 Sep 2021 14:41:06 -0700 (PDT) Received: by mail-pl1-x635.google.com with SMTP id n2so2182701plk.12 for ; Thu, 16 Sep 2021 14:41:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=H6MB2ODxA8ncTb3aji91NU1uUQ9q1AebxOl6ENeKyck=; b=MXQC+ZfLxlKAl3MhEJW1BaTu7x3eZBr25vDIOP4P1K/hKKNsBxR9bYAbQrcXeqx0IT UwrZDJawrFH60RbkF94BswFhIwo0cou0aN+gLacubbeU6IcTTMJrkdfHEYWn3Q3CVBfY FWOlqrCFMP2DA28EATBAk/sg6Cxl8pCwP9qJHgGrwzQTOnAwwW0mxDrD/8RBAtDi8Sen 7O4AbiMouCC1KnoWzOLrohcS9Vtb2Dd0sBl4eKlMlTi8+NrzRnGujJOfnGMsmwaTYUXB tHZDCMU2HvcsbXJF8DOiqaPVnBEOB3kiFk+1tNf5dSr4/Tt9/mMCbKmuD1xBAf0iTv/g rERQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=H6MB2ODxA8ncTb3aji91NU1uUQ9q1AebxOl6ENeKyck=; b=v5Ip/A+/fEvqqz14gV7tVvICaGhZEVmA8l34u8m2x6VqIHIWRD3lV4bisR2IGPD1Xa 7gpH2qiO0Q2+V9BFc/Bs3aKbMly3PTx/fFr+ZK+Y/rZyPukMJIP/OcDQuVhyy/f4KPZX tBrhPmVzNOaE1vxq4E+6ZtsQ26RK07RbNmyG1mgZ6VWUdsXRKt0CAGo2h6hiMQdZXzVz 2DhQaoiqre92O5vyITmzHZ048EDbGl0jGLyd84UzMiLicg8NQSrooXni49SXCCj7nVie OBOgDJcuWk/GXDoM4iul7RGChJXN0vxOIU6Bes8DFHqk+AQSDVlOR0jzrRIyMHgoVXYn wDyQ== X-Gm-Message-State: AOAM5315Nvy6wd1HiiDRwaX7b5B9e9vgB2YH/KMc91Cc5V63TkuDfM+S pcUKh1X0KNxw4K9l+Y2xlYstNg== X-Google-Smtp-Source: ABdhPJyEB8CLbdwiUNdfZdvrZtOKbQbkduopskaqSrtZd3BkA7cXNgyeY28844ULJzTSWyVMUXnICw== X-Received: by 2002:a17:903:244e:b0:13c:802d:92c with SMTP id l14-20020a170903244e00b0013c802d092cmr6486996pls.78.1631828465371; Thu, 16 Sep 2021 14:41:05 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id z11sm4163558pff.144.2021.09.16.14.41.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Sep 2021 14:41:04 -0700 (PDT) Date: Thu, 16 Sep 2021 21:41:01 +0000 From: Sean Christopherson To: Peter Zijlstra Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Will Deacon , Mark Rutland , Catalin Marinas , Marc Zyngier , Guo Ren , Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , x86@kernel.org, Paolo Bonzini , Boris Ostrovsky , Juergen Gross , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , "H. Peter Anvin" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-csky@vger.kernel.org, linux-riscv@lists.infradead.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, Artem Kashkanov , Like Xu , Zhu Lingshan Subject: Re: [PATCH v2 01/13] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210828003558.713983-1-seanjc@google.com> <20210828003558.713983-2-seanjc@google.com> <20210828194421.GB4353@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210828194421.GB4353@worktop.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org On Sat, Aug 28, 2021, Peter Zijlstra wrote: > On Fri, Aug 27, 2021 at 05:35:46PM -0700, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..2126f6327321 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,19 @@ struct perf_guest_info_callbacks *perf_guest_cbs; > > > > int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = cbs; > > + if (WARN_ON_ONCE(perf_guest_cbs)) > > + return -EBUSY; > > + > > + WRITE_ONCE(perf_guest_cbs, cbs); > > + synchronize_rcu(); > > You're waiting for all NULL users to go away? :-) IOW, we can do without > this synchronize_rcu() call. Doh, right. I was thinking KVM needed to wait for in-progress NMI to exit to ensure guest PT interrupts are handled correctly, but obviously the NMI handler needs to exit for that CPU to get into a guest... > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks); > > > > int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = NULL; > > if (WARN_ON_ONCE(perf_guest_cbs != cbs)) > return -EBUSY; > > ? Works for me. I guess I'm more optimistic about people not being morons :-) 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=-9.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_ADSP_CUSTOM_MED,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 3E39EC433F5 for ; Thu, 16 Sep 2021 21:41:24 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0867361206 for ; Thu, 16 Sep 2021 21:41:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0867361206 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=KnpBrTCNtAEFSV4gly7XTa+TgFwi838x8Duxjxsolvw=; b=xJuqjzXE+0SS36 I+eUyXXPeLskCcHeVspV2dPKDnn/V67TSsDRrdhkPk5AyTAp2DhXJzo9UasvyhctTbfOmSZXVdbbA mQnvXnPg3qSNwFm9td1LDyRp3IWL6Cvc6MugjkwLIioGEW+5zE8Gh/6RvEnwQhLtNjuUp+iuk70R3 qD1IxbnX5bHAo6fv7fF3YbKNAalMe2/iEFgvVvpDiG8SHjaLbmj0SNykfWBkIc4R1NswJog5p88dl PRK8fBkoYdZ7p/6snliV50eD27X4/GmNL0mBSgAQ8yOTapWp0nR0Mxo23XBFzTipynoctTOlPafxO iOdQgfx5CAVKDu1lvhNw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mQz82-00CQzH-2Q; Thu, 16 Sep 2021 21:41:10 +0000 Received: from mail-pl1-x62a.google.com ([2607:f8b0:4864:20::62a]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mQz7z-00CQxX-KF for linux-riscv@lists.infradead.org; Thu, 16 Sep 2021 21:41:09 +0000 Received: by mail-pl1-x62a.google.com with SMTP id v1so4758832plo.10 for ; Thu, 16 Sep 2021 14:41:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=H6MB2ODxA8ncTb3aji91NU1uUQ9q1AebxOl6ENeKyck=; b=MXQC+ZfLxlKAl3MhEJW1BaTu7x3eZBr25vDIOP4P1K/hKKNsBxR9bYAbQrcXeqx0IT UwrZDJawrFH60RbkF94BswFhIwo0cou0aN+gLacubbeU6IcTTMJrkdfHEYWn3Q3CVBfY FWOlqrCFMP2DA28EATBAk/sg6Cxl8pCwP9qJHgGrwzQTOnAwwW0mxDrD/8RBAtDi8Sen 7O4AbiMouCC1KnoWzOLrohcS9Vtb2Dd0sBl4eKlMlTi8+NrzRnGujJOfnGMsmwaTYUXB tHZDCMU2HvcsbXJF8DOiqaPVnBEOB3kiFk+1tNf5dSr4/Tt9/mMCbKmuD1xBAf0iTv/g rERQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=H6MB2ODxA8ncTb3aji91NU1uUQ9q1AebxOl6ENeKyck=; b=CcPQO2zI/k2/x6whxXgttsyFOxBhY0kRfsog82IV+/XJ+6w1ZNlgKfYOHJc099GQRY 50WzmATjbAGgXAWa1rhVpJRwtDZDcJ+63fT2BNWblzrtrhd2NW8kJZLW9zI0ANNMKguP TfVNMXUTD/ryb6Iaf3w/qI9u56Q2fzH7THU3I/5mxA8aS8Hi7hlA6/2uq4fLGqjLkp1e SvsPb+bXKPT2aQrkADQEiKrr9yPk2+nz29nZUGljN5n7q2mB7bWO3h3L9YNMgdL5dHIw FLX1ukm2PfifkFF0s/lC8nvoyVFrBwL6OUilHXhPnvkf2cksfoIHSqgP/Y1+JY/oQUsl LqJQ== X-Gm-Message-State: AOAM533zUzQe98Bl46zGarEweJrFPUXng1oRagTxZOYgdbQBifyCT0iT OJ+nLAiiG+coRZLh9/Mny2qgfw== X-Google-Smtp-Source: ABdhPJyEB8CLbdwiUNdfZdvrZtOKbQbkduopskaqSrtZd3BkA7cXNgyeY28844ULJzTSWyVMUXnICw== X-Received: by 2002:a17:903:244e:b0:13c:802d:92c with SMTP id l14-20020a170903244e00b0013c802d092cmr6486996pls.78.1631828465371; Thu, 16 Sep 2021 14:41:05 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id z11sm4163558pff.144.2021.09.16.14.41.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Sep 2021 14:41:04 -0700 (PDT) Date: Thu, 16 Sep 2021 21:41:01 +0000 From: Sean Christopherson To: Peter Zijlstra Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Will Deacon , Mark Rutland , Catalin Marinas , Marc Zyngier , Guo Ren , Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , x86@kernel.org, Paolo Bonzini , Boris Ostrovsky , Juergen Gross , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , "H. Peter Anvin" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-csky@vger.kernel.org, linux-riscv@lists.infradead.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, Artem Kashkanov , Like Xu , Zhu Lingshan Subject: Re: [PATCH v2 01/13] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210828003558.713983-1-seanjc@google.com> <20210828003558.713983-2-seanjc@google.com> <20210828194421.GB4353@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210828194421.GB4353@worktop.programming.kicks-ass.net> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210916_144107_698102_9FCBAD7C X-CRM114-Status: GOOD ( 17.06 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Sat, Aug 28, 2021, Peter Zijlstra wrote: > On Fri, Aug 27, 2021 at 05:35:46PM -0700, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..2126f6327321 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,19 @@ struct perf_guest_info_callbacks *perf_guest_cbs; > > > > int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = cbs; > > + if (WARN_ON_ONCE(perf_guest_cbs)) > > + return -EBUSY; > > + > > + WRITE_ONCE(perf_guest_cbs, cbs); > > + synchronize_rcu(); > > You're waiting for all NULL users to go away? :-) IOW, we can do without > this synchronize_rcu() call. Doh, right. I was thinking KVM needed to wait for in-progress NMI to exit to ensure guest PT interrupts are handled correctly, but obviously the NMI handler needs to exit for that CPU to get into a guest... > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks); > > > > int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = NULL; > > if (WARN_ON_ONCE(perf_guest_cbs != cbs)) > return -EBUSY; > > ? Works for me. I guess I'm more optimistic about people not being morons :-) _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv 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=-9.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_ADSP_CUSTOM_MED,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 658B3C433F5 for ; Thu, 16 Sep 2021 21:43:29 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2DC2F6120C for ; Thu, 16 Sep 2021 21:43:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 2DC2F6120C Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=DZxAWViFKE8+BB2rdh0GJctONxx9d/ZP0jf3cQy4ZEE=; b=KRh6v4Y+6jpkZn V4fkQXQNIP8ZGCnegj38yMfYUcSmgNpvJXgN8AAvCptyjzI/2BGAn01SwqH67pOwh2lJ7jcxB4c0u XvuAChWyP2X3NUy2Cfp2f7+zSxOmJI1z6VWJuLqEVEiTmg/BX0Qi7Kiy3k9td+mAGWY11VIsyUdfz FUJg4WeYS6wdof9VqIuxcqZhOfcnKWPgfdKZM8rtfcJRUXWPYRq/DpYa1A2pIPrCzjtDpVznVL0HJ /HXx9xwkKo7V82J6FpR9QFg9vj5gXZ49M+cf+02/zJHPaK6AbcJDq6AvszJwhSmsELo+KsWXll9dP +krpLKWM6OxpVec5/CeA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mQz84-00CR07-Na; Thu, 16 Sep 2021 21:41:12 +0000 Received: from mail-pj1-x102a.google.com ([2607:f8b0:4864:20::102a]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mQz7z-00CQxW-HN for linux-arm-kernel@lists.infradead.org; Thu, 16 Sep 2021 21:41:09 +0000 Received: by mail-pj1-x102a.google.com with SMTP id il14-20020a17090b164e00b0019c7a7c362dso2254526pjb.0 for ; Thu, 16 Sep 2021 14:41:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=H6MB2ODxA8ncTb3aji91NU1uUQ9q1AebxOl6ENeKyck=; b=MXQC+ZfLxlKAl3MhEJW1BaTu7x3eZBr25vDIOP4P1K/hKKNsBxR9bYAbQrcXeqx0IT UwrZDJawrFH60RbkF94BswFhIwo0cou0aN+gLacubbeU6IcTTMJrkdfHEYWn3Q3CVBfY FWOlqrCFMP2DA28EATBAk/sg6Cxl8pCwP9qJHgGrwzQTOnAwwW0mxDrD/8RBAtDi8Sen 7O4AbiMouCC1KnoWzOLrohcS9Vtb2Dd0sBl4eKlMlTi8+NrzRnGujJOfnGMsmwaTYUXB tHZDCMU2HvcsbXJF8DOiqaPVnBEOB3kiFk+1tNf5dSr4/Tt9/mMCbKmuD1xBAf0iTv/g rERQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=H6MB2ODxA8ncTb3aji91NU1uUQ9q1AebxOl6ENeKyck=; b=jCQ6VmQPcwlj0BhhE/wZa4c3DDZNUi15nOf/X0Jvk31i0gI8gXqfwfxyn71xp4VjP+ 9uuSQVfQpeB156DEQ5ttWzmQyn746emBgj6XeYkAHqLU62mVnBcYL49n3Ic/7VGSXU+b MuX86YlTVyDzIW5pMYIQIcoTuyYmxyWNJhLAb4RdVV0R3lS6hU4BgAeV8QNt4GGM+cSO IQZszZd8/9MfxaHLEJq8LiC5aOPlEbCPFwaCLR+cNBXJ57LDs4nAB0QYbg+W/NiA/yhZ v1LiFMB53GsayU5r99TXe83ISVtlZYOeFHQMAeLKEdQpzre3VYTwqHMboJIWFvWgLRqA nw3A== X-Gm-Message-State: AOAM531JscZXOv+tRoYr//1j4cd/0oD6SOK8immoqYCz9V3g7btn8BP2 R5vO0K6L0WjWOL1DBSbzLmEmdA== X-Google-Smtp-Source: ABdhPJyEB8CLbdwiUNdfZdvrZtOKbQbkduopskaqSrtZd3BkA7cXNgyeY28844ULJzTSWyVMUXnICw== X-Received: by 2002:a17:903:244e:b0:13c:802d:92c with SMTP id l14-20020a170903244e00b0013c802d092cmr6486996pls.78.1631828465371; Thu, 16 Sep 2021 14:41:05 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id z11sm4163558pff.144.2021.09.16.14.41.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Sep 2021 14:41:04 -0700 (PDT) Date: Thu, 16 Sep 2021 21:41:01 +0000 From: Sean Christopherson To: Peter Zijlstra Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Will Deacon , Mark Rutland , Catalin Marinas , Marc Zyngier , Guo Ren , Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , x86@kernel.org, Paolo Bonzini , Boris Ostrovsky , Juergen Gross , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , "H. Peter Anvin" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-csky@vger.kernel.org, linux-riscv@lists.infradead.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, Artem Kashkanov , Like Xu , Zhu Lingshan Subject: Re: [PATCH v2 01/13] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210828003558.713983-1-seanjc@google.com> <20210828003558.713983-2-seanjc@google.com> <20210828194421.GB4353@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210828194421.GB4353@worktop.programming.kicks-ass.net> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210916_144107_608005_92715E5B X-CRM114-Status: GOOD ( 18.44 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Aug 28, 2021, Peter Zijlstra wrote: > On Fri, Aug 27, 2021 at 05:35:46PM -0700, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..2126f6327321 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,19 @@ struct perf_guest_info_callbacks *perf_guest_cbs; > > > > int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = cbs; > > + if (WARN_ON_ONCE(perf_guest_cbs)) > > + return -EBUSY; > > + > > + WRITE_ONCE(perf_guest_cbs, cbs); > > + synchronize_rcu(); > > You're waiting for all NULL users to go away? :-) IOW, we can do without > this synchronize_rcu() call. Doh, right. I was thinking KVM needed to wait for in-progress NMI to exit to ensure guest PT interrupts are handled correctly, but obviously the NMI handler needs to exit for that CPU to get into a guest... > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks); > > > > int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > > { > > - perf_guest_cbs = NULL; > > if (WARN_ON_ONCE(perf_guest_cbs != cbs)) > return -EBUSY; > > ? Works for me. I guess I'm more optimistic about people not being morons :-) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel