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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id c9sm4061004pgq.58.2021.11.04.07.18.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Nov 2021 07:18:30 -0700 (PDT) Date: Thu, 4 Nov 2021 14:18:26 +0000 From: Sean Christopherson To: Like Xu Subject: Re: [PATCH v3 01/16] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210922000533.713300-1-seanjc@google.com> <20210922000533.713300-2-seanjc@google.com> <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> Cc: Wanpeng Li , kvm@vger.kernel.org, Peter Zijlstra , Guo Ren , linux-riscv@lists.infradead.org, Vincent Chen , Will Deacon , kvmarm@lists.cs.columbia.edu, Stefano Stabellini , Jiri Olsa , Joerg Roedel , linux-csky@vger.kernel.org, Alexander Shishkin , Ingo Molnar , xen-devel@lists.xenproject.org, Albert Ou , Zhu Lingshan , Arnaldo Carvalho de Melo , Greentime Hu , Paul Walmsley , Namhyung Kim , Boris Ostrovsky , 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 , Marc Zyngier , 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 Thu, Nov 04, 2021, Like Xu wrote: > On 22/9/2021 8:05 am, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..80ff050a7b55 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,21 @@ 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); > > So per Paolo's comment [1], does it help to use > smp_store_release(perf_guest_cbs, cbs) > or > rcu_assign_pointer(perf_guest_cbs, cbs) > here? Heh, if by "help" you mean "required to prevent bad things on weakly ordered architectures", then yes, it helps :-) If I'm interpeting Paolo's suggestion correctly, he's pointing out that oustanding stores to the function pointers in @cbs need to complete before assigning a non-NULL pointer to perf_guest_cbs, otherwise a perf event handler may see a valid pointer with half-baked callbacks. I think smp_store_release() with a comment would be appropriate, assuming my above interpretation is correct. > [1] https://lore.kernel.org/kvm/37afc465-c12f-01b9-f3b6-c2573e112d76@redhat.com/ > > > 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 -EINVAL; > > + > > + WRITE_ONCE(perf_guest_cbs, NULL); > > + synchronize_rcu(); > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks); > > _______________________________________________ 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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78C9EC433F5 for ; Thu, 4 Nov 2021 14:21:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 654FC611C0 for ; Thu, 4 Nov 2021 14:21:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232179AbhKDOYM (ORCPT ); Thu, 4 Nov 2021 10:24:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41462 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232095AbhKDOYJ (ORCPT ); Thu, 4 Nov 2021 10:24:09 -0400 Received: from mail-pg1-x52c.google.com (mail-pg1-x52c.google.com [IPv6:2607:f8b0:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2E65C09CE51 for ; Thu, 4 Nov 2021 07:18:31 -0700 (PDT) Received: by mail-pg1-x52c.google.com with SMTP id f5so5501480pgc.12 for ; Thu, 04 Nov 2021 07:18:31 -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=GgU1oUsck/kv7V8rA9YPXtLGsU5UGF/lzeg6fggjKVY=; b=RTR1r+Ui0w7nUSHbbKl234uth/uzF1T7qF0sliOvvfsRTTb+Ux1LBt/ffQdTAY+/ec E1O0cYaxUcP9JJO91gsHWRMciPl/F1cyjYk822jBCR9TBPiuByHH3wQyg8CO0RsG69s3 xxzxbxhqtVhFtR1IL3PwpUwYtMOSHDPFnwjUBiz3EACBzoEuXHLTOpHAkW6OfrqPvopQ XlcXyGEUw7b6wzkLr4K8OvDzbhOksbBNbi3EmpkiMJmFBXoGv87f+9auU+g0UJJslfkq YHd6yOra6jxs1gpwYkmD3+RM+zmhPNdO2qhY5Blp/Ql4/z42+YEAbgjAkELLYFLa2Wdb 1tBw== 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=GgU1oUsck/kv7V8rA9YPXtLGsU5UGF/lzeg6fggjKVY=; b=7ksxsnp3pdhGiayccES9wg+9UUFvvrbk/U9PzKJ/YTD/6i1EisBAMu02G+jaOGcPKu t535MhOprgv+lkj1RAhqDIl+vIFMYLJJoJv+x7Qila4UxFgiZ9bn/+uel+ogewqrkuQf 2L7niByHttfSJ61E/KnqSjD4BwnXvr2r5ngCy2GghNbVr4o27fQh6PVF36I6+GDGJIdU u0I1vI2dnImldwyHPAKS+dJy94yB5ldLw8HQm/Zi0AnCWjqB7CdMsWnemDnrljX0fFWW U9DDgvhIg2a9yaApHEvzPTvh6NKKrOQ1jBDByVvVFZQtR3cPR0ISnS1YRybPFS6LccGh AGCA== X-Gm-Message-State: AOAM532H9W3BtYcAfCqGw40ELz0RlEqzV3XJ/W6Nj/uvHTfiskGyoXJ6 jFH2GQfKLS2TMdEgrisM9lgOoQ== X-Google-Smtp-Source: ABdhPJxdt1yraCn5ATAvpc1jCPrfM/2fIu0pWDknNbK+x2XDbxsbKhM1gzBOeaAuduFP4pk+NDgWGQ== X-Received: by 2002:a65:5b01:: with SMTP id y1mr22260090pgq.451.1636035510920; Thu, 04 Nov 2021 07:18:30 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id c9sm4061004pgq.58.2021.11.04.07.18.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Nov 2021 07:18:30 -0700 (PDT) Date: Thu, 4 Nov 2021 14:18:26 +0000 From: Sean Christopherson To: Like Xu Cc: Peter Zijlstra , Will Deacon , Paolo Bonzini , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.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 , Zhu Lingshan , Juergen Gross , Ingo Molnar , Albert Ou , Palmer Dabbelt , Vincent Chen , Paul Walmsley , Greentime Hu , Boris Ostrovsky , Marc Zyngier , Nick Hu , Guo Ren , Mark Rutland , Arnaldo Carvalho de Melo Subject: Re: [PATCH v3 01/16] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210922000533.713300-1-seanjc@google.com> <20210922000533.713300-2-seanjc@google.com> <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org On Thu, Nov 04, 2021, Like Xu wrote: > On 22/9/2021 8:05 am, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..80ff050a7b55 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,21 @@ 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); > > So per Paolo's comment [1], does it help to use > smp_store_release(perf_guest_cbs, cbs) > or > rcu_assign_pointer(perf_guest_cbs, cbs) > here? Heh, if by "help" you mean "required to prevent bad things on weakly ordered architectures", then yes, it helps :-) If I'm interpeting Paolo's suggestion correctly, he's pointing out that oustanding stores to the function pointers in @cbs need to complete before assigning a non-NULL pointer to perf_guest_cbs, otherwise a perf event handler may see a valid pointer with half-baked callbacks. I think smp_store_release() with a comment would be appropriate, assuming my above interpretation is correct. > [1] https://lore.kernel.org/kvm/37afc465-c12f-01b9-f3b6-c2573e112d76@redhat.com/ > > > 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 -EINVAL; > > + > > + WRITE_ONCE(perf_guest_cbs, NULL); > > + synchronize_rcu(); > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks); > > 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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ACCE6C433EF for ; Thu, 4 Nov 2021 14:19:04 +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 6AC1C610FD for ; Thu, 4 Nov 2021 14:19:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6AC1C610FD 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=j3/2Ons7WJxIdc64nIP5rRQ3gFphD6thm94LFrRmWwY=; b=P9xSLz/dYcY2E5 e5P8XHw4JqUMp7fPm4zeRPlHYa14MXPbrTG93DDigJwM22W8enAWueg2Goe62NiRLy8A5PxblBZbw Q7lFsaMgFFLsn39X/dKG8iWZPEveXlju/eLn+DwCuo8jx7aWlC3GSqmr4HMpVv5HrgeGv5Zlh6ZbJ J570WBjqu1TJdf1JMgXPnxVFwItVc7WceC1EyQJWTypmCeLOWrXbfW4Ds6xFnTXEeqw251BU1scgF D+zlZvI4ZcPzVUfBmIHl6dpIAp6Pr3Jyu0GXa56kOcemx8h+Y+A6E85p08hDm+SDcyBMavl5Xxl09 eVOz5I56GWkO3KgbjhYA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1midZq-0095t8-VV; Thu, 04 Nov 2021 14:18:50 +0000 Received: from mail-pf1-x42a.google.com ([2607:f8b0:4864:20::42a]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1midZd-0095qg-IE for linux-riscv@lists.infradead.org; Thu, 04 Nov 2021 14:18:39 +0000 Received: by mail-pf1-x42a.google.com with SMTP id n85so1500582pfd.10 for ; Thu, 04 Nov 2021 07:18:31 -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=GgU1oUsck/kv7V8rA9YPXtLGsU5UGF/lzeg6fggjKVY=; b=RTR1r+Ui0w7nUSHbbKl234uth/uzF1T7qF0sliOvvfsRTTb+Ux1LBt/ffQdTAY+/ec E1O0cYaxUcP9JJO91gsHWRMciPl/F1cyjYk822jBCR9TBPiuByHH3wQyg8CO0RsG69s3 xxzxbxhqtVhFtR1IL3PwpUwYtMOSHDPFnwjUBiz3EACBzoEuXHLTOpHAkW6OfrqPvopQ XlcXyGEUw7b6wzkLr4K8OvDzbhOksbBNbi3EmpkiMJmFBXoGv87f+9auU+g0UJJslfkq YHd6yOra6jxs1gpwYkmD3+RM+zmhPNdO2qhY5Blp/Ql4/z42+YEAbgjAkELLYFLa2Wdb 1tBw== 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=GgU1oUsck/kv7V8rA9YPXtLGsU5UGF/lzeg6fggjKVY=; b=QOr0wmUWCdkj6hp4AvBqin4IsVaOg7RlN5XdupO82td1WJ7y9yNtalhUGQYi/ILYlm yqLY5V2g/5wrsiGb+JvHtr6IFD3nV+3kCRJyh8Lf3x1wva2z9d1buPHptzNR3Ibh5B5I Tu3gxAsFJo7/JG+6CG3NV2+wVNF6iuO2kTwmlC4kgv9zR2xf7udOIcakmaMQqkMagqB1 vZVOfamIvey9914xiKAAd1auhE8MPlov4ZzNYAkwtGR5VGAUFLUh9vVHcIZXWgU+XZsy QyCXNKDhoWEkvcNT+0Q+Tbt98Samv/24OPu6nRTLprE5deWw3Fe3rp142XdH62jAriu8 hodw== X-Gm-Message-State: AOAM531zZPqzAPPuYHi6CJPPgVtQ9iyKwq4pO3f8jBx+l9evwLqvbmNR R+hy3JJfe8M+M7lgD5lIZRAEOg== X-Google-Smtp-Source: ABdhPJxdt1yraCn5ATAvpc1jCPrfM/2fIu0pWDknNbK+x2XDbxsbKhM1gzBOeaAuduFP4pk+NDgWGQ== X-Received: by 2002:a65:5b01:: with SMTP id y1mr22260090pgq.451.1636035510920; Thu, 04 Nov 2021 07:18:30 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id c9sm4061004pgq.58.2021.11.04.07.18.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Nov 2021 07:18:30 -0700 (PDT) Date: Thu, 4 Nov 2021 14:18:26 +0000 From: Sean Christopherson To: Like Xu Cc: Peter Zijlstra , Will Deacon , Paolo Bonzini , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.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 , Zhu Lingshan , Juergen Gross , Ingo Molnar , Albert Ou , Palmer Dabbelt , Vincent Chen , Paul Walmsley , Greentime Hu , Boris Ostrovsky , Marc Zyngier , Nick Hu , Guo Ren , Mark Rutland , Arnaldo Carvalho de Melo Subject: Re: [PATCH v3 01/16] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210922000533.713300-1-seanjc@google.com> <20210922000533.713300-2-seanjc@google.com> <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211104_071837_636362_BABA754F X-CRM114-Status: GOOD ( 15.95 ) 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 Thu, Nov 04, 2021, Like Xu wrote: > On 22/9/2021 8:05 am, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..80ff050a7b55 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,21 @@ 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); > > So per Paolo's comment [1], does it help to use > smp_store_release(perf_guest_cbs, cbs) > or > rcu_assign_pointer(perf_guest_cbs, cbs) > here? Heh, if by "help" you mean "required to prevent bad things on weakly ordered architectures", then yes, it helps :-) If I'm interpeting Paolo's suggestion correctly, he's pointing out that oustanding stores to the function pointers in @cbs need to complete before assigning a non-NULL pointer to perf_guest_cbs, otherwise a perf event handler may see a valid pointer with half-baked callbacks. I think smp_store_release() with a comment would be appropriate, assuming my above interpretation is correct. > [1] https://lore.kernel.org/kvm/37afc465-c12f-01b9-f3b6-c2573e112d76@redhat.com/ > > > 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 -EINVAL; > > + > > + WRITE_ONCE(perf_guest_cbs, NULL); > > + synchronize_rcu(); > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks); > > _______________________________________________ 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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1DA3BC433F5 for ; Thu, 4 Nov 2021 14:20:33 +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 CF9FC611C1 for ; Thu, 4 Nov 2021 14:20:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org CF9FC611C1 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=eZQpoaB+lI1kqdN907tRWOiywtbdhkwHQewJ6LlQa5o=; b=TJ85etwAosGRN2 qEOM/Jyc4H8vWNmnR88ElFBG62tfoCc9Fk3PNDvY+XbRzKG1ZeDRai6EwXsUP+VOsQnWnSf+ZmYKh KHpq2z+8oGZzk77CNfWMmJbxzVxsIg+8sxqZesfhzH88ge+to/qJkcKq1Hj0lOxcUyUu5CUG3etja ak+j6THbNGiaS/ZPPJ2KOMTnG05A3pE1xKo51L8eK0afZ+FXdd60PFQl9LmhnKgSS+hDywoGLAxs8 WQnh4km/D4GVmhFk1t8WuHdlbz2mHNLnNTWhzHUJYRF1k2O3AumEtSMU/kUFr6bNT716R3PepogBz qAWZ97ywDKXyFlPlDQLw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1midZh-0095ra-Qz; Thu, 04 Nov 2021 14:18:42 +0000 Received: from mail-pg1-x530.google.com ([2607:f8b0:4864:20::530]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1midZd-0095qf-IW for linux-arm-kernel@lists.infradead.org; Thu, 04 Nov 2021 14:18:39 +0000 Received: by mail-pg1-x530.google.com with SMTP id p8so4203393pgh.11 for ; Thu, 04 Nov 2021 07:18:31 -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=GgU1oUsck/kv7V8rA9YPXtLGsU5UGF/lzeg6fggjKVY=; b=RTR1r+Ui0w7nUSHbbKl234uth/uzF1T7qF0sliOvvfsRTTb+Ux1LBt/ffQdTAY+/ec E1O0cYaxUcP9JJO91gsHWRMciPl/F1cyjYk822jBCR9TBPiuByHH3wQyg8CO0RsG69s3 xxzxbxhqtVhFtR1IL3PwpUwYtMOSHDPFnwjUBiz3EACBzoEuXHLTOpHAkW6OfrqPvopQ XlcXyGEUw7b6wzkLr4K8OvDzbhOksbBNbi3EmpkiMJmFBXoGv87f+9auU+g0UJJslfkq YHd6yOra6jxs1gpwYkmD3+RM+zmhPNdO2qhY5Blp/Ql4/z42+YEAbgjAkELLYFLa2Wdb 1tBw== 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=GgU1oUsck/kv7V8rA9YPXtLGsU5UGF/lzeg6fggjKVY=; b=GuionUyXG3bkJvCKqEtMAkxttQuOAQOMNRflzF/kX6bosox1EywJa0hgHIIxTKAxuA DXzs4D7BIxyF9NvJ2FuG4lKgB1KR5iMazcDX5gyAytul5A8xT9t7KSKGQU8EUYpxmo0e 584Xdb4JAkeYROq3fGyQwqBlBclRvrEMweJzIrBIgdathi/eel22+sLygrg/Khuj90ld fR0LxNNJ+X8O8xjF7OtRzdSrPA3RaF6DaucLRRWnEJowcsVd9xzrht4qf1nn5FBSUuOQ z4koK9dKA896XwpKxP36tVXWDRRto8bAYq1dh7dN5BdaDMLpV2uJ0kGiZhybHiTjCbAB ipOA== X-Gm-Message-State: AOAM533KoIlDQuPbb9X5ufgOjw9ZbMeEV9PhT1LspLjO7t3g3RQ2I//S uvao8XHrjldkfzuTK5ZXIfWUWA== X-Google-Smtp-Source: ABdhPJxdt1yraCn5ATAvpc1jCPrfM/2fIu0pWDknNbK+x2XDbxsbKhM1gzBOeaAuduFP4pk+NDgWGQ== X-Received: by 2002:a65:5b01:: with SMTP id y1mr22260090pgq.451.1636035510920; Thu, 04 Nov 2021 07:18:30 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id c9sm4061004pgq.58.2021.11.04.07.18.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Nov 2021 07:18:30 -0700 (PDT) Date: Thu, 4 Nov 2021 14:18:26 +0000 From: Sean Christopherson To: Like Xu Cc: Peter Zijlstra , Will Deacon , Paolo Bonzini , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.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 , Zhu Lingshan , Juergen Gross , Ingo Molnar , Albert Ou , Palmer Dabbelt , Vincent Chen , Paul Walmsley , Greentime Hu , Boris Ostrovsky , Marc Zyngier , Nick Hu , Guo Ren , Mark Rutland , Arnaldo Carvalho de Melo Subject: Re: [PATCH v3 01/16] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref Message-ID: References: <20210922000533.713300-1-seanjc@google.com> <20210922000533.713300-2-seanjc@google.com> <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <77e3a76a-016b-8945-a1d5-aae4075e2147@gmail.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211104_071837_638308_9252FC60 X-CRM114-Status: GOOD ( 17.43 ) 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 Thu, Nov 04, 2021, Like Xu wrote: > On 22/9/2021 8:05 am, Sean Christopherson wrote: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 464917096e73..80ff050a7b55 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6491,14 +6491,21 @@ 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); > > So per Paolo's comment [1], does it help to use > smp_store_release(perf_guest_cbs, cbs) > or > rcu_assign_pointer(perf_guest_cbs, cbs) > here? Heh, if by "help" you mean "required to prevent bad things on weakly ordered architectures", then yes, it helps :-) If I'm interpeting Paolo's suggestion correctly, he's pointing out that oustanding stores to the function pointers in @cbs need to complete before assigning a non-NULL pointer to perf_guest_cbs, otherwise a perf event handler may see a valid pointer with half-baked callbacks. I think smp_store_release() with a comment would be appropriate, assuming my above interpretation is correct. > [1] https://lore.kernel.org/kvm/37afc465-c12f-01b9-f3b6-c2573e112d76@redhat.com/ > > > 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 -EINVAL; > > + > > + WRITE_ONCE(perf_guest_cbs, NULL); > > + synchronize_rcu(); > > return 0; > > } > > EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks); > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel