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Peter Anvin" , Andy Lutomirski , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Paolo Bonzini , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Mingwei Zhang , Xudong Hao , Sandipan Das , Dapeng Mi , Xiong Zhang , Manali Shukla , Jim Mattson X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251208_100800_905510_3A5E1B45 X-CRM114-Status: GOOD ( 18.39 ) X-BeenThere: kvm-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: "kvm-riscv" Errors-To: kvm-riscv-bounces+kvm-riscv=archiver.kernel.org@lists.infradead.org On Mon, Dec 08, 2025, Peter Zijlstra wrote: > On Fri, Dec 05, 2025 at 04:16:40PM -0800, Sean Christopherson wrote: > > > +static atomic_t nr_include_guest_events __read_mostly; > > + > > +static atomic_t nr_mediated_pmu_vms __read_mostly; > > +static DEFINE_MUTEX(perf_mediated_pmu_mutex); > > > +static int mediated_pmu_account_event(struct perf_event *event) > > +{ > > + if (!is_include_guest_event(event)) > > + return 0; > > + > > + guard(mutex)(&perf_mediated_pmu_mutex); > > + > > + if (atomic_read(&nr_mediated_pmu_vms)) > > + return -EOPNOTSUPP; > > + > > + atomic_inc(&nr_include_guest_events); > > + return 0; > > +} > > + > > +static void mediated_pmu_unaccount_event(struct perf_event *event) > > +{ > > + if (!is_include_guest_event(event)) > > + return; > > + > > + atomic_dec(&nr_include_guest_events); > > +} > > > +int perf_create_mediated_pmu(void) > > +{ > > + guard(mutex)(&perf_mediated_pmu_mutex); > > + if (atomic_inc_not_zero(&nr_mediated_pmu_vms)) > > + return 0; > > + > > + if (atomic_read(&nr_include_guest_events)) > > + return -EBUSY; > > + > > + atomic_inc(&nr_mediated_pmu_vms); > > + return 0; > > +} > > +EXPORT_SYMBOL_GPL(perf_create_mediated_pmu); > > + > > +void perf_release_mediated_pmu(void) > > +{ > > + if (WARN_ON_ONCE(!atomic_read(&nr_mediated_pmu_vms))) > > + return; > > + > > + atomic_dec(&nr_mediated_pmu_vms); > > +} > > +EXPORT_SYMBOL_GPL(perf_release_mediated_pmu); > > These two things are supposed to be symmetric, but are implemented > differently; what gives? > > That is, should not both have the general shape: > > if (atomic_inc_not_zero(&A)) > return 0; > > guard(mutex)(&lock); > > if (atomic_read(&B)) > return -EBUSY; > > atomic_inc(&A); > return 0; > > Similarly, I would imagine both release variants to have the underflow > warn on like: > > if (WARN_ON_ONCE(!atomic_read(&A))) > return; > > atomic_dec(&A); > > Hmm? IIUC, you're suggesting someting like this? If so, that makes perfect sense to me. diff --git a/kernel/events/core.c b/kernel/events/core.c index c6368c64b866..fa2e7b722283 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6356,7 +6356,8 @@ static int mediated_pmu_account_event(struct perf_event *event) static void mediated_pmu_unaccount_event(struct perf_event *event) { - if (!is_include_guest_event(event)) + if (!is_include_guest_event(event) || + WARN_ON_ONCE(!atomic_read(&nr_include_guest_events))) return; atomic_dec(&nr_include_guest_events); > Also, EXPORT_SYMBOL_FOR_KVM() ? Ya, for sure. I posted this against a branch without EXPORT_SYMBOL_FOR_KVM(), because there are also hard dependencies on the for-6.19 KVM pull requests, and I didn't want to wait to post until 6.19-rc1 because of the impending winter break. Though I also simply forgot about these exports :-( These could also use EXPORT_SYMBOL_FOR_KVM(): EXPORT_SYMBOL_FOR_MODULES(perf_load_guest_lvtpc, "kvm"); EXPORT_SYMBOL_FOR_MODULES(perf_put_guest_lvtpc, "kvm"); > I can make these edits when applying, if/when we get to applying. Let me > continue reading. > -- kvm-riscv mailing list kvm-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kvm-riscv From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CBD0C226CFD for ; Mon, 8 Dec 2025 18:07:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765217281; cv=none; b=psrguMvE310ntsfmusPW/yynNkvCpYC7S2xijiBL6f4i32GRbjcmYajqPCqsKJjIV3wBqi1YpalkbjgoHYFA2PxFT5RPmwSTfCPjV1mu2gsfGovRzwMfpm7KnjMdB3soMy0CqsCATU9vfEE0cgv99MjIWFyPsmfVoP+YuZ6Q99U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765217281; c=relaxed/simple; bh=9iufsu/WFJNy0WogHro7btB7qYSuDu2TmGiNlbbFqhw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Bnv//YdDUKwzNZUuDVLrVE+kVj1Ik+pqotbrxllM2GIFvRskcd1CZm7qvA1C/2GqCv2rOLeYNaA7uGzVJHHD//hOHUpt/utVHxEJW7TK32k0N3rgoXHojsCvBlK6x5O/9vQVD2gDDZdAODVm8BPcncsCEWLwHYAgTNxzfhIvTIY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=vE1l1i6A; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="vE1l1i6A" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-340c261fb38so8127158a91.0 for ; Mon, 08 Dec 2025 10:07:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1765217279; x=1765822079; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=SF6h5hGtRuMyBRglBJmpKQuSrVGlyuxXyhedVebSd6M=; b=vE1l1i6Aly2WBn1u85OnmHHA+4/1tuppegXDLfZHeS8tcHZSqO9X0mwCzSQ3uZsObZ HTrtBphv7J9Ip5Vjo80q7RXXw6Z1CWx0agvmWnGHj4PJZmqAnMan4zx+6vtFRMRoUD4b xJNOghHYVnZbGgyQ/VhtBoksP2o3J6mb9WqHV/Edy25cQ4ekaGB81pNYWE44oDto76Vl cxgRoJkiF7AmYD4Is4m++XyrkqVzbifQj+dVzehI3YfJuQ9EgbezxWuxuViAixmXQAkZ UTBf3hBZz58dRQ33Ev4GSN4H8yIXoc8lYJypWdpbegTO5ioaaN9AjLktovI8AFvv0Q3Y FTNQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765217279; x=1765822079; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=SF6h5hGtRuMyBRglBJmpKQuSrVGlyuxXyhedVebSd6M=; b=dek4PbKcJm3ftBiQKA1YH9GUUG4KCmyeiPuYExpGwZs2NqRAoiUcvQF7t6ZqBILERP 7S/cPNmkP5BjGibCVxtFZWRU6CzPWx1ZbcuCp1OnmUDkqkWEBdWhYuMDfLf/1jE11mu7 BKmWbD1dJ0kTCsAkmSBsIIMCFYR9cCgstHBB4HjTC8V1ZXmyErFGNPclvXWt1gnik+I5 ewxYp0neW09MT9RlMT6tKWzJPBx1FwWfy79eplFQrJB6nEXu/Hzew2uu6cJTcxZbqOwz WzB/ocuUgspFAd7xODWVJavfBJCWOUsUnNvuGyAha7JT6nZPHXR3/VclBNoutMM4fyPg B1Wg== X-Forwarded-Encrypted: i=1; AJvYcCWiklCuSbVNqkUpmaQwkRi4vAPT5FMxu82H1in9BZBi9mgSSxOlXFfUEuXepjUhGqyfIw0=@vger.kernel.org X-Gm-Message-State: AOJu0Yy6L/wJYYVKlKv9h4YkKRUXs6nHTZJc6lQEqiybyP6NnyjDIxSE f+Qgr+kV8l9ZnXboJ+qNB7zlTinYlGM8Tpf0NWWet4MfANj2I52u2UQrdeqF90/bxnqUZ1AlJIk wKUjjyQ== X-Google-Smtp-Source: AGHT+IH3HhOiXlRek80ArMNgo8utGCkumZ6GCHftobZYLKaRSJ46MkO0EFccaQp1M2wj9T7xKajFvZIZ67U= X-Received: from pjbfs21.prod.google.com ([2002:a17:90a:f295:b0:343:6849:31ae]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2787:b0:349:8a8b:da5c with SMTP id 98e67ed59e1d1-349a24f2f71mr7253927a91.11.1765217279160; Mon, 08 Dec 2025 10:07:59 -0800 (PST) Date: Mon, 8 Dec 2025 10:07:57 -0800 In-Reply-To: <20251208115156.GE3707891@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251206001720.468579-1-seanjc@google.com> <20251206001720.468579-5-seanjc@google.com> <20251208115156.GE3707891@noisy.programming.kicks-ass.net> Message-ID: Subject: Re: [PATCH v6 04/44] perf: Add APIs to create/release mediated guest vPMUs From: Sean Christopherson To: Peter Zijlstra Cc: Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Xin Li , "H. Peter Anvin" , Andy Lutomirski , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Paolo Bonzini , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Mingwei Zhang , Xudong Hao , Sandipan Das , Dapeng Mi , Xiong Zhang , Manali Shukla , Jim Mattson Content-Type: text/plain; charset="us-ascii" On Mon, Dec 08, 2025, Peter Zijlstra wrote: > On Fri, Dec 05, 2025 at 04:16:40PM -0800, Sean Christopherson wrote: > > > +static atomic_t nr_include_guest_events __read_mostly; > > + > > +static atomic_t nr_mediated_pmu_vms __read_mostly; > > +static DEFINE_MUTEX(perf_mediated_pmu_mutex); > > > +static int mediated_pmu_account_event(struct perf_event *event) > > +{ > > + if (!is_include_guest_event(event)) > > + return 0; > > + > > + guard(mutex)(&perf_mediated_pmu_mutex); > > + > > + if (atomic_read(&nr_mediated_pmu_vms)) > > + return -EOPNOTSUPP; > > + > > + atomic_inc(&nr_include_guest_events); > > + return 0; > > +} > > + > > +static void mediated_pmu_unaccount_event(struct perf_event *event) > > +{ > > + if (!is_include_guest_event(event)) > > + return; > > + > > + atomic_dec(&nr_include_guest_events); > > +} > > > +int perf_create_mediated_pmu(void) > > +{ > > + guard(mutex)(&perf_mediated_pmu_mutex); > > + if (atomic_inc_not_zero(&nr_mediated_pmu_vms)) > > + return 0; > > + > > + if (atomic_read(&nr_include_guest_events)) > > + return -EBUSY; > > + > > + atomic_inc(&nr_mediated_pmu_vms); > > + return 0; > > +} > > +EXPORT_SYMBOL_GPL(perf_create_mediated_pmu); > > + > > +void perf_release_mediated_pmu(void) > > +{ > > + if (WARN_ON_ONCE(!atomic_read(&nr_mediated_pmu_vms))) > > + return; > > + > > + atomic_dec(&nr_mediated_pmu_vms); > > +} > > +EXPORT_SYMBOL_GPL(perf_release_mediated_pmu); > > These two things are supposed to be symmetric, but are implemented > differently; what gives? > > That is, should not both have the general shape: > > if (atomic_inc_not_zero(&A)) > return 0; > > guard(mutex)(&lock); > > if (atomic_read(&B)) > return -EBUSY; > > atomic_inc(&A); > return 0; > > Similarly, I would imagine both release variants to have the underflow > warn on like: > > if (WARN_ON_ONCE(!atomic_read(&A))) > return; > > atomic_dec(&A); > > Hmm? IIUC, you're suggesting someting like this? If so, that makes perfect sense to me. diff --git a/kernel/events/core.c b/kernel/events/core.c index c6368c64b866..fa2e7b722283 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6356,7 +6356,8 @@ static int mediated_pmu_account_event(struct perf_event *event) static void mediated_pmu_unaccount_event(struct perf_event *event) { - if (!is_include_guest_event(event)) + if (!is_include_guest_event(event) || + WARN_ON_ONCE(!atomic_read(&nr_include_guest_events))) return; atomic_dec(&nr_include_guest_events); > Also, EXPORT_SYMBOL_FOR_KVM() ? Ya, for sure. I posted this against a branch without EXPORT_SYMBOL_FOR_KVM(), because there are also hard dependencies on the for-6.19 KVM pull requests, and I didn't want to wait to post until 6.19-rc1 because of the impending winter break. Though I also simply forgot about these exports :-( These could also use EXPORT_SYMBOL_FOR_KVM(): EXPORT_SYMBOL_FOR_MODULES(perf_load_guest_lvtpc, "kvm"); EXPORT_SYMBOL_FOR_MODULES(perf_put_guest_lvtpc, "kvm"); > I can make these edits when applying, if/when we get to applying. Let me > continue reading. > 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id D73D5D3B7EA for ; Mon, 8 Dec 2025 18:08:16 +0000 (UTC) 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:Cc:To:From:Subject:Message-ID: References:Mime-Version:In-Reply-To:Date:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=kI/jvDJA0hB07R/0VZyQVxwFJnEzhG3DJYbizqxAyxo=; b=P+46jqz0+BOe9twYUkdcmd6aeP K1Uag0S+W9hw95GNkT1fDZbeschrDsET6+/N/3e7KEIheO0amMLmBWIT5/cUkbzXN1leYmLOFJDbP C70xBEKLsHxm3+XD4VQh1aixICltfeK+MQRHVyHXt1tH1gwpBsmlThgc3Z6OVhioF0OD/vROn+LXL nRgaJOazgprETLHuDbWvesb1Cz7BSKd2MEgJmzynOpY5Uh7RBU82PUiQl/IrRzu5tKhgoX8a9rBs6 G2P7X9GBjZSUy6leAmqSCX85JRkqpJP15jMCDAR8ngvT/ldRx0eFAWwT/VAbhi51fFNCR2AkMTKtB LhyKxr6g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vSfeV-0000000DPtR-1UeQ; Mon, 08 Dec 2025 18:08:03 +0000 Received: from mail-pj1-x104a.google.com ([2607:f8b0:4864:20::104a]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vSfeS-0000000DPsL-31xn for linux-riscv@lists.infradead.org; Mon, 08 Dec 2025 18:08:01 +0000 Received: by mail-pj1-x104a.google.com with SMTP id 98e67ed59e1d1-349a2f509acso4008291a91.1 for ; Mon, 08 Dec 2025 10:07:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1765217279; x=1765822079; darn=lists.infradead.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=SF6h5hGtRuMyBRglBJmpKQuSrVGlyuxXyhedVebSd6M=; b=rY2uZbqVR52TSP72znPUL8jA5ul05kEze0XOV1OIIlCaQXC6HmuBPUsznpSlU8w42+ mFzVS72bLZV20Jbz+sbfdSzukqigPAasmS7l3gnyDIe2IISJhRpzBTz3Xno5fKF9HaUS 8WY9ZXiQNkmW6bPeDv7XPu9iDQ4P+7/P48gjLaixWLGXUj4u5bTaC6K/+Cv0Vf2NDKXQ YtLcF5eF1l1tXca9mnz86QfpWZOsgPL880wag/ZOqmhKIiUp4HC9PqkA1XHxMdhHkbPF uRO0ZlYisFpHEheeyullDxyozIdy3+x+29jnPbwMAsuO2J+izI3HPVI7YsLalDbGHKD+ f4hg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765217279; x=1765822079; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=SF6h5hGtRuMyBRglBJmpKQuSrVGlyuxXyhedVebSd6M=; b=j8q8I+n+kRuGo+BTmWedKKut1IBfPDlcyN6hcpkAqZmnxKn23vKB8/YHzicMHZs/e9 e+zg1xBanVBWdRx4z5lgDPJdhIO14hqW+4ocDdnlYMcaZivxXDnj7a2XhyjWQwzr0cWZ iCixhHF1+l4wO7HZ/lZ4FoA/QFAtAVJCwyb6/NhG01bKINPpMxdEvR3GX2GK/c4h+aB8 xpWPkjqJ9qfiBhBk4r6VJU4fVLcdoRxRYd6931rLebEaAL2PfVbYNX/+EoGffXvB8seb Ju+uoz3G9tR885QG3rzlfpZGVtJKwPOD/lxLm79FcrllPExWvXZIPg9JCrW10fLS1XUK duog== X-Forwarded-Encrypted: i=1; AJvYcCV/3oee/9tJ1pwPiezrBr+ihBpabYqtAFwt+9LI9yVwdgmaHzlToLFA8C+09joDHj4l7v2OvPfKrc3iHQ==@lists.infradead.org X-Gm-Message-State: AOJu0Yxweucd5Rm7bvoLHVUV5Il/LkFXkb0IuF4PC+RXfaq3/c+jjGCY 29BUoI2en0J78hlr+FkXMEqtUPq0+fzI7B4QLik+AZ4e+6U2hK8rg1P1g9a6GTd/1P2g1feCL+A 2jr68cw== X-Google-Smtp-Source: AGHT+IH3HhOiXlRek80ArMNgo8utGCkumZ6GCHftobZYLKaRSJ46MkO0EFccaQp1M2wj9T7xKajFvZIZ67U= X-Received: from pjbfs21.prod.google.com ([2002:a17:90a:f295:b0:343:6849:31ae]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2787:b0:349:8a8b:da5c with SMTP id 98e67ed59e1d1-349a24f2f71mr7253927a91.11.1765217279160; Mon, 08 Dec 2025 10:07:59 -0800 (PST) Date: Mon, 8 Dec 2025 10:07:57 -0800 In-Reply-To: <20251208115156.GE3707891@noisy.programming.kicks-ass.net> Mime-Version: 1.0 References: <20251206001720.468579-1-seanjc@google.com> <20251206001720.468579-5-seanjc@google.com> <20251208115156.GE3707891@noisy.programming.kicks-ass.net> Message-ID: Subject: Re: [PATCH v6 04/44] perf: Add APIs to create/release mediated guest vPMUs From: Sean Christopherson To: Peter Zijlstra Cc: Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Xin Li , "H. Peter Anvin" , Andy Lutomirski , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Paolo Bonzini , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Mingwei Zhang , Xudong Hao , Sandipan Das , Dapeng Mi , Xiong Zhang , Manali Shukla , Jim Mattson X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251208_100800_755913_3B7CFCD8 X-CRM114-Status: GOOD ( 18.39 ) 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 Mon, Dec 08, 2025, Peter Zijlstra wrote: > On Fri, Dec 05, 2025 at 04:16:40PM -0800, Sean Christopherson wrote: > > > +static atomic_t nr_include_guest_events __read_mostly; > > + > > +static atomic_t nr_mediated_pmu_vms __read_mostly; > > +static DEFINE_MUTEX(perf_mediated_pmu_mutex); > > > +static int mediated_pmu_account_event(struct perf_event *event) > > +{ > > + if (!is_include_guest_event(event)) > > + return 0; > > + > > + guard(mutex)(&perf_mediated_pmu_mutex); > > + > > + if (atomic_read(&nr_mediated_pmu_vms)) > > + return -EOPNOTSUPP; > > + > > + atomic_inc(&nr_include_guest_events); > > + return 0; > > +} > > + > > +static void mediated_pmu_unaccount_event(struct perf_event *event) > > +{ > > + if (!is_include_guest_event(event)) > > + return; > > + > > + atomic_dec(&nr_include_guest_events); > > +} > > > +int perf_create_mediated_pmu(void) > > +{ > > + guard(mutex)(&perf_mediated_pmu_mutex); > > + if (atomic_inc_not_zero(&nr_mediated_pmu_vms)) > > + return 0; > > + > > + if (atomic_read(&nr_include_guest_events)) > > + return -EBUSY; > > + > > + atomic_inc(&nr_mediated_pmu_vms); > > + return 0; > > +} > > +EXPORT_SYMBOL_GPL(perf_create_mediated_pmu); > > + > > +void perf_release_mediated_pmu(void) > > +{ > > + if (WARN_ON_ONCE(!atomic_read(&nr_mediated_pmu_vms))) > > + return; > > + > > + atomic_dec(&nr_mediated_pmu_vms); > > +} > > +EXPORT_SYMBOL_GPL(perf_release_mediated_pmu); > > These two things are supposed to be symmetric, but are implemented > differently; what gives? > > That is, should not both have the general shape: > > if (atomic_inc_not_zero(&A)) > return 0; > > guard(mutex)(&lock); > > if (atomic_read(&B)) > return -EBUSY; > > atomic_inc(&A); > return 0; > > Similarly, I would imagine both release variants to have the underflow > warn on like: > > if (WARN_ON_ONCE(!atomic_read(&A))) > return; > > atomic_dec(&A); > > Hmm? IIUC, you're suggesting someting like this? If so, that makes perfect sense to me. diff --git a/kernel/events/core.c b/kernel/events/core.c index c6368c64b866..fa2e7b722283 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6356,7 +6356,8 @@ static int mediated_pmu_account_event(struct perf_event *event) static void mediated_pmu_unaccount_event(struct perf_event *event) { - if (!is_include_guest_event(event)) + if (!is_include_guest_event(event) || + WARN_ON_ONCE(!atomic_read(&nr_include_guest_events))) return; atomic_dec(&nr_include_guest_events); > Also, EXPORT_SYMBOL_FOR_KVM() ? Ya, for sure. I posted this against a branch without EXPORT_SYMBOL_FOR_KVM(), because there are also hard dependencies on the for-6.19 KVM pull requests, and I didn't want to wait to post until 6.19-rc1 because of the impending winter break. Though I also simply forgot about these exports :-( These could also use EXPORT_SYMBOL_FOR_KVM(): EXPORT_SYMBOL_FOR_MODULES(perf_load_guest_lvtpc, "kvm"); EXPORT_SYMBOL_FOR_MODULES(perf_put_guest_lvtpc, "kvm"); > I can make these edits when applying, if/when we get to applying. Let me > continue reading. > _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv