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 48B2CEA7190 for ; Sun, 19 Apr 2026 14:35:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: References:In-Reply-To:Subject:Cc:To:From:Message-ID:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ad3sYeJiUdtOBrUM0YRkCrJpayckna3u2zMOf3EIdMA=; b=PjQAVd0CvLO91kANWAJzrstc/q yuL7TGYGQodwIg9P7gtc8WSbPXoAZb/6Mrt/unRkZTJXledaBsY+8h24ftKXyKMCRi3/rsCwt3LZP 5XZz30fBXABORzPdJVcMUFyUrLyBbJlb65UVgwoVmSiiz4RDJD5Jsk3OhWBAY6xQuurKGWEzPKs6b JPQ/rTM7qKKwoJ8OYEO+2inQm5ayR3TfXApdsNqJJ4fAhNrnKymAXVeL2ewZr5HJ8fIurCzi0nbr4 dsK6bJ1JJ9P3QGRhiVRLzlww2U3l6E4NE2GH3mWl+U+5Jd7Q3cETOE7YmNG8MmzS8hcPCwB5EKpIb nfiTNDsQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wETEg-00000005r0r-2qZj; Sun, 19 Apr 2026 14:34:58 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wETEf-00000005r0l-1oLp for linux-arm-kernel@lists.infradead.org; Sun, 19 Apr 2026 14:34:57 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 2526460103; Sun, 19 Apr 2026 14:34:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C6572C2BCAF; Sun, 19 Apr 2026 14:34:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776609295; bh=OPx8O9OYxVipA24HAer+gnhYq6XtrF4PKMKTsL1iRy0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=aLd5NYX01/n8EbtB7Djb5saIze5EfciDiFDuH/LEdD6cwKVZmN1vFFCV2HNdgzomp KtQWGmVSJpSHpBEnHpr1Q2QZCkk5OYMYueK5IlZJN6fUxQ7QS0lgOVKo7t5y0aryjJ 4XftYT8LHyK6vJhmHelm2hns2vFlgAPcu+z0kRFhK2pt/A3NHyCD6B4P79T5p4tY30 G4RTIrb0Bm2N/kOBY9gJC2wbz9uIgMmnTUIJ2s4dFIisoHhCvb3rQSUSxXIkUlrU0o 517Rm6iChYR1OEuD+oKPtS1BSJoXRRqdV7fMp3p314hI1TegwoxbiI0TEw8sahJToe LhER4l3ELHIcQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=lobster-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wETEb-0000000CqLm-1aIO; Sun, 19 Apr 2026 14:34:53 +0000 Date: Sun, 19 Apr 2026 15:34:52 +0100 Message-ID: <87mryzauib.wl-maz@kernel.org> From: Marc Zyngier To: Akihiko Odaki Cc: Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Kees Cook , "Gustavo A. R. Silva" , Paolo Bonzini , Jonathan Corbet , Shuah Khan , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, devel@daynix.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v7 2/4] KVM: arm64: PMU: Protect the list of PMUs with RCU In-Reply-To: <20260418-hybrid-v7-2-2bf39ad009bf@rsg.ci.i.u-tokyo.ac.jp> References: <20260418-hybrid-v7-0-2bf39ad009bf@rsg.ci.i.u-tokyo.ac.jp> <20260418-hybrid-v7-2-2bf39ad009bf@rsg.ci.i.u-tokyo.ac.jp> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: odaki@rsg.ci.i.u-tokyo.ac.jp, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, kees@kernel.org, gustavoars@kernel.org, pbonzini@redhat.com, corbet@lwn.net, shuah@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, devel@daynix.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, 18 Apr 2026 09:14:24 +0100, Akihiko Odaki wrote: > > Convert the list of PMUs to a RCU-protected list that has primitives to > avoid read-side contention. > > Signed-off-by: Akihiko Odaki > --- > arch/arm64/kvm/pmu-emul.c | 14 ++++++-------- > 1 file changed, 6 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c > index 59ec96e09321..ef5140bbfe28 100644 > --- a/arch/arm64/kvm/pmu-emul.c > +++ b/arch/arm64/kvm/pmu-emul.c > @@ -7,9 +7,9 @@ > #include > #include > #include > -#include > #include > #include > +#include > #include > #include > #include > @@ -26,7 +26,6 @@ static bool kvm_pmu_counter_is_enabled(struct kvm_pmc *pmc); > > bool kvm_supports_guest_pmuv3(void) > { > - guard(mutex)(&arm_pmus_lock); > return !list_empty(&arm_pmus); Please read include/linux/rculist.h and the discussion about the interaction of list_empty() with RCU-protected lists. How about using list_first_or_null_rcu() for peace of mind? Thanks, M. -- Jazz isn't dead. It just smells funny.