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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DC916C433EF for ; Fri, 17 Dec 2021 15:54:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235191AbhLQPy2 (ORCPT ); Fri, 17 Dec 2021 10:54:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235223AbhLQPy0 (ORCPT ); Fri, 17 Dec 2021 10:54:26 -0500 Received: from mail-wr1-x432.google.com (mail-wr1-x432.google.com [IPv6:2a00:1450:4864:20::432]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A6B26C061574; Fri, 17 Dec 2021 07:54:25 -0800 (PST) Received: by mail-wr1-x432.google.com with SMTP id o13so4847134wrs.12; Fri, 17 Dec 2021 07:54:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=AHfUikZmyD4dINCWakIQJtobxvYGz5CvtkfmXC/JM0U=; b=kkoc4FHM+YuQr9vZVtoceLdb6WDPQLhgj4yrAneG0S9X+rspnO/cHTjzzLHoFMucxW f/hpbjjYx/5FXX57Y9KVVq6kXDhnnu1UaInliIeJ1fVNCwxAG7x1ch6jrIUGx3e4q4vb i4ozNkufUfpUMXtDhBwJxFdBi5dYXn3N6+rAKS49Kca2spsxiL1X5jXW5OxxQExxyPB5 mtn8C7cwExGjebtfAkAs6vAWhPNDr6SD3aHoHqaB73+jKuH7VQjS2Rp4CFL3Cqyr7pTJ p8dmjR4mYm6fdo4+GoSjpl6nYl4XwkcOKU0xajZXIL2YxeDPiL3khk6uQ3bl7z+Kg35W HKGQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:message-id:date:mime-version:user-agent :subject:content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=AHfUikZmyD4dINCWakIQJtobxvYGz5CvtkfmXC/JM0U=; b=ULL3w/O3QGgSQ0xr5HBhJYm4PjfFL60bxQoxavULTaTn3XRp5cQTTQdhQ3/gGIHK2p iD3mJA2vnsZrNfMdt3BEq4h/w99kW8JNbhn3hajYwEChtv96vl79Y6fsVPKfAmVomYvN 0arzn/td1zk0PFoCVvb/x+XdLqsAlxdJGCl/bi3j5vNY4CicFgTdDs5u5Zq9MTnR8hN3 9vGLaRHbRDMTXGGaVqTmI/Ht7g4Ws4a4keZcFIMCz5fIADb1Jmj2ZGcSE1usokZNtoLP Ux2cl33cpQR8cj1ycCsq5uRegqJEpPSa96Nl036yVVqzpi8pzB/9SxUnUVyhpnu28cq3 DLag== X-Gm-Message-State: AOAM530HSxGI4ESVpZwC3rSk23zit9McxI4wZwBobCplU5PGYqQXVPwm XIgX6OtgUnpuLCmr5WCLxGY= X-Google-Smtp-Source: ABdhPJyGxYhZSxDUxszzp9INdkaMS8zLvwT/pmwuIPWM1rk+PG085n9I8oYQLKBFYA2zw6Fgd+MA6A== X-Received: by 2002:a5d:6d8b:: with SMTP id l11mr3077055wrs.25.1639756464297; Fri, 17 Dec 2021 07:54:24 -0800 (PST) Received: from ?IPV6:2001:b07:6468:f312:48f9:bea:a04c:3dfe? ([2001:b07:6468:f312:48f9:bea:a04c:3dfe]) by smtp.googlemail.com with ESMTPSA id k13sm7619520wri.6.2021.12.17.07.54.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Dec 2021 07:54:23 -0800 (PST) Sender: Paolo Bonzini Message-ID: <9ab8107f-ff41-6a9e-57e1-a261bea93aca@redhat.com> Date: Fri, 17 Dec 2021 16:54:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: Possible nohz-full/RCU issue in arm64 KVM Content-Language: en-US To: Mark Rutland , Nicolas Saenz Julienne Cc: paulmck , maz , frederic , linux-kernel , rcu , Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel References: <70f112072d9496d21901946ea82832d3ed3a8cb2.camel@redhat.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/17/21 15:38, Mark Rutland wrote: > For example kvm_guest_enter_irqoff() calls guest_enter_irq_off() which calls > vtime_account_guest_enter(), but kvm_guest_exit_irqoff() doesn't call > guest_exit_irq_off() and the call to vtime_account_guest_exit() is open-coded > elsewhere. Also, guest_enter_irq_off() conditionally calls > rcu_virt_note_context_switch(), but I can't immediately spot anything on the > exit side that corresponded with that, which looks suspicious. rcu_note_context_switch() is a point-in-time notification; it's not strictly necessary, but it may improve performance a bit by avoiding unnecessary IPIs from the RCU subsystem. There's no benefit from doing it when you're back from the guest, because at that point the CPU is just running normal kernel code. Paolo