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 6173AC433EF for ; Fri, 17 Dec 2021 16:51:59 +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:Reply-To: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:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=CEXWxqoo8gi30J5U3rSezq3n8x8yX8tRlNiHxEKxzH4=; b=157AlV6gKzAjN3 9rKviZSSXFVY6GMiMuI8Gv85aYBdppndCka61FDUalcBLX91IWyBrbG96PXPBDWutkf4F8ghVIIOe aUVkvaBjLMtJ5MoaktT6tJ53PTH8W4YNgCc7RwZbkWd54nreTylmSRsZW2tcAx1Tf3AIUlPg0l/ak faiQCBccEsDvI7/xbaRiNUDA+YIWbOE+1uAlBROFtzJQp3SuS3+DXT9q0H1j1c/uJVaURwaDCSZDT oRgUgA/zPFWSfmWM79SfhWS4MdGEJRJRpELti4ouLTs7ukO3H2yI9PfKxBmLXfSYyBi2fgo5GjTeN BEqQXD3dkJG+GUnvy6iA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1myGQk-00BGOW-Io; Fri, 17 Dec 2021 16:50:05 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1myFlv-00B4XP-Vo for linux-arm-kernel@lists.infradead.org; Fri, 17 Dec 2021 16:07:53 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B124E62287; Fri, 17 Dec 2021 16:07:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 21AF3C36AE7; Fri, 17 Dec 2021 16:07:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639757270; bh=CLb/vJNslUVn2r+sZTAnMRXCOXn59toIUCwh/IkwYQc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=CauBV+W9fQqYJLQzdeFA0ISzNJpiTCqIKyxongSwUvHWWkmV6ZD9Fz7RP0oQ0HBqY cMixjLYJ6SzKCdfisxaElhQrLY9OTob7qk2q5CMOldEHODGQRb++uLrqE0Bsij7oBd Sny8bv8CbPIc1qIylGoq0z+KgoMCXO916kbjwDU5VgipqhhmbDonLjrNwKYZE6mMiC lrSvid8A7axsjUwi7wLgvumi7Q6GMMEUZBFoGZlR79akUsGpEWTFlDlE/IhWSFfO7g A47nTjy8S6M8YD1L3F8xNYUTLIkoH/EtFPc5eoqGUzNIr1k3C/wOEm8glNIEVob0i2 U/5/faGEZFJqA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id D3C9F5C0610; Fri, 17 Dec 2021 08:07:49 -0800 (PST) Date: Fri, 17 Dec 2021 08:07:49 -0800 From: "Paul E. McKenney" To: Paolo Bonzini Cc: Mark Rutland , Nicolas Saenz Julienne , maz , frederic , linux-kernel , rcu , Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel Subject: Re: Possible nohz-full/RCU issue in arm64 KVM Message-ID: <20211217160749.GS641268@paulmck-ThinkPad-P17-Gen-1> References: <70f112072d9496d21901946ea82832d3ed3a8cb2.camel@redhat.com> <9ab8107f-ff41-6a9e-57e1-a261bea93aca@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <9ab8107f-ff41-6a9e-57e1-a261bea93aca@redhat.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211217_080752_135514_BAC4CD36 X-CRM114-Status: GOOD ( 16.86 ) 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: , Reply-To: paulmck@kernel.org 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 Fri, Dec 17, 2021 at 04:54:22PM +0100, Paolo Bonzini wrote: > 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. Do scheduling-clock interrupts from guest mode have the "user" parameter set? If so, that would keep RCU happy. Thanx, Paul _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel