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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FFA4C636CA for ; Wed, 21 Jul 2021 08:57:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 62D45610D2 for ; Wed, 21 Jul 2021 08:57:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237406AbhGUIN6 (ORCPT ); Wed, 21 Jul 2021 04:13:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:50736 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237228AbhGUIAa (ORCPT ); Wed, 21 Jul 2021 04:00:30 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 743FA60D07; Wed, 21 Jul 2021 08:40:48 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1m67mY-00Ef7k-Ll; Wed, 21 Jul 2021 09:40:46 +0100 Date: Wed, 21 Jul 2021 09:40:46 +0100 Message-ID: <87h7go2h69.wl-maz@kernel.org> From: Marc Zyngier To: Joel Fernandes Cc: Sergey Senozhatsky , Will Deacon , Suleiman Souhlal , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support In-Reply-To: References: <20210709043713.887098-1-senozhatsky@chromium.org> <20210709043713.887098-5-senozhatsky@chromium.org> <874kcz33g5.wl-maz@kernel.org> 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/27.1 (x86_64-pc-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: joelaf@google.com, senozhatsky@chromium.org, will@kernel.org, suleiman@google.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 Jul 2021 19:44:53 +0100, Joel Fernandes wrote: > > On Mon, Jul 12, 2021 at 12:24 PM Marc Zyngier wrote: > > > [...] > > > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > > > { > > > + kvm_update_vcpu_preempted(vcpu, true); > > > > This doesn't look right. With this, you are now telling the guest that > > a vcpu that is blocked on WFI is preempted. This really isn't the > > case, as it has voluntarily entered a low-power mode while waiting for > > an interrupt. Indeed, the vcpu isn't running. A physical CPU wouldn't > > be running either. > > Can that be cured by just checking vcpu->preempted before calling > kvm_update_vcpu_preempted() ? It isn't obvious to me that this is the right thing to do. vcpu->preempted is always updated on sched-out from the preempt notifier if the vcpu was on the run-queue, so my guess is that it will always be set when switching to another task. What you probably want is to check whether the vcpu is blocked by introspecting the wait-queue with: scuwait_active(kvm_arch_vcpu_get_wait(vcpu) which will tell you whether you are blocking or not. We are already using a similar construct for arming a background timer in this case. M. -- Without deviation from the norm, progress is not possible.