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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 B516FC7618F for ; Fri, 26 Jul 2019 22:58:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7ECD721994 for ; Fri, 26 Jul 2019 22:58:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726871AbfGZW6s (ORCPT ); Fri, 26 Jul 2019 18:58:48 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:50646 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726360AbfGZW6s (ORCPT ); Fri, 26 Jul 2019 18:58:48 -0400 Received: from pd9ef1cb8.dip0.t-ipconnect.de ([217.239.28.184] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hr9Ad-00042J-5J; Sat, 27 Jul 2019 00:58:40 +0200 Date: Sat, 27 Jul 2019 00:58:38 +0200 (CEST) From: Thomas Gleixner To: Marc Zyngier cc: Julien Grall , "linux-rt-users@vger.kernel.org" , anna-maria@linutronix.de, "bigeasy@linutronix.de" , "kvmarm@lists.cs.columbia.edu" , Julien Thierry , James Morse , Suzuki K Poulose Subject: Re: KVM Arm64 and Linux-RT issues In-Reply-To: Message-ID: References: User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Wed, 24 Jul 2019, Marc Zyngier wrote: > On 23/07/2019 18:58, Julien Grall wrote: > It really feels like a change in hrtimer_cancel semantics. From what I > understand, this is used to avoid racing against the softirq, but boy it > breaks things. > > If this cannot be avoided, this means we can't cancel the background > timer (which is used to emulate the vcpu timer while it is blocked > waiting for an interrupt), then we must move this canceling to the point > where the vcpu is unblocked (instead of scheduled), which may have some > side effects -- I'll have a look. > > But that's not the only problem: We also have hrtimers used to emulate > timers while the vcpu is running, and these timers are canceled in > kvm_timer_vcpu_put(), which is also called from a preempt notifier. > Unfortunately, I don't have a reasonable solution for that (other than > putting this hrtimer_cancel in a workqueue and start chasing the > resulting races). The fix is simple. See below. We'll add that to the next RT release. That will take a while as I'm busy with posting RT stuff for upstream :) Thanks, tglx 8<------------ --- a/virt/kvm/arm/arch_timer.c +++ b/virt/kvm/arm/arch_timer.c @@ -80,7 +80,7 @@ static inline bool userspace_irqchip(str static void soft_timer_start(struct hrtimer *hrt, u64 ns) { hrtimer_start(hrt, ktime_add_ns(ktime_get(), ns), - HRTIMER_MODE_ABS); + HRTIMER_MODE_ABS_HARD); }