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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 EF801C7618B for ; Sat, 27 Jul 2019 11:13:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D51162077C for ; Sat, 27 Jul 2019 11:13:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564226022; bh=LWavvunfZ6DOPAvWg/hPgbTfI65IQ1C/RnxwQAZfUus=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=AimhimyJrGCz0yfGQkUF+0zEGvVo6MqyJzF0PGm8jiMOD2AMfcFcUZRGNCDHudpVh TqZX5ZYX1vEZHtIdZUK45FBVtCKeazBlZFjnjvfI6b7xHTHtRnrQ4V0JcG9WYwfjXr r3Rnnv3/x2pD6P5fiGayTue0vwEg6wm58C9Yp82w= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728816AbfG0LNm (ORCPT ); Sat, 27 Jul 2019 07:13:42 -0400 Received: from foss.arm.com ([217.140.110.172]:52514 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725875AbfG0LNm (ORCPT ); Sat, 27 Jul 2019 07:13:42 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5EDCB28; Sat, 27 Jul 2019 04:13:41 -0700 (PDT) Received: from big-swifty.misterjones.org (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C7D5E3F694; Sat, 27 Jul 2019 04:13:39 -0700 (PDT) Date: Sat, 27 Jul 2019 12:13:38 +0100 Message-ID: <86zhkzn319.wl-maz@kernel.org> From: Marc Zyngier To: Thomas Gleixner Cc: Julien Grall , "linux-rt-users@vger.kernel.org" , , "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: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 EasyPG/1.0.0 Emacs/26 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Organization: Approximate MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org Hi Thomas, On Fri, 26 Jul 2019 23:58:38 +0100, Thomas Gleixner wrote: > > 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 :) Ah, thanks for that! And yes, looking forward to RT upstream, it's just about time! ;-) > > 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); > } > That's pretty neat, and matches the patch you already have for x86. Feel free to add my Acked-by: Marc Zyngier Thanks, M. -- Jazz is not dead, it just smells funny.