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=-1.0 required=3.0 tests=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 496BAC433FF for ; Sat, 27 Jul 2019 11:13:46 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id E4BF52077C for ; Sat, 27 Jul 2019 11:13:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E4BF52077C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 297354A549; Sat, 27 Jul 2019 07:13:45 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 1yeJ8ULhjcrW; Sat, 27 Jul 2019 07:13:44 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 1E3844A54D; Sat, 27 Jul 2019 07:13:44 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id F18714A549 for ; Sat, 27 Jul 2019 07:13:42 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id BocTynQxDtHj for ; Sat, 27 Jul 2019 07:13:41 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id E1CED4A51D for ; Sat, 27 Jul 2019 07:13:41 -0400 (EDT) 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 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") Cc: "linux-rt-users@vger.kernel.org" , "bigeasy@linutronix.de" , Julien Grall , anna-maria@linutronix.de, "kvmarm@lists.cs.columbia.edu" X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm