Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751910AbdLMJee (ORCPT ); Wed, 13 Dec 2017 04:34:34 -0500 Received: from mail-pf0-f196.google.com ([209.85.192.196]:36603 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750880AbdLMJe2 (ORCPT ); Wed, 13 Dec 2017 04:34:28 -0500 X-Google-Smtp-Source: ACJfBoubvvjZzRO3ypSJKWAQoKYVIvw95kKYF2odh8b1veBT3O60FiabO8jLX0+q56q+efqkAExwD8rYW6/ShEVu9PE= MIME-Version: 1.0 In-Reply-To: References: <1513148407-2611-1-git-send-email-hejianet@gmail.com> From: Christoffer Dall Date: Wed, 13 Dec 2017 10:34:27 +0100 Message-ID: Subject: Re: [PATCH] KVM: arm/arm64: don't set vtimer->cnt_ctl in kvm_arch_timer_handler To: Marc Zyngier Cc: Auger Eric , Jia He , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.cs.columbia.edu" , Jia He , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2837 Lines: 70 On Wed, Dec 13, 2017 at 10:27 AM, Marc Zyngier wrote: > On 13/12/17 09:08, Auger Eric wrote: >> Marc, >> On 13/12/17 09:56, Marc Zyngier wrote: >>> Hi Jia, >>> >>> On 13/12/17 07:00, Jia He wrote: >>>> In our Armv8a server (qualcomm Amberwing, non VHE), after applying >>>> Christoffer's timer optimizing patchset(Optimize arch timer register >>>> handling), the guest is hang during kernel booting. >>>> >>>> The error root cause might be as follows: >>>> 1. in kvm_arch_timer_handler, it reset vtimer->cnt_ctl with current >>>> cntv_ctl register value. And then it missed some cases to update timer's >>>> irq (irq.level) when kvm_timer_irq_can_fire() is false >>>> 2. It causes kvm_vcpu_check_block return 0 instead of -EINTR >>>> kvm_vcpu_check_block >>>> kvm_cpu_has_pending_timer >>>> kvm_timer_is_pending >>>> kvm_timer_should_fire >>>> 3. Thus, the kvm hyp code can not break the loop in kvm_vcpu_block (halt >>>> poll process) and the guest is hang forever >>>> >>>> Fixes: b103cc3f10c0 ("KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit") >>>> Signed-off-by: Jia He >>>> --- >>>> virt/kvm/arm/arch_timer.c | 1 - >>>> 1 file changed, 1 deletion(-) >>>> >>>> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c >>>> index f9555b1..bb86433 100644 >>>> --- a/virt/kvm/arm/arch_timer.c >>>> +++ b/virt/kvm/arm/arch_timer.c >>>> @@ -100,7 +100,6 @@ static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id) >>>> vtimer = vcpu_vtimer(vcpu); >>>> >>>> if (!vtimer->irq.level) { >>>> - vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl); >>>> if (kvm_timer_irq_can_fire(vtimer)) >>>> kvm_timer_update_irq(vcpu, true, vtimer); >>>> } >>>> >>> >>> Which patches are you looking at? The current code in mainline looks >>> like this: >>> >>> vtimer = vcpu_vtimer(vcpu); >>> >>> vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl); >>> if (kvm_timer_irq_can_fire(vtimer)) >>> kvm_timer_update_irq(vcpu, true, vtimer); >>> >>> I'd suggest you use mainline and report if this doesn't work >> the removal of if (!vtimer->irq.level) test happened in: >> [PATCH v7 3/8] KVM: arm/arm64: Don't cache the timer IRQ level >> >> which is not upstream. > Ah, my bad (I have that series in my working tree already...). > > I still think Jia's approach to this is not quite right. If you don't > update the status of the timer by reading the HW value, how can you > decide whether the timer can fire or not? > Exactly. We need to know the exact kernel source, symptoms, how to reproduce, and then trace what's going on. It may be needed to tweak kvm_timer_is_pending(), but I don't yet see a case where it breaks. Thanks, -Christoffer