From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932133AbdA3TG7 (ORCPT ); Mon, 30 Jan 2017 14:06:59 -0500 Received: from mail-lf0-f42.google.com ([209.85.215.42]:34000 "EHLO mail-lf0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751023AbdA3TG4 (ORCPT ); Mon, 30 Jan 2017 14:06:56 -0500 Date: Mon, 30 Jan 2017 20:06:54 +0100 From: Christoffer Dall To: Marc Zyngier Cc: Jintack Lim , pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will.deacon@arm.com, andre.przywara@arm.com, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org Subject: Re: [RFC v2 06/10] KVM: arm/arm64: Update the physical timer interrupt level Message-ID: <20170130190654.GG16459@cbox> References: <1485479100-4966-1-git-send-email-jintack@cs.columbia.edu> <1485479100-4966-7-git-send-email-jintack@cs.columbia.edu> <86sho199jx.fsf@arm.com> <20170130150203.GD16459@cbox> <20170130184131.GE16459@cbox> <13152c8e-2256-4224-e15c-73c8d6ce06e4@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <13152c8e-2256-4224-e15c-73c8d6ce06e4@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 30, 2017 at 06:48:02PM +0000, Marc Zyngier wrote: > On 30/01/17 18:41, Christoffer Dall wrote: > > On Mon, Jan 30, 2017 at 05:50:03PM +0000, Marc Zyngier wrote: > >> On 30/01/17 15:02, Christoffer Dall wrote: > >>> On Sun, Jan 29, 2017 at 03:21:06PM +0000, Marc Zyngier wrote: > >>>> On Fri, Jan 27 2017 at 01:04:56 AM, Jintack Lim wrote: > >>>>> Now that we maintain the EL1 physical timer register states of VMs, > >>>>> update the physical timer interrupt level along with the virtual one. > >>>>> > >>>>> Note that the emulated EL1 physical timer is not mapped to any hardware > >>>>> timer, so we call a proper vgic function. > >>>>> > >>>>> Signed-off-by: Jintack Lim > >>>>> --- > >>>>> virt/kvm/arm/arch_timer.c | 20 ++++++++++++++++++++ > >>>>> 1 file changed, 20 insertions(+) > >>>>> > >>>>> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c > >>>>> index 0f6e935..3b6bd50 100644 > >>>>> --- a/virt/kvm/arm/arch_timer.c > >>>>> +++ b/virt/kvm/arm/arch_timer.c > >>>>> @@ -180,6 +180,21 @@ static void kvm_timer_update_mapped_irq(struct kvm_vcpu *vcpu, bool new_level, > >>>>> WARN_ON(ret); > >>>>> } > >>>>> > >>>>> +static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level, > >>>>> + struct arch_timer_context *timer) > >>>>> +{ > >>>>> + int ret; > >>>>> + > >>>>> + BUG_ON(!vgic_initialized(vcpu->kvm)); > >>>> > >>>> Although I've added my fair share of BUG_ON() in the code base, I've > >>>> since reconsidered my position. If we get in a situation where the vgic > >>>> is not initialized, maybe it would be better to just WARN_ON and return > >>>> early rather than killing the whole box. Thoughts? > >>>> > >>> > >>> The distinction to me is whether this will cause fatal crashes or > >>> exploits down the road if we're working on uninitialized data. If all > >>> that can happen if the vgic is not initialized, is that the guest > >>> doesn't see interrupts, for example, then a WARN_ON is appropriate. > >>> > >>> Which is the case here? > >>> > >>> That being said, do we need this at all? This is in the critial path > >>> and is actually measurable (I know this from my work on the other timer > >>> series), so it's better to get rid of it if we can. Can we simply > >>> convince ourselves this will never happen, and is the code ever likely > >>> to change so that it gets called with the vgic disabled later? > >> > >> That'd be the best course of action. I remember us reworking some of > >> that in the now defunct vgic-less series. Maybe we could salvage that > >> code, if only for the time we spent on it... > >> > > Ah, we never merged it? Were we waiting on a userspace implementation > > or agreement on the ABI? > > We were waiting on the userspace side to be respun against the latest > API, and there were some comments from Peter (IIRC) about supporting > PPIs in general (the other timers and the PMU, for example). > > None of that happened, as the most vocal proponent of the series > apparently lost interest. > > > There was definitely a useful cleanup with the whole enabled flag thing > > on the timer I remember. > > Indeed. We should at least try to resurrect that bit. > It's probably worth it trying to resurrect the whole thing I think, especially since I think the implementation ended up looking quite nice. I can add a rebase of that to my list of never-ending timer rework. Thanks, -Christoffer