linux-kernel - Re: [RFC v2 06/10] KVM: arm/arm64: Update the physical timer interrupt level

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Date:   Wed, 1 Feb 2017 09:04:40 +0100
From:   Christoffer Dall <christoffer.dall@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Jintack Lim <jintack@...columbia.edu>, pbonzini@...hat.com,
        rkrcmar@...hat.com, linux@...linux.org.uk, catalin.marinas@....com,
        will.deacon@....com, andre.przywara@....com, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 06/10] KVM: arm/arm64: Update the physical timer
 interrupt level

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 <jintack@...columbia.edu> 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 <jintack@...columbia.edu>
> > ---
> >  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?
> 

Could we help this series along by saying that since this BUG_ON already
exists in the kvm_timer_update_mapped_irq function, then it just
preserves functionality and it's up to someone else (me) to remove the
BUG_ON from both functions later in life?

Thanks,
-Christoffer