linux-kernel - Re: [PATCH] KVM: arm/arm64: don't set vtimer->cnt_ctl in kvm_arch_timer

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Date:   Wed, 13 Dec 2017 10:20:20 +0100
From:   Christoffer Dall <christoffer.dall@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Jia He <hejianet@...il.com>, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        Jia He <jia.he@...-semitech.com>
Subject: Re: [PATCH] KVM: arm/arm64: don't set vtimer->cnt_ctl in
 kvm_arch_timer_handler

On Wed, Dec 13, 2017 at 08:56:12AM +0000, 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 <jia.he@...-semitech.com>
> > ---
> >  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.
> 

That looks like you have the level-triggered mapped series applied?

That would be an interesting data point to get from Jia as well though.
Jia, can you try applying this series and see if it helps?

git://git.kernel.org/pub/scm/linux/kernel/git/cdall/linux.git level-mapped-v7

Thanks,
-Christoffer
> Thanks,
> 
> 	M.
> -- 
> Jazz is not dead. It just smells funny...