linux-kernel - Re: [PATCH] generic: Add the exception case checking routine for ppi interrupt

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Date:   Tue, 30 Aug 2016 12:21:13 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     "majun (F)" <majun258@...wei.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        dingtianhong@...wei.com, guohanjun@...wei.com
Subject: Re: [PATCH] generic: Add the exception case checking routine for ppi
 interrupt

On Tue, Aug 30, 2016 at 12:07:36PM +0100, Marc Zyngier wrote:
> +Mark
> On 30/08/16 11:35, majun (F) wrote:
> > 在 2016/8/30 16:50, Marc Zyngier 写道:
> >> On 30/08/16 05:17, MaJun wrote:
> >>> From: Ma Jun <majun258@...wei.com>
> >>>
> >>> During system booting, if the interrupt which has no action registered
> >>> is triggered, it would cause system panic when try to access the
> >>> action member.
> >>
> >> And why would that interrupt be enabled? If you enable a PPI before
> >> registering a handler, you're doing something wrong.
> > 
> > Actually,the problem described above happened during the capture
> > kernel booting.
> > 
> > In my system, sometimes there is a pending physical timer
> > interrupt(30) when the first kernel panic and the status is kept
> > until the capture kernel booting.
> 
> And that's perfectly fine. The interrupt can be pending forever, as it
> shouldn't get enabled.
> 
> > So, this interrupt will be handled during capture kernel booting.
> 
> Why? Who enables it?
> 
> > Becasue we use virt timer interrupt but not physical timer interrupt
> > in capture kernel, the interrupt 30 has no action handler.
> 
> Again: who enables this interrupt? Whichever driver enables it should be
> fixed.

I'm also at a loss.

In this case, arch_timer_uses_ppi must be VIRT_PPI. So in
arch_timer_register(), we'll only request_percpu_irq the virt PPI.
arch_timer_has_nonsecure_ppi() will be false, given arch_timer_uses_ppi
is VIRT_PPI, so in arch_timer_starting_cpu() we'll only
enable_percpu_irq() the virt PPI.

We don't fiddle with arch_timer_uses_ppi after calling
arch_timer_register(). So I can't see how we could enable another IRQ in
this case.

Looking at the driver in virt/kvm/arm/arch_timer.c, we only enable what
we've succesfully requested, so it doesnt' seem like there's an issue
there.

>From a quick look at teh GIC driver, it looks like we reset PPIs
correctly, so it doesn't look like we have a "latent enable".

Thanks,
Mark.