> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, July 17, 2012 10:08 PM
> To: Bhushan Bharat-R65777
> Cc: Wood Scott-B07421; Alexander Graf; kvm-ppc@xxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx; bharatb.yadav@xxxxxxxxx; Benjamin Herrenschmidt; Kumar Gala
> Subject: Re: [PATCH 2/2 v2] KVM: PPC: booke: Add watchdog emulation
>
> On 07/17/2012 06:31 AM, Bhushan Bharat-R65777 wrote:
> >>>> int kvm_arch_vcpu_runnable(struct kvm_vcpu *v) {
> >>>> - return !(v->arch.shared->msr & MSR_WE) ||
> >>>> - !!(v->arch.pending_exceptions) ||
> >>>> - v->requests;
> >>>> + bool ret = !(v->arch.shared->msr & MSR_WE) ||
> >>>> + !!(v->arch.pending_exceptions) ||
> >>>> + v->requests;
> >>>> +
> >>>> + ret = ret || kvmppc_get_tsr_wrc(v);
> >>>
> >>> Why do you need to declare the cpu as non-runnable when a watchdog
> >>> event occured?
> >>
> >> It's the other way around -- it's always runnable when a watchdog
> >> exit is pending. It's like a pending exception.
> >
> > With the above check, Are we trying to handle the case where watchdog
> > interrupt bit in pending_exception is cleared by guest after final
> > expiry but before the qemu exit?
>
> No, we're just trying to test the actual condition we want to exit on.
> The watchdog interrupt might be masked (either with WIE or CE).
If the interrupt is masked then still the pending_exception will be set. But interrupt will not be delivered to guest and Final expiry can still cause reset etc !! Right?
>
> > And we want that if TSR.WRS update
> > wins the race with clearing of watchdog interrupt condition from guest
> > then anyways let QEMU exit with reason KVM_EXIT_WDT?
>
> What race? If ENW and WIS are both set when the watchdog timer fires, it's a
> final expiration. It's irrelevant what happens to WIS after that point, before
> enforcement kicks in.
What I was thinking of was if we can remove this check in vcpu_runnable() and use watchdog bit in pending_exception to qualify vcpu_runnable()
>
> > What if we do not allow guest clear watchdog interrupt condition if
> > final expiry already happened?
>
> What would that solve?
Removing " ret || kvmppc_get_tsr_wrc(v);" this from vcpu_runnable().
Thanks
-Bharat
>
> -Scott
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