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Subject: Re: [PATCH 1/3] KVM: s390: clear kicked_mask before sleeping again
To:     Halil Pasic <pasic@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Michael Mueller <mimu@linux.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Matthew Rosato <mjrosato@linux.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Pierre Morel <pmorel@linux.ibm.com>,
        Tony Krowiak <akrowiak@linux.ibm.com>,
        Niklas Schnelle <schnelle@linux.ibm.com>, farman@linux.ibm.com,
        kvm@vger.kernel.org
References: <20211019175401.3757927-1-pasic@linux.ibm.com>
 <20211019175401.3757927-2-pasic@linux.ibm.com>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
Message-ID: <6f57d209-ac92-2470-50f9-e790a45979e1@de.ibm.com>
Date:   Tue, 19 Oct 2021 23:22:49 +0200
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Am 19.10.21 um 19:53 schrieb Halil Pasic:
> The idea behind kicked mask is that we should not re-kick a vcpu that
> is already in the "kick" process, i.e. that was kicked and is
> is about to be dispatched if certain conditions are met.
> 
> The problem with the current implementation is, that it assumes the
> kicked vcpu is going to enter SIE shortly. But under certain
> circumstances, the vcpu we just kicked will be deemed non-runnable and
> will remain in wait state. This can happen, if the interrupt(s) this
> vcpu got kicked to deal with got already cleared (because the interrupts
> got delivered to another vcpu). In this case kvm_arch_vcpu_runnable()
> would return false, and the vcpu would remain in kvm_vcpu_block(),
> but this time with its kicked_mask bit set. So next time around we
> wouldn't kick the vcpu form __airqs_kick_single_vcpu(), but would assume
> that we just kicked it.
> 
> Let us make sure the kicked_mask is cleared before we give up on
> re-dispatching the vcpu.
> 
> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Fixes: 9f30f6216378 ("KVM: s390: add gib_alert_irq_handler()")

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>

> ---
>   arch/s390/kvm/kvm-s390.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 6a6dd5e1daf6..1c97493d21e1 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -3363,6 +3363,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>   
>   int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>   {
> +	clear_bit(vcpu->vcpu_idx, vcpu->kvm->arch.gisa_int.kicked_mask);
>   	return kvm_s390_vcpu_has_irq(vcpu, 0);
>   }
>   
>