linux-kernel - [PATCH 1/3] KVM: s390: clear kicked

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Date:   Tue, 19 Oct 2021 19:53:59 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Michael Mueller <mimu@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Halil Pasic <pasic@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.ibm.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>, farman@...ux.ibm.com,
        kvm@...r.kernel.org
Subject: [PATCH 1/3] KVM: s390: clear kicked_mask before sleeping again

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@...ux.ibm.com>
Reported-by: Matthew Rosato <mjrosato@...ux.ibm.com>
Fixes: 9f30f6216378 ("KVM: s390: add gib_alert_irq_handler()")
---
 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);
 }

-- 
2.25.1