linux-kernel - Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race

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Message-ID: <20151007150128.GC4508@potion.brq.redhat.com>
Date:	Wed, 7 Oct 2015 17:01:29 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Steve Rutherford <srutherford@...gle.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: fix edge EOI and IOAPIC reconfig race

2015-10-07 11:29+0200, Paolo Bonzini:
> On 13/08/2015 15:46, Radim Krčmář wrote:
>> +	if (kvm_x86_ops->sync_pir_to_irr(vcpu))
>> +		kvm_make_request(KVM_REQ_EVENT, vcpu);
>> +
> 
> The call to sync_pir_to_irr belongs more in vcpu_scan_ioapic, I think.

Will do so in v2.

> More importantly, I think that KVM_REQ_EVENT is a latent bug for
> kvm_vcpu_ioctl_get_lapic as well, so the call to kvm_make_request should
> go in vmx_sync_pir_to_irr or in a new kvm_sync_pir_to_irr wrapper.

True, thanks.  I'll make the request in kvm_apic_update_irr (unless
you'd prefer to have it in new kvm_sync_pir_to_irr).

>> +			    (e->fields.trig_mode == IOAPIC_EDGE_TRIG &&
>> +			     kvm_apic_pending_eoi(vcpu, e->fields.vector)))
> 
> Should we test again here that kvm_irq_has_notifier(ioapic->kvm,
> KVM_IRQCHIP_IOAPIC, index), to avoid unnecessarily marking other
> edge-triggered interrupts?

Other edge-triggered interrupts are skipped by a previous condition:

  if (e->fields.trig_mode == IOAPIC_LEVEL_TRIG ||
      kvm_irq_has_notifier(ioapic->kvm, KVM_IRQCHIP_IOAPIC, index) ||
      index == RTC_GSI)
         [we're here]

I think it is ok to ignore level-triggered RTC, but we do want to
include edge-triggered.
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