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Date: Tue, 26 Nov 2013 18:29:17 +0200
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Subject: Re: [Qemu-devel] [RFC] create a single workqueue for each vm to
 update vm irq routing table
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To: Paolo Bonzini <pbonzini@redhat.com>, Gleb Natapov <gleb@redhat.com>
Cc: "Huangweidong (C)" <weidong.huang@huawei.com>, KVM <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>, "Zhanghaoyu (A)" <haoyu.zhang@huawei.com>, Luonengjun <luonengjun@huawei.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Zanghongyong <zanghongyong@huawei.com>, Avi Kivity <avi.kivity@gmail.com>, "Jinxin (F)" <jinxin712@huawei.com>

On 11/26/2013 06:28 PM, Paolo Bonzini wrote:
> Il 26/11/2013 17:24, Gleb Natapov ha scritto:
>>>      VCPU writes to routing table
>>>                                         e = entry from IRQ routing table
>>>      kvm_irq_routing_update(kvm, new);
>>>      VCPU resumes execution
>>>                                         kvm_set_msi_irq(e, &irq);
>>>                                         kvm_irq_delivery_to_apic_fast();
>>>
>>> where the entry is stale but the VCPU has already resumed execution.
>> So how is it different from what we have now:
>>
>> disable_irq()
>> VCPU writes to routing table
>>                                   e = entry from IRQ routing table
>>                                   kvm_set_msi_irq(e, &irq);
>>                                   kvm_irq_delivery_to_apic_fast();
>> kvm_irq_routing_update(kvm, new);
>> synchronize_rcu()
>> VCPU resumes execution
>> enable_irq()
>> receive stale irq
> Adding a "disable/enable IRQs" looks like a relatively big change.  But
> perhaps it's not for some reason I'm missing.
>

Those are guest operations, which may not be there at all.