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Date: Tue, 26 Nov 2013 17:28:23 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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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: Gleb Natapov <gleb@redhat.com>
Cc: Avi Kivity <avi@cloudius-systems.com>, "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>

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.

Paolo