From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH 1/3] KVM: Emulation MSI-X mask bits for assigned devices
Date: Thu, 30 Sep 2010 13:25:17 -0300
Message-ID: <20100930162517.GB29881@amt.cnet>
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 <201009290917.14843.sheng@linux.intel.com>
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Cc: "Michael S. Tsirkin" <mst@redhat.com>, Avi Kivity <avi@redhat.com>,
	kvm@vger.kernel.org
To: Sheng Yang <sheng@linux.intel.com>
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On Wed, Sep 29, 2010 at 09:17:14AM +0800, Sheng Yang wrote:
> > > +	else {
> > > +		enable_irq(irq);
> > > +		if (assigned_dev->guest_msix_entries[index].flags &
> > > +				KVM_ASSIGNED_MSIX_PENDING)
> > > +			schedule_work(&assigned_dev->interrupt_work);
> > > +	}
> > 
> > Hmm, won't this lose interrupts which were sent while bit was pending?
> > It is also pretty heavy if as you say guests touch the mask a lot.
> > I think we must keep the interrupt disabled, just set a bit
> > and delay interrupt injection until vector is unmasked
> > or deleted. The interface to do this will need more thought:
> > e.g. how can userspace clear this bit then?
> 
> I think it's fine. Because we didn't modify pending bit here, and the interrupt 
> handler would schedule an work to check it regardless of if the IRQ is disable. By 
> this meaning, no interrupt would be lose.

AFAICS unmasking the host irq will trigger pending message. If thats
correct, it should be fine.