linux-kernel - Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the interrupt is not single-destination

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Date:	Fri, 22 Jan 2016 14:05:51 +0100
From:	Radim Krcmár <rkrcmar@...hat.com>
To:	"Wu, Feng" <feng.wu@...el.com>
Cc:	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the
 interrupt is not single-destination

2016-01-22 01:49+0000, Wu, Feng:
>> From: Radim Krčmář [mailto:rkrcmar@...hat.com]
>> 2016-01-20 09:42+0800, Feng Wu:
>> > -		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu))
>> > +		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
>> > +			/*
>> > +			 * Make sure the IRTE is in remapped mode if
>> > +			 * we don't handle it in posted mode.
>> > +			 */
>> > +			pi_set_sn(vcpu_to_pi_desc(vcpu));
>> 
>> What could go wrong if we didn't suppress notifications here?
> 
> This is a good question. I also thought about this before, but after
> thinking it a bit more, seems we don't need to do this. 
> If we don't do this, the in-flight interrupts will continue to be
> delivered in PI mode while we are changing it to remapped
> mode in IRTE. Even if we do this, the in-flight interrupts are
> also delivered in PI mode before setting 'SN' anyway, so seems
> we really don't need this, what is your opinion?

I'd remove it.