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 01:49:31 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Radim Krcmár <rkrcmar@...hat.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>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the
 interrupt is not single-destination



> -----Original Message-----
> From: Radim Krčmář [mailto:rkrcmar@...hat.com]
> Sent: Friday, January 22, 2016 12:20 AM
> To: Wu, Feng <feng.wu@...el.com>
> Cc: pbonzini@...hat.com; linux-kernel@...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
> 
> 2016-01-20 09:42+0800, Feng Wu:
> > When the interrupt is not single destination any more, we need
> > to change back IRTE to remapped mode explicitly.
> >
> > Signed-off-by: Feng Wu <feng.wu@...el.com>
> > ---
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > @@ -10764,8 +10764,17 @@ static int vmx_update_pi_irte(struct kvm
> *kvm, unsigned int host_irq,
> > -		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?

Thanks,
Feng

Thanks,
Feng

> 
> Thanks.
> 
> > +			ret = irq_set_vcpu_affinity(host_irq, NULL);
> > +			pi_clear_sn(vcpu_to_pi_desc(vcpu));
> > +
> >  			continue;
> > +		}