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

[Wu, Feng]

> -----Original Message-----
> From: Yang Zhang [mailto:yang.zhang.wz@xxxxxxxxx]
> Sent: Thursday, January 21, 2016 11:06 AM
> To: Wu, Feng <feng.wu@xxxxxxxxx>; pbonzini@xxxxxxxxxx;
> rkrcmar@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the
> interrupt is not single-destination
> 
> On 2016/1/20 9:42, Feng Wu wrote:
> > 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@xxxxxxxxx>
> > ---
> >   arch/x86/kvm/vmx.c | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index e2951b6..13d14d4 100644
> > --- 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,
> >   		 */
> >
> >   		kvm_set_msi_irq(e, &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));
> > +			ret = irq_set_vcpu_affinity(host_irq, NULL);
> > +			pi_clear_sn(vcpu_to_pi_desc(vcpu));
> > +
> >   			continue;
> > +		}
> >
> >   		vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
> >   		vcpu_info.vector = irq.vector;
> >
> 
> I am still feel weird with this change: according the semantic of VT-d
> posted interrupt, the interrupt will injected to guest through posted
> notification and /proc/interrupts shows the same meaning. But now,
> without being aware of user, the interrupt changes to legacy way and it
> appears on different entry on /proc/interrupts. It looks weird.

I don't think it has problem here, IMO, this is exactly how it works.
There should be different entry for the interrupts in VT-d PI mode
and leagcy mode.

For VT-d PI mode, it is delivered by notification event, for legacy mode,
it is delivered by VFIO.

Thanks,
Feng

> 
> Any comments? Paolo.
> 
> --
> best regards
> yang