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

[Yang Zhang]

On 2016/1/21 11:14, Wu, Feng wrote:
> > -----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.

I am not saying any problem here. Just feel weird. From a normal user's 
point, he has turned on the VT-d pi and according the semantic of VT-d 
pi, he should not observe the interrupt through legacy mode, but now he 
do see it. Maybe print out a message here will be helpful, like what you 
did for disabled lapic found during irq injection.

> 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


--
best regards
yang