RE: [PATCH v9 12/18] vfio: Register/unregister irq_bypass_producer

["Wu, Feng" <feng.wu@intel.com>]

> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@redhat.com]
> Sent: Wednesday, April 27, 2016 4:08 AM
> To: Wu, Feng <feng.wu@intel.com>
> Cc: pbonzini@redhat.com; joro@8bytes.org; mtosatti@redhat.com;
> eric.auger@linaro.org; kvm@vger.kernel.org; iommu@lists.linux-
> foundation.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v9 12/18] vfio: Register/unregister irq_bypass_producer
> 
> On Fri, 18 Sep 2015 22:29:50 +0800
> Feng Wu <feng.wu@intel.com> wrote:
> 
>  @@ -360,6 +361,14 @@ static int vfio_msi_set_vector_signal(struct
>  vfio_pci_device *vdev,
> >  		return ret;
> >  	}
> >
> > +	vdev->ctx[vector].producer.token = trigger;
> > +	vdev->ctx[vector].producer.irq = irq;
> > +	ret = irq_bypass_register_producer(&vdev->ctx[vector].producer);
> > +	if (unlikely(ret))
> > +		dev_info(&pdev->dev,
> > +		"irq bypass producer (token %p) registeration fails: %d\n",
> > +		vdev->ctx[vector].producer.token, ret);
> > +
> >  	vdev->ctx[vector].trigger = trigger;
> >
> >  	return 0;
> 
> Digging back into the IRQ producer/consumer thing, I'm not sure how we
> should be handling a failure here, but it turns out that what we have
> is pretty sub-optimal.  Any sort of testing on AMD hits this dev_info
> because kvm_arch_irq_bypass_add_producer() returns -EINVAL without
> kvm_x86_ops->update_pi_irte which is only implemented for vmx.  Clearly
> we don't want to spew confusing error messages for a feature that does
> not exist.
> 
> The easiest option is to simply make this error silent, but should
> registering a producer/consumer really fail due to a mismatch on the
> other end or should the __connect sequence fail silently, which both
> ends would know about (if they care) due to the add/del handshake
> between them?  Perhaps for now we simply need a stable suitable fix to
> silence the dev_info above, but longer term, registration shouldn't
> fail for mismatches like this.  Thoughts?  Thanks,

Can we just return 0 when kvm_x86_ops->update_pi_irte is NULL in
kvm_arch_irq_bypass_add_producer?

Thanks,
Feng

> 
> Alex