RE: [RFC PATCH 3/6] vfio: Extend iommu-info to return MSIs automap state

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> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Tuesday, October 06, 2015 4:15 AM
> To: Bhushan Bharat-R65777 <Bharat.Bhushan@xxxxxxxxxxxxx>
> Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx;
> christoffer.dall@xxxxxxxxxx; eric.auger@xxxxxxxxxx; pranavkumar@xxxxxxxxxx;
> marc.zyngier@xxxxxxx; will.deacon@xxxxxxx
> Subject: Re: [RFC PATCH 3/6] vfio: Extend iommu-info to return MSIs
> automap state
> 
> On Mon, 2015-10-05 at 06:00 +0000, Bhushan Bharat wrote:
> > > -1138,6 +1156,8 @@
> > > > static long vfio_iommu_type1_ioctl(void *iommu_data,
> > > >  		}
> > > >  	} else if (cmd == VFIO_IOMMU_GET_INFO) {
> > > >  		struct vfio_iommu_type1_info info;
> > > > +		struct iommu_domain_msi_maps msi_maps;
> > > > +		int ret;
> > > >
> > > >  		minsz = offsetofend(struct vfio_iommu_type1_info,
> > > iova_pgsizes);
> > > >
> > > > @@ -1149,6 +1169,18 @@ static long vfio_iommu_type1_ioctl(void
> > > > *iommu_data,
> > > >
> > > >  		info.flags = 0;
> > > >
> > > > +		ret = vfio_domains_get_msi_maps(iommu, &msi_maps);
> > > > +		if (ret)
> > > > +			return ret;
> > >
> > > And now ioctl(VFIO_IOMMU_GET_INFO) no longer works for any
> IOMMU
> > > implementing domain_get_attr but not supporting
> > > DOMAIN_ATTR_MSI_MAPPING.
> >
> > With this current patch version this will get the default assumed behavior
> as you commented on previous patch.
> 
> How so?

You are right, the ioctl will return failure. But that should be ok, right?

> 
> +               msi_maps->automap = true;
> +               msi_maps->override_automap = false;
> +
> +               if (domain->ops->domain_get_attr)
> +                       ret = domain->ops->domain_get_attr(domain, attr,
> + data);
> 
> If domain_get_attr is implemented, but DOMAIN_ATTR_MSI_MAPPING is
> not, ret should be an error code.

Currently it returns same error code returned by domain->ops->domain_get_attr(). 
I do not think we want to complicate that we return an error to user-space that msi's probably cannot be used but user-space can continue with Legacy interrupt, or you want that?

Thanks
-Bharat

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