RE: [PATCH v2 04/11] iommufd: Pass parent hwpt and user_data to iommufd_hw_pagetable_alloc()

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Saturday, May 20, 2023 3:09 AM
> 
> On Fri, May 19, 2023 at 09:06:20AM +0000, Tian, Kevin wrote:
> 
> > > @@ -73,14 +77,22 @@ int iommufd_hw_pagetable_enforce_cc(struct
> > > iommufd_hw_pagetable *hwpt)
> > >   */
> > >  struct iommufd_hw_pagetable *
> > >  iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct
> > > iommufd_ioas *ioas,
> > > -                        struct iommufd_device *idev, bool
> > > immediate_attach)
> > > +                        struct iommufd_device *idev,
> > > +                        struct iommufd_hw_pagetable *parent,
> > > +                        union iommu_domain_user_data *user_data,
> > > +                        bool immediate_attach)
> > >  {
> > >       const struct iommu_ops *ops = dev_iommu_ops(idev->dev);
> > > +     struct iommu_domain *parent_domain = NULL;
> > >       struct iommufd_hw_pagetable *hwpt;
> > > +     bool type_unmanaged, type_nested;
> > >       int rc;
> > >
> > >       lockdep_assert_held(&ioas->mutex);
> > >
> > > +     if ((user_data || parent) && !ops->domain_alloc_user)
> > > +             return ERR_PTR(-EOPNOTSUPP);
> >
> > Do we allow specifying parent w/o user_data?
> 
> I don't think so. Perhaps we should do a double check:
> 
> +	if (!!user_data ^ !!parent)
> +		return ERR_PTR(-EINVAL);

I think we allow creating a s2 hwpt with user_data so it
should be:

	if (parent && !user_data)
		return ERR_PTR(-INVAL);

> > > @@ -99,6 +117,15 @@ iommufd_hw_pagetable_alloc(struct
> iommufd_ctx
> > > *ictx, struct iommufd_ioas *ioas,
> > >               goto out_abort;
> > >       }
> > >
> > > +     /* It must be either NESTED or UNMANAGED, depending on
> > > parent_domain */
> > > +       type_nested = hwpt->domain->type == IOMMU_DOMAIN_NESTED;
> > > +       type_unmanaged = hwpt->domain->type ==
> > > IOMMU_DOMAIN_UNMANAGED;
> >
> > no need of one-time used variables. Just put the conditions directly
> > in WARN_ON.
> 
> It is to improve the readability. Otherwise, we'd have:
> 
> 	if (WARN_ON((parent_domain &&
> 		     hwpt->domain->type != IOMMU_DOMAIN_NESTED) ||
> 		    (!parent_domain &&
> 		     hwpt->domain->type !=
> IOMMU_DOMAIN_UNMANAGED)))

IMHO this is already very clear w/o defining additional variables. 😊