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

[Nicolin Chen <nicolinc@nvidia.com>]

On Wed, May 24, 2023 at 05:11:43AM +0000, Tian, Kevin wrote:
 
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > 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);

Oh, yes. I forgot about that :)

> > > > @@ -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. 😊

Okay. I think we can revert this back and drop the two type_*.

Thanks
Nic