Re: [PATCH v2 06/11] iommufd: IOMMU_HWPT_ALLOC allocation with user data

[Nicolin Chen]

On Wed, May 24, 2023 at 05:16:35AM +0000, Tian, Kevin wrote:
 
> > From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > Sent: Saturday, May 20, 2023 3:48 AM
> >
> >
> > > >
> > > > +     switch (pt_obj->type) {
> > > > +     case IOMMUFD_OBJ_IOAS:
> > > > +             ioas = container_of(pt_obj, struct iommufd_ioas, obj);
> > > > +             break;
> > >
> > > this should fail if parent is specified.
> >
> > I don't think that's necessaray: the parent is NULL by default
> > and only specified (if IOMMUFD_OBJ_HW_PAGETABLE) by the exact
> > pt_id/pt_obj here.
> 
> I didn't get. The uAPI describes that only hwpt not ioas can be specified
> in the pt_id field as the parent.
>
> If we don't check here it means the user can specify an ioas id as the
> parent?

I meant that the parent pointer isn't specified at this line:
the declaration of the parent is simply NULL, and not touched
in this IOMMUFD_OBJ_IOAS case, as the parent pointer would be
only specified in the IOMMUFD_OBJ_HW_PAGETABLE case that is
behind this line.

We could add a sanity of the parent pointer, but that would
be just a NOP, right?

Thanks
Nic