linux-kernel - Re: [PATCH v2 06/11] iommufd: IOMMU_HWPT

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Message-ID: <ZG2jWQvl9tdpZ1Vv@Asurada-Nvidia>
Date:   Tue, 23 May 2023 22:40:41 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
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        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
Subject: Re: [PATCH v2 06/11] iommufd: IOMMU_HWPT_ALLOC allocation with user
 data

On Wed, May 24, 2023 at 05:16:35AM +0000, Tian, Kevin wrote:
 
> > From: Nicolin Chen <nicolinc@...dia.com>
> > 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