linux-kernel - RE: [PATCH v10 3/6] iommufd: Add iommufd_access_change_ioas(

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Message-ID: <BN9PR11MB5276C3F296F27696AFD92D0F8C06A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 28 Jul 2023 04:41:18 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>
CC:     "jgg@...dia.com" <jgg@...dia.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "farman@...ux.ibm.com" <farman@...ux.ibm.com>
Subject: RE: [PATCH v10 3/6] iommufd: Add iommufd_access_change_ioas(_id)
 helpers

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Friday, July 28, 2023 12:37 PM
> 
> On Fri, Jul 28, 2023 at 04:23:03AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > > Sent: Friday, July 28, 2023 4:25 AM
> > >
> > > +static int iommufd_access_change_ioas(struct iommufd_access *access,
> > > +                                   struct iommufd_ioas *new_ioas)
> > > +{
> > > +     u32 iopt_access_list_id = access->iopt_access_list_id;
> > > +     struct iommufd_ioas *cur_ioas = access->ioas;
> > > +     int rc;
> > > +
> > > +     lockdep_assert_held(&access->ioas_lock);
> > > +
> > > +     /* We are racing with a concurrent detach, bail */
> > > +     if (cur_ioas != access->ioas_unpin)
> > > +             return -EBUSY;
> > > +
> > > +     if (IS_ERR(new_ioas))
> > > +             return PTR_ERR(new_ioas);
> >
> > iommufd_access_change_ioas_id() already checks errors.
> 
> I've thought about that: given that iommufd_access_change_ioas
> is a standalone API, though it's not used anywhere else at the
> moment, it might be safer to have this check again. Otherwise,
> we would need a line of comments saying that "caller must make
> sure that the input new_ioas is not holding an error code" or
> so?
> 

I don't think it's a common practice for the caller to pass in
an error pointer when it already knows it's an error...