linux-kernel - RE: [PATCH v1 3/8] iommufd: Create access in vfio_iommufd_emulated

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Message-ID: <BN9PR11MB5276721CE80769AEC8590D7F8CD79@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 3 Feb 2023 09:28:03 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.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>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "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>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH v1 3/8] iommufd: Create access in
 vfio_iommufd_emulated_bind()

> From: Tian, Kevin
> Sent: Friday, February 3, 2023 5:24 PM
> 
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Thursday, February 2, 2023 3:05 PM
> >
> > To prepare for an access->ioas replacement, move
> iommufd_access_create()
> > call into vfio_iommufd_emulated_bind(), making it symmetric with the
> > __vfio_iommufd_access_destroy() call in
> vfio_iommufd_emulated_unbind().
> > This means an access is created/destroyed by the bind()/unbind(), and the
> > vfio_iommufd_emulated_attach_ioas() only updates the access->ioas
> pointer.
> >
> > Since there's no longer an ioas_id input for iommufd_access_create(), add
> > a new helper iommufd_access_set_ioas() to set access->ioas. We can later
> > add a "replace" feature simply to the new iommufd_access_set_ioas() too.
> >
> > Leaving the access->ioas in vfio_iommufd_emulated_attach_ioas(),
> however,
> > can introduce some potential of a race condition during pin_/unpin_pages()
> > call where access->ioas->iopt is getting referenced. So, add an ioas_lock
> > to protect it.
> >
> 
> What about introducing another flag e.g. vdev->iommufd_access_attached
> which got set in vfio_iommufd_emulated_attach_ioas() to fulfill what
> vdev->iommufd_access guards today?

Obviously this doesn't work with what 'replace' requires in following
patches. So please just ignore this comment...