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

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Date:   Fri, 3 Feb 2023 09:23:32 +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: 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?