linux-kernel - Re: [PATCH v7 7/9] vfio/mdev: Add iommu related member in mdev

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Date:   Fri, 22 Feb 2019 08:31:01 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Kirti Wankhede <kwankhede@...dia.com>, kevin.tian@...el.com,
        ashok.raj@...el.com, tiwei.bie@...el.com,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        sanjay.k.kumar@...el.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, yi.y.sun@...el.com,
        jacob.jun.pan@...el.com, kvm@...r.kernel.org
Subject: Re: [PATCH v7 7/9] vfio/mdev: Add iommu related member in
 mdev_device

On Fri, 22 Feb 2019 06:34:38 -0800
Christoph Hellwig <hch@...radead.org> wrote:

> On Fri, Feb 22, 2019 at 10:19:25AM +0800, Lu Baolu wrote:
> > A parent device might create different types of mediated
> > devices. For example, a mediated device could be created
> > by the parent device with full isolation and protection
> > provided by the IOMMU. One usage case could be found on
> > Intel platforms where a mediated device is an assignable
> > subset of a PCI, the DMA requests on behalf of it are all
> > tagged with a PASID. Since IOMMU supports PASID-granular
> > translations (scalable mode in VT-d 3.0), this mediated
> > device could be individually protected and isolated by an
> > IOMMU.
> > 
> > This patch adds a new member in the struct mdev_device to
> > indicate that the mediated device represented by mdev could
> > be isolated and protected by attaching a domain to a device
> > represented by mdev->iommu_device. It also adds a helper to
> > add or set the iommu device.
> > 
> > * mdev_device->iommu_device
> >   - This, if set, indicates that the mediated device could
> >     be fully isolated and protected by IOMMU via attaching
> >     an iommu domain to this device. If empty, it indicates
> >     using vendor defined isolation, hence bypass IOMMU.
> > 
> > * mdev_set/get_iommu_device(dev, iommu_device)
> >   - Set or get the iommu device which represents this mdev
> >     in IOMMU's device scope. Drivers don't need to set the
> >     iommu device if it uses vendor defined isolation.
> > 
> > Cc: Ashok Raj <ashok.raj@...el.com>
> > Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > Cc: Kevin Tian <kevin.tian@...el.com>
> > Cc: Liu Yi L <yi.l.liu@...el.com>
> > Suggested-by: Kevin Tian <kevin.tian@...el.com>
> > Suggested-by: Alex Williamson <alex.williamson@...hat.com>
> > Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> > Reviewed-by: Jean-Philippe Brucker <jean-philippe.brucker@....com>
> > ---
> >  drivers/vfio/mdev/mdev_core.c    | 18 ++++++++++++++++++
> >  drivers/vfio/mdev/mdev_private.h |  1 +
> >  include/linux/mdev.h             | 14 ++++++++++++++
> >  3 files changed, 33 insertions(+)
> > 
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index 0212f0ee8aea..9be58d392d2b 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -390,6 +390,24 @@ int mdev_device_remove(struct device *dev, bool force_remove)
> >  	return 0;
> >  }
> >  
> > +int mdev_set_iommu_device(struct device *dev, struct device *iommu_device)
> > +{
> > +	struct mdev_device *mdev = to_mdev_device(dev);
> > +
> > +	mdev->iommu_device = iommu_device;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(mdev_set_iommu_device);  
> 
> As said before, please make all new mdev/vfio exports EXPORT_SYMBOL_GPL
> to fit the other exports in vfio.

Well...

$ grep EXPORT_SYMBOL drivers/vfio/mdev/*
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_parent_dev);
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_get_drvdata);
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_set_drvdata);
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_dev);
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_from_dev);
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_uuid);
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_register_device);
drivers/vfio/mdev/mdev_core.c:EXPORT_SYMBOL(mdev_unregister_device);
drivers/vfio/mdev/mdev_driver.c:EXPORT_SYMBOL_GPL(mdev_bus_type);
drivers/vfio/mdev/mdev_driver.c:EXPORT_SYMBOL(mdev_register_driver);
drivers/vfio/mdev/mdev_driver.c:EXPORT_SYMBOL(mdev_unregister_driver);

For better or worse, the mdev interface does allow non-GPL vendor
drivers.  This export seems consistent with that, it's a simple
association allowing the vendor driver to define an IOMMU API backing
device for an mdev device.  I don't think this association implies
sufficient operational knowledge to require a GPL symbol and it's been
requested for use by one of those non-GPL mdev vendor drivers,
therefore I support this definition.  Thanks,

Alex