RE: [PATCH v8 7/9] vfio/mdev: Add iommu related member in mdev_device

[Parav Pandit <parav@mellanox.com>]

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org <linux-kernel-
> owner@vger.kernel.org> On Behalf Of Kirti Wankhede
> Sent: Tuesday, March 26, 2019 4:33 AM
> To: Lu Baolu <baolu.lu@linux.intel.com>; Joerg Roedel <joro@8bytes.org>;
> David Woodhouse <dwmw2@infradead.org>; Alex Williamson
> <alex.williamson@redhat.com>
> Cc: ashok.raj@intel.com; sanjay.k.kumar@intel.com;
> jacob.jun.pan@intel.com; kevin.tian@intel.com; Jean-Philippe Brucker <jean-
> philippe.brucker@arm.com>; yi.l.liu@intel.com; yi.y.sun@intel.com;
> peterx@redhat.com; tiwei.bie@intel.com; xin.zeng@intel.com;
> iommu@lists.linux-foundation.org; kvm@vger.kernel.org; linux-
> kernel@vger.kernel.org; Jacob Pan <jacob.jun.pan@linux.intel.com>; Neo Jia
> <cjia@nvidia.com>
> Subject: Re: [PATCH v8 7/9] vfio/mdev: Add iommu related member in
> mdev_device
> 
> 
> 
> On 3/25/2019 7:00 AM, 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@intel.com>
> > Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Cc: Kevin Tian <kevin.tian@intel.com>
> > Cc: Liu Yi L <yi.l.liu@intel.com>
> > Suggested-by: Kevin Tian <kevin.tian@intel.com>
> > Suggested-by: Alex Williamson <alex.williamson@redhat.com>
> > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> > Reviewed-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.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 b96fedc77ee5..1b6435529166
> > 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);
> > +
> > +struct device *mdev_get_iommu_device(struct device *dev) {
> > +	struct mdev_device *mdev = to_mdev_device(dev);
> > +
> > +	return mdev->iommu_device;
> > +}
> > +EXPORT_SYMBOL(mdev_get_iommu_device);
> > +
> >  static int __init mdev_init(void)
> >  {
> >  	return mdev_bus_register();
> > diff --git a/drivers/vfio/mdev/mdev_private.h
> > b/drivers/vfio/mdev/mdev_private.h
> > index 379758c52b1b..bfb7b22a7cb6 100644
> > --- a/drivers/vfio/mdev/mdev_private.h
> > +++ b/drivers/vfio/mdev/mdev_private.h
> > @@ -34,6 +34,7 @@ struct mdev_device {
> >  	struct list_head next;
> >  	struct kobject *type_kobj;
> >  	bool active;
> > +	struct device *iommu_device;
> >  };
> >
This is not a performance path, but it is a good practice to create naturally aligned/packed structures.
You should define struct device *iommu_device; before bool active.