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

[Alex Williamson]

On Wed, 27 Mar 2019 14:17:57 +0000
Parav Pandit <parav@xxxxxxxxxxxx> wrote:

> > -----Original Message-----
> > From: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel-  
> > owner@xxxxxxxxxxxxxxx> On Behalf Of Kirti Wankhede  
> > Sent: Tuesday, March 26, 2019 4:33 AM
> > To: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>; Joerg Roedel <joro@xxxxxxxxxx>;
> > David Woodhouse <dwmw2@xxxxxxxxxxxxx>; Alex Williamson
> > <alex.williamson@xxxxxxxxxx>
> > Cc: ashok.raj@xxxxxxxxx; sanjay.k.kumar@xxxxxxxxx;
> > jacob.jun.pan@xxxxxxxxx; kevin.tian@xxxxxxxxx; Jean-Philippe Brucker <jean-  
> > philippe.brucker@xxxxxxx>; yi.l.liu@xxxxxxxxx; yi.y.sun@xxxxxxxxx;  
> > peterx@xxxxxxxxxx; tiwei.bie@xxxxxxxxx; xin.zeng@xxxxxxxxx;
> > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx; Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>; Neo Jia
> > <cjia@xxxxxxxxxx>
> > 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@xxxxxxxxx>
> > > Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > > Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> > > Cc: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > > Suggested-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> > > Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > > Reviewed-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
> > > ---
> > >  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.

Agreed, if someone wants to fixup before commit or if there's another
spin please do so, otherwise we can adjust it in a trivial follow-up
patch.  Thanks,

Alex