[PATCH v2 2/2] vfio: Replace the iommu notifier with a device list

[Tian, Kevin]

> From: Jason Gunthorpe <jgg at nvidia.com>
> Sent: Wednesday, June 8, 2022 7:27 PM
> 
> On Wed, Jun 08, 2022 at 03:47:12AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe
> > > Sent: Wednesday, June 8, 2022 7:02 AM
> > >
> > > Instead of bouncing the function call to the driver op through a blocking
> > > notifier just have the iommu layer call it directly.
> > >
> > > Register each device that is being attached to the iommu with the lower
> > > driver which then threads them on a linked list and calls the appropriate
> > > driver op at the right time.
> > >
> > > Currently the only use is if dma_unmap() is defined.
> > >
> > > Also, fully lock all the debugging tests on the pinning path that a
> > > dma_unmap is registered.
> > >
> > ...
> > > Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>
> > > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > > b/drivers/vfio/vfio_iommu_type1.c
> > > index c13b9290e35759..4ddb1f1abd238b 100644
> > > +++ b/drivers/vfio/vfio_iommu_type1.c
> > > @@ -67,7 +67,8 @@ struct vfio_iommu {
> > >  	struct list_head	iova_list;
> > >  	struct mutex		lock;
> > >  	struct rb_root		dma_list;
> > > -	struct blocking_notifier_head notifier;
> > > +	struct list_head	device_list;
> > > +	struct mutex		device_list_lock;
> >
> > emulated_device_list or unmap_device_list, to be more accurate?
> 
> I don't think it is worth getting too specific here, the fact it only
> has dma_unmap devices is a bit of a shortcut to save some work.
> 
> > btw a few lines downward there is already a emulated_iommu_groups.
> > the two sounds a bit overlapping given mdev's iommu group is faked
> > and singleton. Wonder whether it's cleaner to just reuse the existing field...
> 
> The locking is more complicated on this since we still have check
> every device in the group if it is opened or not while launching the
> callback and prevent it from opening/closing while the callback is
> running.
> 
> Since I plan to delete the dirty tracking which will drop the
> emulated_iommu_groups too I would leave it like this.
> 

Make sense.

Reviewed-by: Kevin Tian <kevin.tian at intel.com>