Re: [PATCH v1 07/14] vfio: Add a device notifier interface

[Jason Gunthorpe]

On Tue, Mar 09, 2021 at 08:45:13AM -0700, Alex Williamson wrote:

> > I'm having trouble guessing why we need to refcount the group to add a
> > notifier to the device's notifier chain? 
> > 
> > I suppose it actually has to do with the MMIO mapping? But I don't
> > know what the relation is between MMIO mappings in the IOMMU and the
> > container? This could deserve a comment?
> 
> Sure, I can add a comment.  We want to make sure the device remains
> within an IOMMU context so long as we have a DMA mapping to the device
> MMIO, which could potentially manipulate the device.  IOMMU context is
> managed a the group level.

I find refcounting is easier to understand if the refcount inc/dec is
near the thing that is actually using the object - so I'd suggest to
move this to the iommu code.

A comment sounds like a good idea since this is security sensitive

Jason