[PATCH 0/2] iommu: Remove iommu_sva_ops::mm_exit()

[Jason Gunthorpe]

On Wed, Apr 08, 2020 at 04:48:02PM -0700, Jacob Pan wrote:
> > Yes, this is the proper way, when the DMA is stopped and no use of the
> > PASID remains then you can drop the mmu notifier and release the PASID
> > entirely. If that is linked to the lifetime of the FD then forget
> > completely about the mm_struct lifetime, it doesn't matter..
> > 
> Got everything above, thanks a lot.
> 
> If everything is in order with the FD close. Why do we need to 
> "ask IOMMU drivers to silently abort DMA and Page Requests in the
> meantime." in mm_exit notifier? This will be done orderly in unbind
> anyway.

I thought this is exactly what Jean-Phillippe is removing here, it is
a bad idea for the reasons he explained.

> > > Enforcing unbind upon FD close might be a precarious path, perhaps
> > > that is why we have to deal with out of order situation?  
> > 
> > How so? You just put it in the FD release function :)
> 
> I was thinking some driver may choose to defer unbind in some workqueue
> etc.

Doesn't really change anything, the lifetime of the PASID wouuld be
the lifetime of the notifier and the bind, and DMA can't continue
without the notifier registered.

Jason