Re: [PATCH v5 02/25] iommu/sva: Manage process address spaces

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On Thu, Apr 16, 2020 at 05:13:31AM -0700, Christoph Hellwig wrote:
> On Thu, Apr 16, 2020 at 10:54:02AM +0200, Jean-Philippe Brucker wrote:
> > On Thu, Apr 16, 2020 at 12:28:52AM -0700, Christoph Hellwig wrote:
> > > > +	rcu_read_lock();
> > > > +	hlist_for_each_entry_rcu(bond, &io_mm->devices, mm_node)
> > > > +		io_mm->ops->invalidate(bond->sva.dev, io_mm->pasid, io_mm->ctx,
> > > > +				       start, end - start);
> > > > +	rcu_read_unlock();
> > > > +}
> > > 
> > > What is the reason that the devices don't register their own notifiers?
> > > This kinds of multiplexing is always rather messy, and you do it for
> > > all the methods.
> > 
> > This sends TLB and ATC invalidations through the IOMMU, it doesn't go
> > through device drivers
> 
> I don't think we mean the same thing, probably because of my rather
> imprecise use of the word device.
> 
> What I mean is that the mmu_notifier should not be embedded into the
> io_mm structure (whch btw, seems to have a way to generic name, just
> like all other io_* prefixed names), but instead into the
> iommu_bond structure.  That avoid the whole multiplexing layer.

Right, I can see the appeal. I still like having a single mmu notifier per
mm because it ensures we allocate a single PASID per mm (as required by
x86). I suppose one alternative is to maintain a hashtable of mm->pasid,
to avoid iterating over all bonds during allocation.

Thanks,
Jean



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