Re: [Xen-devel] [PATCH v3 10/13] x86: add iommu_op to enable modification of IOMMU mappings

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jul 20, 2018 at 10:19:44AM +0100, Paul Durrant wrote:
> > >
> > > I think this flag currently serves two purposes: one is to indicate
> > > whether there are resources allocated within xen, the other it indicate
> > > whether it is in use (as suggested in the comment).
> > >
> > > Suppose a domain gets all its devices deassigned after this call,
> > > original iommu_teardown would have been called, but now it won't. The
> > > iommu will still be torn down when it is destroyed, but this is a very
> > > subtle change in behaviour.
> > 
> > That is pretty subtle.
> 
> Actually, thinking a bit more, that is the semantic I want. The domain
> is taking control of its own mappings. It doesn't want Xen to tear
> them down under its feet.

Oh, this makes sense.

> 
> > 
> > >
> > > IMHO we should clearly separate these two cases if possible.
> > >
> > 
> > Agreed. I never liked the 'need_iommu' name anyway. I'll add a patch before
> > this one to do the rename/split.
> > 
> 
> I still think this renaming/clarification is worthwhile so I'll still
> add something into the series.
> 

Thanks.

Wei.

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