Re: [Xen-devel] [PATCH v5 12/15] x86: add iommu_op to enable modification of IOMMU mappings

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx]
> Sent: 07 August 2018 10:20
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Tim
> (Xen.org) <tim@xxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>;
> Julien Grall <julien.grall@xxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Ian
> Jackson <Ian.Jackson@xxxxxxxxxx>
> Subject: RE: [Xen-devel] [PATCH v5 12/15] x86: add iommu_op to enable
> modification of IOMMU mappings
> 
> > From: Paul Durrant [mailto:Paul.Durrant@xxxxxxxxxx]
> > Sent: Tuesday, August 7, 2018 5:12 PM
> >
> >
> > > So here current version pvIOMMU only provides global address space,
> > > though unlike any existing IOMMU. maybe we should explicitly call out
> > > this fact in some capability field for future extension.
> > >
> >
> > Does Linux expose such a thing through the dma_ops? I didn't see one, but
> > if there is one then we can of course set it correctly according to the
> > limitations of the underying hypervisor. Thus, if Xen is modified in future 
> > to
> > support per-device mappings, this could be exposed through to the drivers
> > using DMA.
> >
> 
> not about Linux internal exposing. it's about hypervisor exposing
> the capability to pvIOMMU driver, so the latter knows whether to
> enable per-device mapping. But as you commented in another
> mail, it could be achieved through enabling sequence.
> 

Ok. Let's go with that then.

> btw could you put clarification according to our discussions in your
> next version coverletter to set the tone clear from start? I don't
> think I'll be the only one interpreting wrong goal for this work. :-)
> 

I can certainly do that. I'll put an explanation of the XenServer use-case in 
as a concrete example too.

  Paul

> Thanks
> Kevin
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