RE: [PATCH 3/6] iommu: remove iommu_lookup_page() and the lookup_page() method...

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 26 July 2020 09:28
> To: paul@xxxxxxx
> Cc: 'Andrew Cooper' <andrew.cooper3@xxxxxxxxxx>; 
> xen-devel@xxxxxxxxxxxxxxxxxxxx; Durrant, Paul
> <pdurrant@xxxxxxxxxxxx>; 'Kevin Tian' <kevin.tian@xxxxxxxxx>
> Subject: RE: [EXTERNAL] [PATCH 3/6] iommu: remove iommu_lookup_page() and the 
> lookup_page() method...
> 
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> On 24.07.2020 20:53, Paul Durrant wrote:
> >> From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >> Sent: 24 July 2020 19:39
> >>
> >> On 24/07/2020 17:46, Paul Durrant wrote:
> >>> From: Paul Durrant <pdurrant@xxxxxxxxxx>
> >>>
> >>> ... from iommu_ops.
> >>>
> >>> This patch is essentially a reversion of dd93d54f "vtd: add lookup_page 
> >>> method
> >>> to iommu_ops". The code was intended to be used by a patch that has long-
> >>> since been abandoned. Therefore it is dead code and can be removed.
> >>
> >> And by this, you mean the work that you only partial unstreamed, with
> >> the remainder of the feature still very much in use by XenServer?
> >>
> >
> > I thought we basically decided to bin the original PV IOMMU idea though?
> 
> Did we? It's the first time I hear of it, I think.
> 

I circulated a doc. ages ago, while I was still at Citrix: 
https://docs.google.com/document/d/12-z6JD41J_oNrCg_c0yAxGWg5ADBQ8_bSiP_NH6Hqwo/edit?usp=sharing

In there I propose that we don't follow the original idea of keeping a single 
set of per-domain tables but instead have a set of tables (or IOMMU contexts) 
for groups of devices. 'Context 0' is the current set of static 1:1 tables but 
other contexts are manipulated by hypercall so, in this plan, I don't envisage 
the need to look up mappings in the tables in this way... but I guess I can't 
rule it out.

 Paul