Re: [Xen-devel] [PATCH] iommu: specify page_count rather than page_order to iommu_map/unmap()...

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 21 January 2019 11:28
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; Roger Pau Monne <roger.pau@xxxxxxxxxx>; Wei
> Liu <wei.liu2@xxxxxxxxxx>; Sander Eikelenboom <linux@xxxxxxxxxxxxxx>;
> George Dunlap <George.Dunlap@xxxxxxxxxx>; Ian Jackson
> <Ian.Jackson@xxxxxxxxxx>; Chao Gao <chao.gao@xxxxxxxxx>; Jun Nakajima
> <jun.nakajima@xxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>; Stefano
> Stabellini <sstabellini@xxxxxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>; Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>
> Subject: Re: [PATCH] iommu: specify page_count rather than page_order to
> iommu_map/unmap()...
> 
> >>> On 18.01.19 at 17:03, <paul.durrant@xxxxxxxxxx> wrote:
> > ...and remove alignment assertions.
> >
> > Testing shows that certain callers of iommu_legacy_map/unmap() specify
> > order > 0 ranges that are not order aligned thus causing one of the
> > IS_ALIGNED() assertions to fire.
> 
> As said before - without a much better explanation of why the current
> order-based model is unsuitable (so far I've been provided only vague
> pointers into "somewhere in PVH Dom0 boot code" iirc) to understand
> why it's undesirable to simply make those call sites obey to the current
> requirements, I'm not happy to see us go this route.

I thought...

"Using a count actually makes more sense because the valid
set of mapping orders is specific to the IOMMU implementation and to it
should be up to the implementation specific code to translate a mapping
count into an optimal set of mapping orders (when the code is finally
modified to support orders > 0)."

...was reasonably clear. Is that not a reasonable justification? What else 
could I say?

  Paul

> 
> Jan
> 


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