Re: [Xen-devel] [PATCH v5 06/15] public / x86: introduce __HYPERCALL_iommu_op

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx]
> Sent: 07 August 2018 04:00
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>;
> Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Ian Jackson
> <Ian.Jackson@xxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>; Jan Beulich
> <jbeulich@xxxxxxxx>; Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> Subject: RE: [Xen-devel] [PATCH v5 06/15] public / x86: introduce
> __HYPERCALL_iommu_op
> 
> > From: Paul Durrant
> > Sent: Saturday, August 4, 2018 1:22 AM
> >
> > This patch introduces the boilerplate for a new hypercall to allow a
> > domain to control IOMMU mappings for its own pages.
> > Whilst there is duplication of code between the native and compat entry
> > points which appears ripe for some form of combination, I think it is
> > better to maintain the separation as-is because the compat entry point
> > will necessarily gain complexity in subsequent patches.
> >
> > NOTE: This hypercall is only implemented for x86 and is currently
> >       restricted by XSM to dom0. Its scope can be expanded in future
> >       if need be.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> [...]
> 
> > diff --git a/xen/arch/x86/iommu_op.c b/xen/arch/x86/iommu_op.c
> > new file mode 100644
> > index 0000000000..744c0fce27
> > --- /dev/null
> > +++ b/xen/arch/x86/iommu_op.c
> > @@ -0,0 +1,184 @@
> >
> +/*********************************************************
> ***
> > ******************
> > + * x86/iommu_op.c
> > + *
> > + * Paravirtualised IOMMU functionality
> 
> although only x86 is supported, logic in this file is vendor agnostic. Better
> move to a common place now...
> 

Personally I don't like to expand scope into architectures which I have no 
facility to test.  IIUC ARM also very much relies on an identity GFN:BFN map so 
this functionality is unlikely to get used by anything other than x86 for the 
foreseeable future.

Julien, would you prefer that this be in common code?

  Paul

> Thanks
> Kevin
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