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Re: [Xen-devel] [PATCH 4/8] viridian: remove duplicate union types

> -----Original Message-----
> From: Roger Pau Monne
> Sent: 30 October 2018 16:40
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Jan Beulich
> <jbeulich@xxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH 4/8] viridian: remove duplicate union
> types
> On Mon, Oct 29, 2018 at 06:02:07PM +0000, Paul Durrant wrote:
> > The 'viridian_vp_assist', 'viridian_hypercall_gpa' and
> > 'viridian_reference_tsc' union types are identical in layout. The layout
> > is also common throughout the specification [1].
> >
> > This patch declares a common 'viridian_page_msr' type and converts the
> rest
> > of the code to use that type for both the hypercall and VP assist pages.
> I agree with the unification of the viridian_page_msr struct.
> > Also, rename 'viridian_guest_os_id' to 'viridian_guest_os_id_msr' since
> it
> > also is a union representing an MSR value.
>                                ^ a
> IMO (and I'm not that familiar with the code) adding those _msr
> prefixes here doesn't seem to add any value to the code, there's
> nothing MSR specific in those structs, apart from their size.

There is actually... they are unions that represent the layout of an MSR, e.g 
See section 2.6 "Reporting the Guest OS Identity".

> Is there a plan to add a new structure like viridian_page_mmio or
> similar that requires such prefixes to be present?

No, I'm not anticipating Windows communicating via an MMIO region, but I's 
still like the call out something that represents a bit-field encoding of an 


> Thanks, Roger.

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