Re: [PATCH 02/23] PVH xen: turn gdb_frames/gdt_ents into union.

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Mon, 5 Aug 2013 16:55:22 +0100
George Dunlap <George.Dunlap@eu.citrix.com> wrote:

> On Sat, Jul 20, 2013 at 2:44 AM, Mukesh Rathor
> <mukesh.rathor@oracle.com> wrote:
> > Changes in V2:
> >   - Add __XEN_INTERFACE_VERSION__
> >
> >   Changes in V3:
> >     - Rename union to 'gdt' and rename field names.
> >
> >   Change in V9:
> >    - Update __XEN_LATEST_INTERFACE_VERSION__ to 0x00040400 for
> > compat.
> >
> > Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
> > Reviewed-by: Jan Beulich <jbeulich@suse.com>
> 
> One thing that's missing here is a description of *why* this change is
> being made.  Seeing that it's introducing a union isn't too difficult;
> harder is figuring out why that's necessary.
> 
> Presumably this is to more closely reflect how an HVM guest's GDT is
> stored -- i.e., in the guest's memory and checked by the hardware on
> use, rather than in Xen's memory, and checked by Xen on assignment?

Right. Unlike PV which passes it's gdt pages to xen to be installed, a
PVH only passes the GDT base and size, as it manages its own GDT. I'll
add more to the comments.

thanks
mukesh