Re: [PATCH v2 2/5] Mini-OS: get own domid

[Julien Grall <julien@xxxxxxx>]

On 13/11/2023 07:37, Jan Beulich wrote:
> On 10.11.2023 18:38, Julien Grall wrote:
> > Hi Jan,
> >
> > On 10/11/2023 12:44, Jan Beulich wrote:
> > > On 10.11.2023 13:23, Roger Pau Monné wrote:
> > > > On Fri, Nov 10, 2023 at 12:34:32PM +0100, Juergen Gross wrote:
> > > > > Get the own domid via creation of a temporary event channel. There is
> > > > > no "official" way to read the own domid in PV guests, so use the event
> > > > > channel interface to get it:
> > > > >
> > > > > - allocate an unbound event channel specifying DOMID_SELF for the
> > > > >     other end
> > > > >
> > > > > - read the event channel status which will contain the own domid in
> > > > >     unbound.dom
> > > > >
> > > > > - close the event channel
> > > > Should we look into introducing a way to expose the domid, so that in
> > > > the future we might not need to resort to this workarounds to get the
> > > > domid?
> > > >
> > > > Maybe in the PV-specific cpuid leaf?  It's a shame we didn't put it in
> > > > a non-HVM specific leaf when it was made available to HVM for pvshim
> > > > reasons.
> > > Couldn't we retroactively generalize the type-agnostic parts of that
> > > leaf?
> > This would only work for x86. I think we want to have a generic
> > hypercalls so it can be used by all arch.
> Hmm, yes, perhaps. Otoh it would seem desirable to me if arch-es also
> provided some extension to an arch-natural way of feature detection
> (which CPUID is on x86), without the need to invoke any hypercalls.
For Arm, I can't really think of anything other than hvc/smc which are 
used for calls to the hypervisor/monitor (so basically hypercalls).
Please suggest if you have a better idea.

Cheers,

--
Julien Grall