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

  • To: Julien Grall <julien@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Mon, 13 Nov 2023 08:37:55 +0100
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  • Cc: minios-devel@xxxxxxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, samuel.thibault@xxxxxxxxxxxx, wl@xxxxxxx, Juergen Gross <jgross@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Mon, 13 Nov 2023 07:38:02 +0000
  • List-id: Mini-os development list <minios-devel.lists.xenproject.org>

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.




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