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Re: [PATCH v2 2/5] Mini-OS: get own domid
Hi,
On 13/11/2023 09:28, Jan Beulich wrote:
On 13.11.2023 10:12, Julien Grall wrote:
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.
I don't know enough Arm to properly suggest something. Arm64 has various
id_* system registers, so I would be wondering whether having a properly
virtual one reserved in system register space couldn't do the trick.
AFAIK there are none available. But if such exists, then I don't see how
that would suit with my requests to have an arch-agnostic approach.
Each architecture would need to have to provide a way to expose those
values. At which point, why not using hypercall? What's wrong with it?
Cheers,
--
Julien Grall
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