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Re: [PATCH] common: don't require use of DOMID_SELF

On 14.01.2021 15:43, Julien Grall wrote:
> On 14/01/2021 14:02, Jan Beulich wrote:
>> It's not overly difficult for a domain to figure out its ID, so
>> requiring the use of DOMID_SELF in a very limited set of places isn't
>> really helpful towards keeping the ID opaque to the guest.
> So I agree that a domid can be figured out really easily today and in 
> principle it would be fine to relax it.
> However, most of the guest OSes will care about running on older Xen 
> versions. Therefore they are not going to be able to use this relaxation.
> So I am not entirely convinced the relaxation is actually worth it for 
> existing hypercalls.

I'm aware of the concern (Andrew has voiced it both here and in
earlier contexts), but personally I think undue restrictions should
not be retained just because they used to be enforced. We've gone
this same route in a few other occasions not overly long ago, and
iirc there are two patches going in a similar direction (different
area of course) that I have still pending and which neither got
ack-ed nor firmly rejected.

> Anyway, if we decide to relax it, then I think we should update the 
> public headers because an OS using this relaxation will not work on 
> older Xen. A developper will not be able to know that without looking at 
> the implementation.

Well, DOMID_SELF exists because that's the preferred form to use.
I can certainly add commentary, but it would feel a little odd to
do so. To be honest I'm also not sure how helpful this is going to
be, considering that consumers often have their own clones of our




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