Re: [Xen-devel] [PATCH 08/18] xen: Add DOMID_SELF support to rcu_lock_domain_by_id

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.08.12 at 17:19, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
> On 08/06/2012 11:07 AM, Jan Beulich wrote:
>>>>> On 06.08.12 at 16:32, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
>>> Callers that want to prevent use of DOMID_SELF already need to ensure
>>> the calling domain does not pass its own domain ID. This removes the
>>> need for the caller to manually support DOMID_SELF, which many already
>>> do.
>> 
>> I'm not really sure this is correct. At the very least it changes the
>> return value of rcu_lock_remote_target_domain_by_id() when
>> called with DOMID_SELF (from -ESRCH to -EPERM).
> 
> This series ends up eliminating that function in patch #18, so that
> part is taken care of.

But may, in case of problems, then not be fully bi-sectable.

>> I'm also not convinced that a distinction between a domain knowing
>> its ID and one passing DOMID_SELF isn't/can't be useful. That of
>> course depends on whether the ID can be fully hidden from a guest
>> (obviously pure HVM guests would never know their ID, but then
>> again they also would never pass DOMID_SELF anywhere; it might
>> be, however, that they could get the latter passed on their behalf
>> e.g. from some emulation function).
> 
> I don't think we can (or want to) make it impossible for a guest to find
> out its own domain ID. I agree that the distinction between DOMID_SELF and
> my_own_domid can be a useful distinction in some cases. Most of those cases
> in Xen that I have seen already handle this at the caller.
> 
> Another solution here is to create a function rcu_lock_domain_by_any_id that
> is identical to rcu_lock_domain_by_id except for handling DOMID_SELF.

Maybe. I'd like to see Keir's position regarding all of the details
here anyway.

Jan


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