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

[Jan Beulich <jbeulich@suse.com>]

On 14.01.2021 16:01, Andrew Cooper wrote:
> On 14/01/2021 14:02, Jan Beulich wrote:
>> --- a/xen/common/page_alloc.c
>> +++ b/xen/common/page_alloc.c
>> @@ -2566,13 +2566,7 @@ __initcall(register_heap_trigger);
>>  
>>  struct domain *get_pg_owner(domid_t domid)
>>  {
>> -    struct domain *pg_owner = NULL, *curr = current->domain;
>> -
>> -    if ( unlikely(domid == curr->domain_id) )
>> -    {
>> -        gdprintk(XENLOG_WARNING, "Cannot specify itself as foreign domain\n");
>> -        goto out;
>> -    }
>> +    struct domain *pg_owner;
> 
> I'm not sure this is correct.
> 
> It isn't a DOMID_SELF check.  It's a "confirm the nominated domid is
> remote" check, and I don't see all the callers of this interface having
> appropriate checks to prohibit trying to do a foreign operation on
> oneself, however they specify the foreign domid.

Since Julien had me look up all the call sites anyway (for adding
respective commentary in the public headers), I checked this
property as well: The only case where a foreign domain is strictly
required is the handling of XENMAPSPACE_gmfn_foreign, and there a
respective check exists.

I actually question do_mmuext_op()'s use of the function, as
neither DOMID_IO nor DOMID_XEN ought to be sensibly usable there.

Jan