bogus check in get_page_from_l1e()?

["Jan Beulich" <JBeulich@novell.com>]

Keir,

in the I/O page code path, we have

        if ( !iomem_access_permitted(pg_owner, mfn, mfn) )
        {
            if ( mfn != (PADDR_MASK >> PAGE_SHIFT) ) /* INVALID_MFN? */
                MEM_LOG("Non-privileged (%u) attempt to map I/O space %08lx", 
                        pg_owner->domain_id, mfn);
            return 0;
        }

What is the reason to suppress the warning for the one specific
(PADDR_MASK >> PAGE_SHIFT) MFN value, i.e. where could this
validly come from and hence warrant not to issue the warning?

Also, the message seems to be having the potential of being
misleading (these days at least, but perhaps it always was), as
it clearly is possible for Dom0 to also be denied a mapping here
(and hence the "Non-privileged" can be wrong).

Bottom line question: Should we issue the warning unconditionally,
just stating the domain ID?

Thanks, Jan