This pointer is valid as long as SUPLib has a open session. Anyone using the page must treat this pointer as higly volatile and not trust it beyond one transaction.
The GIP page is read-only to everyone but the support driver and is actually mapped read only everywhere but in ring-0. However it is not marked 'const' as this might confuse compilers into thinking that values doesn't change even if members are marked as volatile. Thus, there is no PCSUPGLOBALINFOPAGE type.