[Xense-devel] XSM hook for mapping a grant ref

[Derek Murray <Derek.Murray@xxxxxxxxxxxx>]

George et al,

In another thread today, my attention has been drawn to the  
grant_operation_permitted() hook that is called when a domain  
attempts to map a grant reference. This effectively checks whether or  
not the mapping domain has any I/O memory capabilities, and allows  
the mapping if it does. The comment for this macro states that:
"Until TLB flushing issues are sorted out we consider it unsafe for  
domains with no hardware-access privileges to perform grant map/ 
transfer operations."
It seems reasonable that we could have trusted domains which one can  
assume will handle these situations gracefully. Hence, I think there  
is a case for an XSM hook that determines whether or not a domain is  
allowed to map any grants. Arguably, this could be combined with the  
check in xsm_map_grantref, though I would be unsurprised if there is  
a reason for the grant_operation_permitted hook residing where it is  
currently.
This also raises the question of whether XSM should be integrated  
with the existing I/O capabilities system, so that there is one  
consistent view for a domain's privileges.
Regards,

Derek Murray.

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