The new core-internal 'Address_space' interface enables cores RM service
to flush mappings of a PD in which a given 'Rm_client' thread resides.
Prior this patch, each platform invented their own way to flush mappings
in the respective 'rm_session_support.cc' implementation. However, those
implementations used to deal poorly with some corner cases. In
particular, if a PD session was destroyed prior a RM session, the RM
session would try to use no longer existing PD session. The new
'Address_space' uses the just added weak-pointer mechanism to deal with
this issue.
Furthermore, the generic 'Rm_session_component::detach' function has
been improved to avoid duplicated unmap operations for platforms that
implement the 'Address_space' interface. Therefore, it is related to
issue #595. Right now, this is OKL4 only, but other platforms will follow.
The kernel distinguishes local from global IDs by looking at the lowest
6 bits of the thread ID (i.e., in 'L4_ThreadControl'). If those bits are
zero, the ID is interpreted as a local ID. Because those zero bits
overlap with the version bits of global IDs, this invariant could be
violated once the version of a global ID reaches 64. In this case,
'L4_ThreadControl' will return an error on the attempt to create a new
PD. To prevent this from happening, we always set the lowest bit to 1.
Martin Stein
Norman Feske
Genode Labs