RMGR-Extension to control I/O access

[Michael Hohmuth]

Christian Stueble <stueble at amaunet.cs.uni-dortmund.de> writes:

> > That is exactly what io flex pages are designed for. Initially sigma0
> > has access to all io ports and can use io flex pages to grant port
> > access to other task. If sigma0 grants access a subset of the io
> > address space (adressses which are accessed by in/out instructions)
> > the task gets an io permission bitmap. If sigma0 (or someone else)
> > grants access to the whole io address space l4 changes the iopl so
> > that any thread in this task can access any port and can even disable
> > interrupts.

> I understand the x86 manual in that way: i/o access is permitted only if the
> tasks CPL <= IOPL _and_ if appropriated bits are set to 0.

No, that´s ``or,´´ not ``and.´´

> Generally, only two new IPC messages (to the RMGR or sigma0?) are
> necessary:

Rmgr

> 1) demandPort( port_nr, size )
> 2) releasePort( port_nr, size )

Yes, that´s right.

> Does someone know, why the l4 reference manual restricts the granularity of
> port access to 16 byte?

No, I don´t.  Maybe Jochen can shed some light on this?

Michael
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