base-hw & the root task

Neal H. Walfield neal at ...8...
Tue Nov 5 15:59:20 CET 2013

At Tue, 05 Nov 2013 15:15:49 +0100,
Martin Stein wrote:
> The single "kernel"-thread executes solely in privileged CPU mode.
> Initially it disables the MMU and runs in physical address space.
> Before leaving privileged CPU mode the first time, it enables the
> MMU, using the address space of the root-task (core). Thus
> both, threads of the non-privileged root-task and the single "kernel"
> thread use the same virtual address space. For the purpose of
> simplification "kernel" thread and root-task threads also share data
> structures (e.g. raw page-tables or the interrupt-lookup table). This
> must be done carefully because "kernel" thread can always interrupt
> root-task threads and access shared objects without synchronization.

If I understand correctly, you are basically implementing a fail fast
mechanism for the root task.

Thus, the root task can, say, walk the page tables, but to modify the
page tables or to switch protection domains, it traps to the kernel?
Similarly, I'm guessing the kernel doesn't walk any of the root task's
data structure (or, it does so very conservatively).


:) Neal

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