I forgot: On 05.11.2013 15:59, Neal H. Walfield wrote: > 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). > Switching of address spaces is done when switching between privileged and non-privileged mode. When a thread is interrupted by privileged mode, root-task address-space gets applied before the kernel thread is called. As soon as kernel is done and switches back to non-privileged mode, the address space of the currently scheduled non-privileged context is applied. Only in case of a switch between root-task thread and kernel-thread, address space keeps the same.
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