Phillip Susi wrote:
Hrm... are you saying that the page tables are shared, but since the page directory is not, a page fault can happen because the current processes' page directory does not contain a PDE yet pointing to the page table? That makes sense, but the page fault handler should notice that the fault happened because the PDE is missing, and just copy the PDE (if it exists) from the system process page directory. As long as the page fault handler does that, then the process management code will not need to do anything special.
Currently there exist two problems which cannot resolved by the trap/page fault handler. The trap handler is invoked before the page fault handler. The trap handler checks always for a stack under flow and use the current thread entry from the pcr (PsGetCurrentThread). This means, a page fault from the pcr's current thread entry cannot be handled. While the thread switch code is execute, interrupts are only disabled while the kernel stack is switched. There is a gap between switching the stack and switching the page table. If the pde for the new stack isn't valid for the old thread and the stack is accessed (by an interrupt or a trap), it does occur a double fault.
- Hartmut