On Sat, 2010-10-02 at 14:32 -0400, Albert Cahalan wrote: > On the prom boot path, with the firmware supposed to > be managing the MMU, there is a case where: > > 1. Linux changes some BAT registers. > 2. Bits 0x00000070 are/become set in the MSR. > 3. Linux takes an MMU fault.
Meeep ! Linux should never take an MMU fault at that point :-) If it does, then there's a bug somewhere that needs squashing. > 4. The firmware handles it. > > AFAIK, you can't expect the firmware to leave the BAT alone. > If the firmware provides mapping services by using the BAT > as a software-filled TLB, Linux's BAT changes may be lost. > > You also can't expect that your BAT changes will not conflict > with mappings that the firmware uses for itself. The firmware > might write to your new BAT mapping, relying on those virtual > addresses to be something else entirely. Right, which is why the moment Linux takes over the BATs, it shouldn't call into FW anymore nor take faults. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
