Re: [Qemu-devel] ppc: CPU reset must flush translation buffer

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2012-05-21 at 08:15 +0100, Peter Maydell wrote:
> The conclusion we came to is that you only need to tb_flush
> in your CPU's reset function if you have some CPU state which
> you handle by baking it into translated code and doing a tb_flush
> when the state changes. This is relatively rare, most CPU
> frontends only use the other options:
>  (a) CPU state is constant for life of simulation
>  (b) CPU state not baked into code
>  (c) CPU state encoded in tb_flags.
> 
> In particular, target-ppc doesn't have any uses of tb_flush
> at the moment, so either this fix is insufficient (and you need
> to also use tb_flush at the point where the relevant state is
> changed by whatever helper function) or it's the wrong fix.
> 
> If the issue is ROM reloading then the loading code needs to
> be fixed (compare the way that the memory region API correctly
> handles bits of physical memory being mapped/unmapped/remapped
> without the caller needing to do a tb_reset).

Hrm, the state shouldn't change in a drastic way.... we can reproduce
from SLOF which is in real mode and the reset happens in real mode... it
looks like a flush of the exception vectors problem to me.

So that would mean that the ROM reload isn't flushing properly (well,
possibly, need to investigate more). From what I can tell the reload is
done implicitely by generic qemu code creating rom objects when I call
load_image_targphys.

So if something is missing here it's from the generic code, I will dig a
bit more later, gotta take care of sick kids...

Cheers,
Ben.