[PATCH] arc: Re-enable MMU upon die()

[Alexey Brodkin]

Hi Jose,

On Fri, 2017-09-01 at 13:33 +0100, Jose Abreu wrote:
> Hi Alexey,
> 
> On 01-09-2017 12:48, Alexey Brodkin wrote:
> > 
> > Hi Jose,
> > 
> > On Fri, 2017-09-01 at 12:39 +0100, Jose Abreu wrote:
> > > 
> > > I recently came upon a scenario where I would get a double fault
> > > after a machine check error. It turns out that for Ksymbol lookup
> > > to work with modules we need to have MMU enabled because module
> > > address is mapped in the cached space.
> > > 
> > > This patch re-enables the MMU before start printing the stacktrace
> > > making stacktracing of modules work upon a fatal exception.
> > I'm wondering how do we end up with MMU disabled?
> > From ARC700 databook I cannot find any condition on which MMU could be
> > silently disabled by hardware and IIRC there's no code in Linux kernel
> > that disables MMU.
> 
> According to ARC 700 databook a machine check exception causes
> Global TLB enable to be cleared. (See ARC 700 databook, page 687).

Thanks for pointing to that.
I didn't expect to see that note far below "Global TLB enable" bit description.

So then your change makes perfect sense.

Reviwed-by: Alexey Brodkin <abrodkin at synopsys.com>