[PATCH] powerpc/pseries: Fix MCE handling on pseries

[Nicholas Piggin]

Ganesh Goudar's on March 14, 2020 12:04 am:
> MCE handling on pSeries platform fails as recent rework to use common
> code for pSeries and PowerNV in machine check error handling tries to
> access per-cpu variables in realmode. The per-cpu variables may be
> outside the RMO region on pSeries platform and needs translation to be
> enabled for access. Just moving these per-cpu variable into RMO region
> did'nt help because we queue some work to workqueues in real mode, which
> again tries to touch per-cpu variables.

Which queues are these? We should not be using Linux workqueues, but the
powerpc mce code which uses irq_work.

> Also fwnmi_release_errinfo()
> cannot be called when translation is not enabled.

Why not?

> This patch fixes this by enabling translation in the exception handler
> when all required real mode handling is done. This change only affects
> the pSeries platform.

Not supposed to do this, because we might not be in a state
where the MMU is ready to be turned on at this point.

I'd like to understand better which accesses are a problem, and whether
we can fix them all to be in the RMO.

Thanks,
Nick