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

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