Re: [PATCH 29/38] powerpc: Move 32-bit probe() machine to later in the boot process

On Mon, 2016-06-27 at 22:42 +0200, Gerhard Pircher wrote:

This patch series reminds me of a long-standing issue with the
AmigaOne platform code, which would have to clear the coherence
(M) flag for every memory mapping to avoid lockups (especially
on G4 CPUs) - as you can read in the comment below your patch
above.

Now the follow-up code in amigaone/setup.c to clear the
corresponding CPU feature flag is essentially dead code (it used
to work with a second call of do_feature_fixups() before the
handling of the CPU_FTR_NEED_COHERENT flag was changed/inverted
somewhere around v2.6.30). Also it doesn't seem to fix all
deadlocks, as e.g. KVM virtual machines can still inject memory
mappings with the M flag set AFAICT.

Now I wonder, if there is a reasonably clean way to clear the M
flag in all hardware page table and BAT entries without defacing
generic kernel code too much. Any ideas?

Other than a compile time option ? Do we know where the lockups come
from btw ? A problem with the northbridge ?

Cheers,
Ben.