Christophe Leroy [off-list ref] writes:
Le 12/10/2021 à 08:24, Michael Ellerman a écrit :
quoted
Liu Shixin [off-list ref] writes:
quoted
kindly ping.
I was under the impression you were trying to debug why it wasn't
working with Christophe.
The investigation was a bit dormant to be honest since Liu confirmed
that neither KFENCE not DEBUG_PAGEALLOC works.
No worries. Sorry it fell to you to do the investigation.
I now looked at the effort to make it work, and it is not trivial.
At the time being, all linear space is mapped with pinned TLBs and
everything is setup for space 0, with space 1 being used temporarily
when doing heavy changes to space 0.
We can't use standard pages for linear space on space 0 because we need
memory mapped at all time for exceptions (on booke exception run with
MMU on in space 0).
In order to use standard pages, we'd need to reorganise the kernel to
have it run mostly in space 1 (for data at least) where we would map
almost everything with standard pages, and keep pinned TLB to map linear
space on space 0 for TLB miss exceptions. Then we'd do more or less like
book3s/32 and switch back into space 1 into other exceptions prolog.
That could be good to do it as we could maybe have more code in common
with non booke 32 bits, but it is not a trivial job.
So I suggest that for now, we just make KFENCE and DEBUG_PAGEALLOC
unselectable for booke/32 (e500 and 44x).
Yep seems reasonable.
cheers