Re: [PATCH] powerpc: don't select KFENCE on platform PPC_FSL_BOOK3E

[Christophe Leroy]

Le 13/10/2021 à 02:48, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> > Le 12/10/2021 à 08:24, Michael Ellerman a écrit :
> > > Liu Shixin <liushixin2@xxxxxxxxxx> writes:
> > > > 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.

No problem.


> > 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.


We also have a problem with STRICT_KERNEL_RWX as it is based on the same 
principles until someone implements it by blocks like book3s/32 and 8xx.

So it should also be unselectable on e500 and 44x for now.

Christophe