Subject: Re: [PATCH v2 3/9] powerpc/powernv: Remove real mode access limit for early allocations

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 14 Aug 2017 23:13:07 +1000

On Mon, 2017-08-14 at 22:49 +1000, Michael Ellerman wrote:
> > -     /*
> > -      * We limit the allocation that depend on ppc64_rma_size
> > -      * to first_memblock_size. We also clamp it to 1GB to
> > -      * avoid some funky things such as RTAS bugs.
> 
> That comment about RTAS is 7 years old, and I'm pretty sure it was a
> historical note when it was written.
> 
> I'm inclined to drop it and if we discover new bugs with RTAS on Power9
> then we can always put it back.

Arent' we using a 32-bit RTAS ? (Afaik there's a 64-bit one, we just
never used it ..). In this case we need to at least clamp to 2G (no
trust RTAS doing unsigned properly).

> > -      *
> > -      * On radix config we really don't have a limitation
> > -      * on real mode access. But keeping it as above works
> > -      * well enough.
> 
> Ergh.
> 
> > -      */
> > -     ppc64_rma_size = min_t(u64, first_memblock_size, 0x40000000);
> > -     /*
> > -      * Finally limit subsequent allocations. We really don't want
> > -      * to limit the memblock allocations to rma_size. FIXME!! should
> > -      * we even limit at all ?
> > -      */
> 
> So I think we should just delete this function entirely.
> 
> Any objections?

Well.. RTAS is quite sucky ... 

Ben.

> cheers