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

On Tue, 2017-08-15 at 22:10 +1000, Nicholas Piggin wrote:

On Mon, 14 Aug 2017 23:13:07 +1000
Benjamin Herrenschmidt [off-list ref] wrote:

quoted

On Mon, 2017-08-14 at 22:49 +1000, Michael Ellerman wrote:

quoted

quoted

-     /*
-      * 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).

Is there any allocation not covered by RTAS_INSTANTIATE_MAX?

Not sure, we have to audit. Talking about all this with mpe today, I
think we just need to make sure that anything that has a restriction
uses a specific identifier for *that* restriction rather than just
blindly "rma". For example, seg0_limit for segment 0 in HPT. In the
case of PACAs, we would create a specific limit that is
min(seg0_limit,rma) for pseries and -1 for powernv. etc..

The RMA limit can then become either strictly a pseries thing, or be
initialized to -1 on powernv (or max mem).

Ben.