Re: [PATCH RFC 3/3] powerpc/64: Enable use of radix MMU under hypervisor on POWER9

[Paul Mackerras <paulus@ozlabs.org>]

On Mon, Dec 05, 2016 at 07:55:32PM +1100, Benjamin Herrenschmidt wrote:
> On Mon, 2016-12-05 at 19:04 +1100, Paul Mackerras wrote:
> > +       vec5 = of_get_flat_dt_prop(chosen, "ibm,architecture-vec-5", &size);
> > +       if (!vec5 || size <= OV5_INDX(OV5_MMU_RADIX_300))
> > +               return;
> 
> Could be bike shedding but shouldn't we first check if
> we are in an LPAR and bail out of we are not, then
> if we *are* and the above size is too small to contain
> the ARCH 3.00 options, also disable radix as obviously
> the hypervisor doesn't know about it ?

This is *very* early on, so early that we haven't yet decided what
platform we're on.  If we're not in an LPAR then we won't have a
/chosen/ibm-architecture-vec-5 property.  Any hypervisor that is too
old to have that property will also be too old to set the radix
bit in the ibm,pa-features property, so we won't use radix.

If we do have the property but it's short then yes that's a good
indication that the hypervisor can't do radix, though in that case
it's strange that it set the radix bit in the ibm,pa-features property
(which must have been set otherwise we wouldn't have got here).

I'll do a new patch.

> > +       if (!(vec5[OV5_INDX(OV5_MMU_RADIX_300)] & OV5_FEAT(OV5_MMU_RADIX_300)))
> > +               /* Hypervisor doesn't support radix */
> > +               cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
> > +}
> > +

Paul.