[RFC] arm64: defconfig: enable 48-bit VA by default

[Catalin Marinas]

On Fri, Aug 14, 2015 at 02:15:23PM +0200, Ard Biesheuvel wrote:
> >> On 7 aug. 2015, at 21:01, Stuart Yoder <stuart.yoder at freescale.com> wrote:
> >>
> >> >> Whether defconfig supports your platform optimally has nothing to do
> >> >> with that. Of course, we should deal with the unexpected memory layout
> >> >> gracefully, which is why Mark Rutland and myself proposed patches to
> >> >> fix the panic you reported. But in a development context, I think it
> >> >> is perfectly acceptable to simply load the kernel at 0x80_8000_0000,
> >> >> and be able to run defconfig fine while losing just 2 GB of your 16 GB
> >> >> at the low end.
[...]
> So we still need to decide how to fix the case where the linear region
> is not of sufficient size to cover all of memory, considering that is
> what got this discussion started in the first place.

We already have a solution, just enable 4-levels of page tables (only
that I don't think we should change defconfig as well).

If we want to do any tricks like compacting the memory range, it needs
to be backed by benchmarks to prove that it's worth compared to a full
48-bit VA.

-- 
Catalin