On Fri, Aug 14, 2015 at 02:15:23PM +0200, Ard Biesheuvel wrote:

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On 7 aug. 2015, at 21:01, Stuart Yoder [off-list ref] wrote:

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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