Use of THP requires that the VMA containing the guest memory is
2MB aligned. Unfortunately, nothing in kvmtool ensures that the
memory is actually aligned, making the use of THP very unlikely.

Just follow what we're already doing for virtio, and expand our
forced alignment to 2M.

* without this patch:
root@muffin-man:~# for i in $(seq 1 5); do ./hackbench 50 process 1000; done
Running with 50*40 (== 2000) tasks.
Time: 113.600
Running with 50*40 (== 2000) tasks.
Time: 108.650
Running with 50*40 (== 2000) tasks.
Time: 110.753
Running with 50*40 (== 2000) tasks.
Time: 116.992
Running with 50*40 (== 2000) tasks.
Time: 117.317

* with this patch:
root@muffin-man:~# for i in $(seq 1 5); do ./hackbench 50 process 1000; done
Running with 50*40 (== 2000) tasks.
Time: 97.613
Running with 50*40 (== 2000) tasks.
Time: 96.111
Running with 50*40 (== 2000) tasks.
Time: 97.090
Running with 50*40 (== 2000) tasks.
Time: 100.820
Running with 50*40 (== 2000) tasks.
Time: 100.298

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>