KVM: PPC: Book3S HV: Migrate pinned pages out of CMA

When PCI Device pass-through is enabled via VFIO, KVM-PPC will
pin pages using get_user_pages_fast(). One of the downsides of
the pinning is that the page could be in CMA region. The CMA
region is used for other allocations like the hash page table.
Ideally we want the pinned pages to be from non CMA region.

This patch (currently only for KVM PPC with VFIO) forcefully
migrates the pages out (huge pages are omitted for the moment).
There are more efficient ways of doing this, but that might
be elaborate and might impact a larger audience beyond just
the kvm ppc implementation.

The magic is in new_iommu_non_cma_page() which allocates the
new page from a non CMA region.

I've tested the patches lightly at my end. The full solution
requires migration of THP pages in the CMA region. That work
will be done incrementally on top of this.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[mpe: Merged via powerpc tree as that's where the changes are]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>