cma: enforce non-zero pageblock_order during cma_init_reserved_mem()

cma: enforce non-zero pageblock_order during cma_init_reserved_mem()

cma_init_reserved_mem() checks base and size alignment with
CMA_MIN_ALIGNMENT_BYTES.  However, some users might call this during early
boot when pageblock_order is 0.  That means if base and size does not have
pageblock_order alignment, it can cause functional failures during cma
activate area.

So let's enforce pageblock_order to be non-zero during
cma_init_reserved_mem() to catch such wrong usages.

1. This was seen with fadump on PowerPC which was calling
   cma_init_reserved_mem() before the pageblock_order was initialized.
   This is now fixed in the fadump on PowerPC itself.  The details of that
   can be found in the patch including the userspace-visible effect of the
   issue [1].

2. However it was also decided that we should add a stronger
   enforcement check within cma_init_reserved_mem() to catch such wrong
   usages [2].  Hence this patch.  This is ok to be in -next and there is
   no "Fixes" tag required for this patch.

[1]: https://lore.kernel.org/all/3ae208e48c0d9cefe53d2dc4f593388067405b7d.1729146153.git.ritesh.list@gmail.com/
[2]: https://lore.kernel.org/all/83eb128e-4f06-4725-a843-a4563f246a44@redhat.com/

Link: https://lkml.kernel.org/r/e274344b44d5f80fa54c52f530387257fe99ec65.1731505681.git.ritesh.list@gmail.com
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>