arm64: pageattr: Explicitly bail out when changing permissions for vmalloc_huge mappings

arm64: pageattr: Explicitly bail out when changing permissions for vmalloc_huge mappings

arm64 uses apply_to_page_range to change permissions for kernel vmalloc mappings,
which does not support changing permissions for block mappings. This function
will change permissions until it encounters a block mapping, and will bail
out with a warning. Since there are no reports of this triggering, it
implies that there are currently no cases of code doing a vmalloc_huge()
followed by partial permission change. But this is a footgun waiting to
go off, so let's detect it early and avoid the possibility of permissions
in an intermediate state. So,  explicitly disallow changing permissions
for VM_ALLOW_HUGE_VMAP mappings.

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20250403052844.61818-1-dev.jain@arm.com
Signed-off-by: Will Deacon <will@kernel.org>