On Thu, 28 Oct 2021 14:59:15 +0200, Christophe Leroy wrote:

When ARCH_SUPPORTS_DEBUG_PAGEALLOC is not selected, the user can
still select CONFIG_DEBUG_PAGEALLOC in which case __kernel_map_pages()
is provided by mm/page_poison.c

So only define __kernel_map_pages() when both
CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC and CONFIG_DEBUG_PAGEALLOC
are defined.

[...]

Applied to powerpc/next.

[1/1] powerpc: Don't provide __kernel_map_pages() without ARCH_SUPPORTS_DEBUG_PAGEALLOC
      https://git.kernel.org/powerpc/c/f8c0e36b48e32b14bb83332d24e0646acd31d9e9

cheers