[PATCH] powerpc/mm: Reinstate ARCH_FORCE_MAX_ORDER ranges

[Michael Ellerman <mpe@ellerman.id.au>]

Commit 1e8fed873e74 ("powerpc: drop ranges for definition of
ARCH_FORCE_MAX_ORDER") removed the limits on the possible values for
ARCH_FORCE_MAX_ORDER.

However removing the ranges entirely causes some common work flows to
break. For example building a defconfig (which uses 64K pages), changing
the page size to 4K, and rebuilding used to work, because
ARCH_FORCE_MAX_ORDER would be clamped to 12 by the ranges.

With the ranges removed it creates a kernel that builds but crashes at
boot:
  kernel BUG at mm/huge_memory.c:470!
  Oops: Exception in kernel mode, sig: 5 [#1]
  ...
  NIP hugepage_init+0x9c/0x278
  LR  do_one_initcall+0x80/0x320
  Call Trace:
    do_one_initcall+0x80/0x320
    kernel_init_freeable+0x304/0x3ac
    kernel_init+0x30/0x1a0
    ret_from_kernel_user_thread+0x14/0x1c

The reasoning for removing the ranges was that some of the values were
too large. So take that into account and limit the maximums to 10 which
is the default max, except for the 4K case which uses 12.

Fixes: 1e8fed873e74 ("powerpc: drop ranges for definition of ARCH_FORCE_MAX_ORDER")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/Kconfig | 6 ++++++
 1 file changed, 6 insertions(+)

I plan to merge this via the powerpc fixes branch.

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 539d1f03ff42..bff5820b7cda 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -906,11 +906,17 @@ config DATA_SHIFT
 
 config ARCH_FORCE_MAX_ORDER
 	int "Order of maximal physically contiguous allocations"
+	range 7 8 if PPC64 && PPC_64K_PAGES
 	default "8" if PPC64 && PPC_64K_PAGES
+	range 12 12 if PPC64 && !PPC_64K_PAGES
 	default "12" if PPC64 && !PPC_64K_PAGES
+	range 8 10 if PPC32 && PPC_16K_PAGES
 	default "8" if PPC32 && PPC_16K_PAGES
+	range 6 10 if PPC32 && PPC_64K_PAGES
 	default "6" if PPC32 && PPC_64K_PAGES
+	range 4 10 if PPC32 && PPC_256K_PAGES
 	default "4" if PPC32 && PPC_256K_PAGES
+	range 10 10
 	default "10"
 	help
 	  The kernel page allocator limits the size of maximal physically
-- 
2.40.1