[PATCH] arm64: fix MAX_ORDER for 64K pagesize

[Mark Salter]

With a kernel configured with ARM64_64K_PAGES && !TRANSPARENT_HUGEPAGE
I get this at early boot:

  SMP: Total of 8 processors activated.
  devtmpfs: initialized
  Unable to handle kernel NULL pointer dereference at virtual address 00000008
  pgd = fffffe0000050000
  [00000008] *pgd=00000043fba00003, *pmd=00000043fba00003, *pte=00e0000078010407
  Internal error: Oops: 96000006 [#1] SMP
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.15.0-rc864k+ #44
  task: fffffe03bc040000 ti: fffffe03bc080000 task.ti: fffffe03bc080000
  PC is at __list_add+0x10/0xd4
  LR is at free_one_page+0x270/0x638
  ...
  Call trace:
  [<fffffe00003ee970>] __list_add+0x10/0xd4
  [<fffffe000019c478>] free_one_page+0x26c/0x638
  [<fffffe000019c8c8>] __free_pages_ok.part.52+0x84/0xbc
  [<fffffe000019d5e8>] __free_pages+0x74/0xbc
  [<fffffe0000c01350>] init_cma_reserved_pageblock+0xe8/0x104
  [<fffffe0000c24de0>] cma_init_reserved_areas+0x190/0x1e4
  [<fffffe0000090418>] do_one_initcall+0xc4/0x154
  [<fffffe0000bf0a50>] kernel_init_freeable+0x204/0x2a8
  [<fffffe00007520a0>] kernel_init+0xc/0xd4

This happens in this configuration because __free_one_page() is called
with an order greater than MAX_ORDER, accesses past zone->free_list[]
and passes a bogus list_head to list_add().

arch/arm64/Kconfig has:

  config FORCE_MAX_ZONEORDER
	int
	default "14" if (ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE)
	default "11"

So with THP turned off MAX_ORDER == 11 but init_cma_reserved_pageblock()
passes __free_pages() an order of pageblock_order which is based on
(HPAGE_SHIFT - PAGE_SHIFT) which is 13 for 64K pages. I worked around
this by removing the THP test so FORCE_MAX_ZONEORDER is always 14 for
ARM64_64K_PAGES.

Signed-off-by: Mark Salter <msalter@xxxxxxxxxx>
---
 arch/arm64/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7295419..42a334e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -269,7 +269,7 @@ config XEN
 
 config FORCE_MAX_ZONEORDER
 	int
-	default "14" if (ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE)
+	default "14" if ARM64_64K_PAGES
 	default "11"
 
 endmenu
-- 
1.9.0

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