[PATCH -next v2] arm64: fix build warning for ARM64_MEMSTART_SHIFT

[Zhang Jianhua]

When building with W=1, the following warning occurs.

arch/arm64/include/asm/kernel-pgtable.h:129:41: error: "PUD_SHIFT" is not defined, evaluates to 0 [-Werror=undef]
  129 | #define ARM64_MEMSTART_SHIFT            PUD_SHIFT
      |                                         ^~~~~~~~~
arch/arm64/include/asm/kernel-pgtable.h:142:5: note: in expansion of macro ‘ARM64_MEMSTART_SHIFT’
  142 | #if ARM64_MEMSTART_SHIFT < SECTION_SIZE_BITS
      |     ^~~~~~~~~~~~~~~~~~~~

The reason is that PUD_SHIFT isn't defined if CONFIG_PGTABLE_LEVELS == 3
and CONFIG_VA_BITS == 39. For this scenario, the macro ARM64_MEMSTART_SHIFT
would be defined to different value of PUD_SHIFT/CONT_PMD_SHIFT/CONT_PMD_SHIFT
according to different config, any of them would be undefined as long as
the value is equal to PGDIR_SHIFT, so add judgement before reference and
set the default value.

Signed-off-by: Zhang Jianhua <chris.zjh@xxxxxxxxxx>
---
v2:
	Add define judgement of PUD_SHIFT/CONT_PMD_SHIFT/CONT_PMD_SHIFT before
	use them, instead of define PUD_SHIFT only.
---
---
 arch/arm64/include/asm/kernel-pgtable.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
index 577773870b66..51bdce66885d 100644
--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -125,12 +125,14 @@
  * (64k granule), or a multiple that can be mapped using contiguous bits
  * in the page tables: 32 * PMD_SIZE (16k granule)
  */
-#if defined(CONFIG_ARM64_4K_PAGES)
+#if defined(CONFIG_ARM64_4K_PAGES) && defined(PUD_SHIFT)
 #define ARM64_MEMSTART_SHIFT		PUD_SHIFT
-#elif defined(CONFIG_ARM64_16K_PAGES)
+#elif defined(CONFIG_ARM64_16K_PAGES) && defined(CONT_PMD_SHIFT)
 #define ARM64_MEMSTART_SHIFT		CONT_PMD_SHIFT
-#else
+#elif defined(CONFIG_ARM64_64K_PAGES) && defined(PMD_SHIFT)
 #define ARM64_MEMSTART_SHIFT		PMD_SHIFT
+#else
+#define ARM64_MEMSTART_SHIFT		PGDIR_SHIFT
 #endif
 
 /*
-- 
2.34.1