[RFC PATCH 01/15] arch: x86: remove MAX_ORDER exceeding SECTION_SIZE check for 32bit vdso.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

For x86_64, 32bit vdso is compiled for compatibility reason and 32bit
SECTION_SIZE_BITS value is used during compilation. It causes
compilation time error when MAX_ORDER is increased in the 64bit
environment even if it is OK for 64bit SECTION_SIZE_BITS. Remove the
check during 32bit vdso compilation. The check still exists during the
compilation of other kernel components.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
 arch/x86/entry/vdso/Makefile | 1 +
 include/linux/mmzone.h       | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 05c4abc2fdfd..cad339136ed1 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -156,6 +156,7 @@ KBUILD_CFLAGS_32 += -fno-stack-protector
 KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
 KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
 KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
+KBUILD_CFLAGS_32 += -DNO_MAX_ORDER_CHECK
 
 ifdef CONFIG_RETPOLINE
 ifneq ($(RETPOLINE_VDSO_CFLAGS),)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 6a1d79d84675..c1d914a72489 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1245,9 +1245,12 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
 #define SECTION_BLOCKFLAGS_BITS \
 	((1UL << (PFN_SECTION_SHIFT - pageblock_order)) * NR_PAGEBLOCK_BITS)
 
+/* NO_MAX_ORDER_CHECK when compiling x64 32bit VDSO for 64bit system */
+#ifndef NO_MAX_ORDER_CHECK
 #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS
 #error Allocator MAX_ORDER exceeds SECTION_SIZE
 #endif
+#endif /* NO_MAX_ORDER_CHECK */
 
 static inline unsigned long pfn_to_section_nr(unsigned long pfn)
 {
-- 
2.30.2