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Message-ID: <20250822020727.202749-1-harry.yoo@oracle.com>
Date: Fri, 22 Aug 2025 11:07:27 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: harry.yoo@...cle.com
Cc: Liam.Howlett@...cle.com, akpm@...ux-foundation.org, andreyknvl@...il.com,
aneesh.kumar@...ux.ibm.com, anshuman.khandual@....com,
apopple@...dia.com, ardb@...nel.org, arnd@...db.de, bp@...en8.de,
cl@...two.org, dave.hansen@...ux.intel.com, david@...hat.com,
dennis@...nel.org, dev.jain@....com, dvyukov@...gle.com,
glider@...gle.com, gwan-gyeong.mun@...el.com, hpa@...cr.com,
jane.chu@...cle.com, jgross@...e.de, jhubbard@...dia.com,
joao.m.martins@...cle.com, joro@...tes.org, kas@...nel.org,
kevin.brodsky@....com, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
lorenzo.stoakes@...cle.com, luto@...nel.org, maobibo@...ngson.cn,
mhocko@...e.com, mingo@...hat.com, osalvador@...e.de,
peterx@...hat.com, peterz@...radead.org, rppt@...nel.org,
ryabinin.a.a@...il.com, ryan.roberts@....com, stable@...r.kernel.org,
surenb@...gle.com, tglx@...utronix.de, thuth@...hat.com, tj@...nel.org,
urezki@...il.com, vbabka@...e.cz, vincenzo.frascino@....com,
x86@...nel.org, zhengqi.arch@...edance.com,
kernel test robot <lkp@...el.com>,
Stephen Rothwell <sfr@...b.auug.org.au>
Subject: [PATCH v3] mm: fix KASAN build error due to p*d_populate_kernel()
Address a linker error introduced by a patch currently in mm-hotfixes:
"mm: introduce and use {pgd,p4d}_populate_kernel" [1].
KASAN unconditionally references kasan_early_shadow_{p4d,pud}.
However, these global variables may not exist depending on the number of
page table levels. For example, if CONFIG_PGTABLE_LEVELS=3, both
variables do not exist. Although KASAN may refernce non-existent
variables, it didn't break builds because calls to {pgd,p4d}_populate()
are optimized away at compile time.
However, {pgd,p4d}_populate_kernel() is defined as a function regardless
of the number of page table levels, so the compiler may not optimize
them away. In this case, the following linker error occurs:
ld.lld: error: undefined symbol: kasan_early_shadow_p4d
>>> referenced by init.c:260 (/home/hyeyoo/mm-new/mm/kasan/init.c:260)
>>> mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> referenced by init.c:260 (/home/hyeyoo/mm-new/mm/kasan/init.c:260)
>>> mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> did you mean: kasan_early_shadow_pmd
>>> defined in: vmlinux.a(mm/kasan/init.o)
ld.lld: error: undefined symbol: kasan_early_shadow_pud
>>> referenced by init.c:263 (/home/hyeyoo/mm-new/mm/kasan/init.c:263)
>>> mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> referenced by init.c:263 (/home/hyeyoo/mm-new/mm/kasan/init.c:263)
>>> mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> referenced by init.c:200 (/home/hyeyoo/mm-new/mm/kasan/init.c:200)
>>> mm/kasan/init.o:(zero_p4d_populate) in archive vmlinux.a
>>> referenced 1 more times
Therefore, to allow calls to {pgd,p4d}_populate_kernel() to be optimized
out at compile time, define {pgd,p4d}_populate_kernel() as macros.
This way, when pgd_populate() or p4d_populate() are simply empty macros,
the corresponding *_populate_kernel() functions can also be optimized
away.
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202508181636.0Rtk0T7x-lkp@intel.com
Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
Closes: https://lore.kernel.org/lkml/20250821160515.611d191e@canb.auug.org.au
Link: https://lore.kernel.org/linux-mm/20250818020206.4517-3-harry.yoo@oracle.com [1]
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Signed-off-by: Harry Yoo <harry.yoo@...cle.com>
---
This is intended to be fold-merged into the patch
"mm: introduce and use {pgd,p4d}_populate_kernel".
v2 -> v3:
- Explained that this fixes a linker error of a patch in mm-hotfixes.
- Added links to error reports (Closes:) and Reported-by:
include/linux/pgalloc.h | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)
diff --git a/include/linux/pgalloc.h b/include/linux/pgalloc.h
index 290ab864320f..9174fa59bbc5 100644
--- a/include/linux/pgalloc.h
+++ b/include/linux/pgalloc.h
@@ -5,20 +5,25 @@
#include <linux/pgtable.h>
#include <asm/pgalloc.h>
-static inline void pgd_populate_kernel(unsigned long addr, pgd_t *pgd,
- p4d_t *p4d)
-{
- pgd_populate(&init_mm, pgd, p4d);
- if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED)
- arch_sync_kernel_mappings(addr, addr);
-}
+/*
+ * {pgd,p4d}_populate_kernel() are defined as macros to allow
+ * compile-time optimization based on the configured page table levels.
+ * Without this, linking may fail because callers (e.g., KASAN) may rely
+ * on calls to these functions being optimized away when passing symbols
+ * that exist only for certain page table levels.
+ */
+#define pgd_populate_kernel(addr, pgd, p4d) \
+ do { \
+ pgd_populate(&init_mm, pgd, p4d); \
+ if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED) \
+ arch_sync_kernel_mappings(addr, addr); \
+ } while (0)
-static inline void p4d_populate_kernel(unsigned long addr, p4d_t *p4d,
- pud_t *pud)
-{
- p4d_populate(&init_mm, p4d, pud);
- if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_P4D_MODIFIED)
- arch_sync_kernel_mappings(addr, addr);
-}
+#define p4d_populate_kernel(addr, p4d, pud) \
+ do { \
+ p4d_populate(&init_mm, p4d, pud); \
+ if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_P4D_MODIFIED) \
+ arch_sync_kernel_mappings(addr, addr); \
+ } while (0)
#endif /* _LINUX_PGALLOC_H */
--
2.43.0
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