+ mm-introduce-and-use-pgdp4d_populate_kernel-fix.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: fix KASAN build error due to p*d_populate_kernel()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-introduce-and-use-pgdp4d_populate_kernel-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-introduce-and-use-pgdp4d_populate_kernel-fix.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Harry Yoo <harry.yoo@oracle.com>
Subject: mm: fix KASAN build error due to p*d_populate_kernel()
Date: Thu, 21 Aug 2025 18:35:42 +0900

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.

Link: https://lkml.kernel.org/r/20250821093542.37844-1-harry.yoo@oracle.com
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/pgalloc.h |   26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

--- a/include/linux/pgalloc.h~mm-introduce-and-use-pgdp4d_populate_kernel-fix
+++ a/include/linux/pgalloc.h
@@ -5,20 +5,18 @@
 #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);
-}
+#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 */
_

Patches currently in -mm which might be from harry.yoo@oracle.com are

mm-move-page-table-sync-declarations-to-linux-pgtableh.patch
mm-introduce-and-use-pgdp4d_populate_kernel.patch
mm-introduce-and-use-pgdp4d_populate_kernel-fix.patch
x86-mm-64-define-arch_page_table_sync_mask-and-arch_sync_kernel_mappings.patch