From: Mike Rapoport (Microsoft) <rppt@kernel.org>
Date: Wed, 11 Feb 2026 10:31:38 +0000 (+0200)
Subject: mm: don't special case !MMU for is_zero_pfn() and my_zero_pfn()
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=652d12bc74a075f345f228f8945e05517a38874d;p=thirdparty%2Fkernel%2Flinux.git

mm: don't special case !MMU for is_zero_pfn() and my_zero_pfn()

Patch series "arch, mm: consolidate empty_zero_page", v3.

These patches cleanup handling of ZERO_PAGE() and zero_pfn.


This patch (of 4):

nommu architectures have empty_zero_page and define ZERO_PAGE() and
although they don't really use it to populate page tables, there is no
reason to hardwire !MMU implementation of is_zero_pfn() and my_zero_pfn()
to 0.

Drop #ifdef CONFIG_MMU around implementations of is_zero_pfn() and
my_zero_pfn() and remove !MMU version.

While on it, make zero_pfn __ro_after_init.

Link: https://lkml.kernel.org/r/20260211103141.3215197-1-rppt@kernel.org
Link: https://lkml.kernel.org/r/20260211103141.3215197-2-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guo Ren <guoren@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Magnus Lindholm <linmag7@gmail.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index a50df42a893fb..5e772599d9a5c 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1917,7 +1917,6 @@ static inline void pfnmap_setup_cachemode_pfn(unsigned long pfn, pgprot_t *prot)
 	pfnmap_setup_cachemode(pfn, PAGE_SIZE, prot);
 }
 
-#ifdef CONFIG_MMU
 #ifdef __HAVE_COLOR_ZERO_PAGE
 static inline int is_zero_pfn(unsigned long pfn)
 {
@@ -1940,18 +1939,7 @@ static inline unsigned long my_zero_pfn(unsigned long addr)
 	extern unsigned long zero_pfn;
 	return zero_pfn;
 }
-#endif
-#else
-static inline int is_zero_pfn(unsigned long pfn)
-{
-	return 0;
-}
-
-static inline unsigned long my_zero_pfn(unsigned long addr)
-{
-	return 0;
-}
-#endif /* CONFIG_MMU */
+#endif /* __HAVE_COLOR_ZERO_PAGE */
 
 #ifdef CONFIG_MMU
 
diff --git a/mm/memory.c b/mm/memory.c
index 7084c426f9338..6b504fc5e815f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -162,21 +162,8 @@ static int __init disable_randmaps(char *s)
 }
 __setup("norandmaps", disable_randmaps);
 
-unsigned long zero_pfn __read_mostly;
-EXPORT_SYMBOL(zero_pfn);
-
 unsigned long highest_memmap_pfn __read_mostly;
 
-/*
- * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init()
- */
-static int __init init_zero_pfn(void)
-{
-	zero_pfn = page_to_pfn(ZERO_PAGE(0));
-	return 0;
-}
-early_initcall(init_zero_pfn);
-
 void mm_trace_rss_stat(struct mm_struct *mm, int member)
 {
 	trace_rss_stat(mm, member);
diff --git a/mm/mm_init.c b/mm/mm_init.c
index df34797691bda..f3755a66b9d0f 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -53,6 +53,9 @@ EXPORT_SYMBOL(mem_map);
 void *high_memory;
 EXPORT_SYMBOL(high_memory);
 
+unsigned long zero_pfn __ro_after_init;
+EXPORT_SYMBOL(zero_pfn);
+
 #ifdef CONFIG_DEBUG_MEMORY_INIT
 int __meminitdata mminit_loglevel;
 
@@ -2672,6 +2675,13 @@ static void __init mem_init_print_info(void)
 		);
 }
 
+static int __init init_zero_pfn(void)
+{
+	zero_pfn = page_to_pfn(ZERO_PAGE(0));
+	return 0;
+}
+early_initcall(init_zero_pfn);
+
 void __init __weak arch_mm_preinit(void)
 {
 }