mm: rename my_zero_pfn() to zero_pfn()

my_zero_pfn() is a silly name.

Rename zero_pfn variable to zero_page_pfn and my_zero_pfn() function to
zero_pfn().

While on it, move extern declarations of zero_page_pfn outside the
functions that use it and add a comment about what ZERO_PAGE is.

Link: https://lkml.kernel.org/r/20260211103141.3215197-3-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-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: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.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: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/x86/kvm/mmu/spte.h

@@ -248,7 +248,7 @@ extern u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
 
 static inline hpa_t kvm_mmu_get_dummy_root(void)
 {
-	return my_zero_pfn(0) << PAGE_SHIFT;
+	return zero_pfn(0) << PAGE_SHIFT;
 }
 
 static inline bool kvm_mmu_is_dummy_root(hpa_t shadow_page)

fs/dax.c

@@ -1360,7 +1360,7 @@ static vm_fault_t dax_load_hole(struct xa_state *xas, struct vm_fault *vmf,
 {
 	struct inode *inode = iter->inode;
 	unsigned long vaddr = vmf->address;
-	unsigned long pfn = my_zero_pfn(vaddr);
+	unsigned long pfn = zero_pfn(vaddr);
 	vm_fault_t ret;
 
 	*entry = dax_insert_entry(xas, vmf, iter, *entry, pfn, DAX_ZERO_PAGE);

fs/proc/vmcore.c

@@ -525,7 +525,7 @@ static int remap_oldmem_pfn_checked(struct vm_area_struct *vma,
 {
 	unsigned long map_size;
 	unsigned long pos_start, pos_end, pos;
-	unsigned long zeropage_pfn = my_zero_pfn(0);
+	unsigned long zeropage_pfn = zero_pfn(0);
 	size_t len = 0;
 
 	pos_start = pfn;

include/linux/pgtable.h

@@ -1917,27 +1917,39 @@ static inline void pfnmap_setup_cachemode_pfn(unsigned long pfn, pgprot_t *prot)
 	pfnmap_setup_cachemode(pfn, PAGE_SIZE, prot);
 }
 
+/*
+ * ZERO_PAGE() is global shared page(s) that is always zero. It is used for
+ * zero-mapped memory areas, CoW etc.
+ *
+ * On architectures that __HAVE_COLOR_ZERO_PAGE there are several such pages
+ * for different ranges in the virtual address space.
+ *
+ * zero_page_pfn identifies the first (or the only) pfn for these pages.
+ */
 #ifdef __HAVE_COLOR_ZERO_PAGE
 static inline int is_zero_pfn(unsigned long pfn)
 {
-	extern unsigned long zero_pfn;
-	unsigned long offset_from_zero_pfn = pfn - zero_pfn;
+	extern unsigned long zero_page_pfn;
+	unsigned long offset_from_zero_pfn = pfn - zero_page_pfn;
+
 	return offset_from_zero_pfn <= (zero_page_mask >> PAGE_SHIFT);
 }
 
-#define my_zero_pfn(addr)	page_to_pfn(ZERO_PAGE(addr))
+#define zero_pfn(addr)	page_to_pfn(ZERO_PAGE(addr))
 
 #else
 static inline int is_zero_pfn(unsigned long pfn)
 {
-	extern unsigned long zero_pfn;
-	return pfn == zero_pfn;
+	extern unsigned long zero_page_pfn;
+
+	return pfn == zero_page_pfn;
 }
 
-static inline unsigned long my_zero_pfn(unsigned long addr)
+static inline unsigned long zero_pfn(unsigned long addr)
 {
-	extern unsigned long zero_pfn;
-	return zero_pfn;
+	extern unsigned long zero_page_pfn;
+
+	return zero_page_pfn;
 }
 #endif /* __HAVE_COLOR_ZERO_PAGE */
 

mm/huge_memory.c

@@ -2972,7 +2972,7 @@ static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
 	for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
 		pte_t entry;
 
-		entry = pfn_pte(my_zero_pfn(addr), vma->vm_page_prot);
+		entry = pfn_pte(zero_pfn(addr), vma->vm_page_prot);
 		entry = pte_mkspecial(entry);
 		if (pmd_uffd_wp(old_pmd))
 			entry = pte_mkuffd_wp(entry);

mm/memory.c

@@ -5224,7 +5224,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	/* Use the zero-page for reads */
 	if (!(vmf->flags & FAULT_FLAG_WRITE) &&
 			!mm_forbids_zeropage(vma->vm_mm)) {
-		entry = pte_mkspecial(pfn_pte(my_zero_pfn(vmf->address),
+		entry = pte_mkspecial(pfn_pte(zero_pfn(vmf->address),
 						vma->vm_page_prot));
 		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
 				vmf->address, &vmf->ptl);

mm/migrate.c

@@ -321,7 +321,7 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
 	if (!pages_identical(page, ZERO_PAGE(0)))
 		return false;
 
-	newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address),
+	newpte = pte_mkspecial(pfn_pte(zero_pfn(pvmw->address),
 					pvmw->vma->vm_page_prot));
 
 	if (pte_swp_soft_dirty(old_pte))

mm/mm_init.c

@@ -53,8 +53,8 @@ EXPORT_SYMBOL(mem_map);
 void *high_memory;
 EXPORT_SYMBOL(high_memory);
 
-unsigned long zero_pfn __ro_after_init;
-EXPORT_SYMBOL(zero_pfn);
+unsigned long zero_page_pfn __ro_after_init;
+EXPORT_SYMBOL(zero_page_pfn);
 
 #ifdef CONFIG_DEBUG_MEMORY_INIT
 int __meminitdata mminit_loglevel;
@@ -2675,12 +2675,12 @@ static void __init mem_init_print_info(void)
 		);
 }
 
-static int __init init_zero_pfn(void)
+static int __init init_zero_page_pfn(void)
 {
-	zero_pfn = page_to_pfn(ZERO_PAGE(0));
+	zero_page_pfn = page_to_pfn(ZERO_PAGE(0));
 	return 0;
 }
-early_initcall(init_zero_pfn);
+early_initcall(init_zero_page_pfn);
 
 void __init __weak arch_mm_preinit(void)
 {

mm/userfaultfd.c

@@ -357,7 +357,7 @@ static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
 	if (mm_forbids_zeropage(dst_vma->vm_mm))
 		return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr);
 
-	_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
+	_dst_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr),
 					 dst_vma->vm_page_prot));
 	ret = -EAGAIN;
 	dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
@@ -1229,7 +1229,7 @@ static int move_zeropage_pte(struct mm_struct *mm,
 		return -EAGAIN;
 	}
 
-	zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
+	zero_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr),
 					 dst_vma->vm_page_prot));
 	ptep_clear_flush(src_vma, src_addr, src_pte);
 	set_pte_at(mm, dst_addr, dst_pte, zero_pte);