Re: [PATCH v3 2/4] mm: rename my_zero_pfn() to zero_pfn()

Liam R. Howlett
2026-02-12T18:34:45Z

* Mike Rapoport <rppt@kernel.org> [260211 05:32]:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>
> 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.
>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
> arch/x86/kvm/mmu/spte.h | 2 +-
> fs/dax.c | 2 +-
> fs/proc/vmcore.c | 2 +-
> include/linux/pgtable.h | 28 ++++++++++++++++++++--------
> mm/huge_memory.c | 2 +-
> mm/memory.c | 2 +-
> mm/migrate.c | 2 +-
> mm/mm_init.c | 10 +++++-----
> mm/userfaultfd.c | 4 ++--
> 9 files changed, 33 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index 91ce29fd6f1b..8c0ffa2cded6 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/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)
> diff --git a/fs/dax.c b/fs/dax.c
> index 289e6254aa30..b78cff9c91b3 100644
> --- a/fs/dax.c
> +++ b/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);
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index f188bd900eb2..44d15436439f 100644
> --- a/fs/proc/vmcore.c
> +++ b/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;
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 08a88b0d56e5..9bacf4df9769 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1882,27 +1882,39 @@ 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 */
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 44ff8a648afd..bc15fd152526 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2968,7 +2968,7 @@ 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);
> diff --git a/mm/memory.c b/mm/memory.c
> index 51d2018a387a..ae610afa9cea 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5165,7 +5165,7 @@ 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);
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 1bf2cf8c44dd..739c4e03769b 100644
> --- a/mm/migrate.c
> +++ b/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))
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index dcf9eff34f83..a0ca236eb4f5 100644
> --- a/mm/mm_init.c
> +++ b/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;
> @@ -2670,12 +2670,12 @@ 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)
> {
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 927086bb4a3c..e19872e51878 100644
> --- a/mm/userfaultfd.c
> +++ b/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);
> --
> 2.51.0
>