remap_pfn_range(9)

💅 remap_pfn_range — like, the kernel-memory-to-userspace glow-up

Okay bestie, welcome to the Kernel API Manual ✨ — this one's called remap_pfn_range(9) and it's literally the function that hands kernel memory over to userspace. Main character energy fr fr 🫶

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🌸 NAME

remap_pfn_range — remap kernel memory to userspace 💫

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✨ SYNOPSIS

int remap_pfn_range (struct vm_area_struct *vma , unsigned long addr ,
       unsigned long pfn , unsigned long size , pgprot_t prot );

That's the whole vibe check right there 👆 five args, no notes.

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🎀 ARGUMENTS

• vma — the user vma you're mapping into, i.e. the userspace side of the situationship 🦋
• addr — the target, page-aligned user address where the mapping starts. Page-aligned, bestie, don't play with me 🙈
• pfn — page frame number of the kernel physical memory address 👑
• size — how big the mapping area is 🌈
• prot — page protection flags for this mapping, aka the outfit it wears 💅

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💀 NOTE

This is only safe if the mm semaphore is held when it's called. Not "probably fine", not "we'll see" — held. Do not come for me if you skip this, I warned you 😭

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⭐ RETURN

• 0 on success 🎉
• a negative error code otherwise 💔

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🔥 SEE ALSO

Kernel file ./mm/memory.c — and honestly the whole extended friend group:

• free_pgd_range(9)
• free_pgtables(9)
• __vm_normal_page(9)
• vm_normal_page(9)
• vm_normal_folio(9)
• vm_normal_page_pmd(9)
• vm_normal_folio_pmd(9)
• vm_normal_page_pud(9)
• restore_exclusive_pte(9)
• cond_install_uffd_wp_ptes(9)
• zap_vma_for_reaping(9)
• unmap_vmas(9)
• zap_vma_range_batched(9)
• zap_vma_range(9)
• zap_special_vma_range(9)
• vm_insert_pages(9)
• vm_insert_page(9)
• vm_map_pages(9)
• vm_map_pages_zero(9)
• vmf_insert_pfn_prot(9)
• vmf_insert_pfn(9)
• vm_iomap_memory(9)
• __vmf_anon_prepare(9)
• finish_mkwrite_fault(9)
• unmap_mapping_folio(9)
• unmap_mapping_pages(9)
• unmap_mapping_range(9)
• set_pte_range(9)
• finish_fault(9)
• mm_account_fault(9)
• follow_pfnmap_start(9)
• follow_pfnmap_end(9)
• generic_access_phys(9)
• access_remote_vm(9)
• copy_remote_vm_str(9)
• folio_zero_user(9)

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okayyy that's the whole page, you ate that 💖 This one ships out of ./mm and is dated October 2026 — so go forth, remap responsibly, and keep that mm semaphore held, iykyk 🧚🍓