kmap_local_page(9)

🌸 kmap_local_page — Kernel API Manual, section 9 🌸

okay so bestie, welcome to kmap_local_page(9), straight out of the Kernel API Manual. this is the page about mapping a page for temporary usage, and honestly? it's giving "small function, big rules" energy. let's get into it 💅

---

✨ NAME ✨

kmap_local_page — map a page for temporary usage 🗺️

---

🎀 SYNOPSIS 🎀

void * kmap_local_page (const struct page *page );

---

🦋 ARGUMENTS 🦋

• page — pointer to the page to be mapped. that's it, that's the whole argument, she's lowkey simple like that 🫶

---

⭐ RETURN ⭐

the virtual address of the mapping. slay, that's what you get back ✨

---

💖 DESCRIPTION 💖

okay so here's the tea. you can invoke this from any context, including interrupts. any context, bestie, no cap 🫶

but — and this is the important part — it requires careful handling when nesting multiple mappings, because the map management is stack based. the unmap has to happen in the reverse order of the map operation:

addr1 = kmap_local_page(page1); addr2 = kmap_local_page(page2); ...
kunmap_local(addr2); kunmap_local(addr1);

⚠️ unmapping addr1 before addr2 is invalid and causes malfunction. not a vibe. do not do this. 💀

contrary to kmap mappings, the mapping is only valid in the context of the caller and cannot be handed to other contexts. it's main character energy: it stays in its own lane 🙈

on CONFIG_HIGHMEM=n kernels and for low memory pages, this returns the virtual address of the direct mapping. only real highmem pages are temporarily mapped 🔥

while kmap_local_page is significantly faster than kmap for the highmem case, it comes with restrictions about the pointer validity. fast, yes. free, no. the tradeoff is real 😭

on HIGHMEM enabled systems, mapping a highmem page has the side effect of disabling migration in order to keep the virtual address stable across preemption. and listen — no caller of kmap_local_page can rely on this side effect. it's a side effect, not a promise, bestie, don't build your whole personality on it 💅

---

🌈 SEE ALSO 🌈

kernel file ./include/linux/highmem.h, plus this whole iconic friend group:

• kmap(9)
• kunmap(9)
• kmap_to_page(9)
• kmap_flush_unused(9)
• kmap_local_folio(9)
• kmap_atomic(9)
• clear_user_page(9)
• clear_user_pages(9)
• clear_user_highpage(9)
• clear_user_highpages(9)
• vma_alloc_zeroed_movable_folio(9)
• memcpy_from_folio(9)
• memcpy_to_folio(9)
• folio_zero_tail(9)
• folio_fill_tail(9)
• memcpy_from_file_folio(9)
• folio_zero_segments(9)
• folio_zero_segment(9)
• folio_zero_range(9)
• folio_release_kmap(9)

---

and that's the whole page, bestie 🧚💜 this one lives in ./include/linux, dated October 2026, and it's filed under kmap_local_page(9). go forth and unmap in reverse order, i'm begging you 🙏🍓