__vmf_anon_prepare(9)

📦 version 7.3.1, in nixpkgs unstable

💖 __vmf_anon_prepare — like, the Kernel API Manual page, bestie ✨

okay so we're in the <pink>Kernel API Manual</pink> today and the star of the show is __vmf_anon_prepare(9) 🎀 buckle up.

🌸 NAME 🌸

__vmf_anon_prepare — literally just Prepare to handle an anonymous fault. that's the whole vibe 🫶

✨ SYNOPSIS ✨

vm_fault_t __vmf_anon_prepare (struct vm_fault *vmf );

like yes, that's it, that's the signature 💅

🦋 ARGUMENTS 🦋

  • vmf — the vm_fault descriptor that got handed to you straight from the fault handler. it's giving "here u go, do something with this" 🎁

💜 DESCRIPTION 💜

okay so picture this: you're in a fault handler and you're about to insert an anonymous page into a VMA. the move here is to call this function — __vmf_anon_prepare — and not anon_vma_prepare. lowkey important distinction, iykyk 👑

now here's the part where you gotta pay attention 🙈 if this VMA doesn't already have an associated anon_vma, and you're only protected by the per-VMA lock, then the caller must retry with the mmap_lock held. no cap, that's a requirement.

why?? because __anon_vma_prepare is gonna go look at adjacent VMAs to figure out whether this VMA can share its anon_vma, and that is not safe to do when all you're holding is the per-VMA lock for this VMA. 💀 like genuinely not safe. so don't.

🍓 RETURN 🍓

  • 0 — slay, fault handling can proceed ✨
  • any other value — should be returned to the caller. that's it, hand it back 🫶

🌈 SEE ALSO 🌈

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

and that's the page!! 💖✨ this little baby lives in ./mm and the version is dated October 2026, filed under __vmf_anon_prepare(9) — mwah, go forth and prepare those anon VMAs correctly bestie 🧚‍♀️💅👑

📦 where this page comes from