ENUM VM_FAULT_REASON(9)

✨ enum vm_fault_reason(9) ✨

okay so bestie, welcome to the enum vm_fault_reason man page from the Kernel API Manual 💖 this is genuinely one of those pages that looks scary and then turns out to be a whole mood board of "what happened when the fault got handled" flags, and honestly? iconic.

The core lore: page fault handlers return a bitmask made of these values to tell the core VM what actually went down while handling the fault. And the core VM uses that info to decide whether a process gets delivered SIGBUS or just gets its major/minor fault counters bumped up. no cap, that's the whole drama 🎀

✨ SYNOPSIS ✨

enum vm_fault_reason {
    VM_FAULT_OOM ,
    VM_FAULT_SIGBUS ,
    VM_FAULT_MAJOR ,
    VM_FAULT_HWPOISON ,
    VM_FAULT_HWPOISON_LARGE ,
    VM_FAULT_SIGSEGV ,
    VM_FAULT_NOPAGE ,
    VM_FAULT_LOCKED ,
    VM_FAULT_RETRY ,
    VM_FAULT_FALLBACK ,
    VM_FAULT_DONE_COW ,
    VM_FAULT_NEEDDSYNC ,
    VM_FAULT_COMPLETED ,
    VM_FAULT_HINDEX_MASK

};

🌸 Constants 🌸

like, every single one, in order, no skips, we eating the whole plate 🍓

• VM_FAULT_OOM — Out Of Memory 💀
• VM_FAULT_SIGBUS — Bad access 😭
• VM_FAULT_MAJOR — Page read from storage 🦋
• VM_FAULT_HWPOISON — Hit poisoned small page 🧚
• VM_FAULT_HWPOISON_LARGE — Hit poisoned large page. Index encoded in upper bits ✨
• VM_FAULT_SIGSEGV — segmentation fault 🙈
• VM_FAULT_NOPAGE — ->fault installed the pte, not return page 💅
• VM_FAULT_LOCKED — ->fault locked the returned page 🔥
• VM_FAULT_RETRY — ->fault blocked, must retry 👑
• VM_FAULT_FALLBACK — huge page fault failed, fall back to small 🌈
• VM_FAULT_DONE_COW — ->fault has fully handled COW ⭐
• VM_FAULT_NEEDDSYNC — ->fault did not modify page tables and needs fsync to complete (for synchronous page faults in DAX) 💜
• VM_FAULT_COMPLETED — ->fault completed, meanwhile mmap lock released 🫶
• VM_FAULT_HINDEX_MASK — mask HINDEX value 💖

bestie the ->fault notation is literal, don't rename it, it's giving "pointer to the fault callback" and it's staying exactly like that 💅

🦋 SEE ALSO 🦋

go read these next, they're all in the same friend group:

• Kernel file ./include/linux/mm_types.h
• softleaf_t(9)
• struct folio(9)
• struct ptdesc(9)
• vm_fault_t(9)
• enum fault_flag(9)

okay that's the whole page, you ate that 💅 this one lives in ./include/linux and the date on it is October 2026, so yeah, your girl is timestamped and documented, periodt ✨🎀🦋