copy_from_user_nmi(9)

✨ copy_from_user_nmi(9) ✨

okay so bestie, welcome to the Kernel API Manual 💖 — today's main character is copy_from_user_nmi, and she's lowkey iconic.

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🌸 NAME 🌸

copy_from_user_nmi — NMI safe copy from user 💅

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🎀 SYNOPSIS 🎀

unsigned long copy_from_user_nmi (void *to , const void __user *from ,
unsigned long n );

like, yes, that's the whole signature, no cap ✨

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🦋 ARGUMENTS 🦋

• to — pointer to the destination buffer, aka where the bytes are gonna land 🫶
• from — pointer to a user space address of the current task 👀
• n — the number of bytes to copy, fr fr, that's literally it 💜

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🌈 RETURN 🌈

she returns the number of not copied bytes 😭 — so 0 means success, i.e. all bytes copied. slay 💅

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👑 DESCRIPTION 👑

okay so here's the vibe check: contrary to other copy_from_user variants, this function can be called from NMI context 🔥. And despite the name, she's not restricted to NMI context either — it's safe to be called from any other context as well, no gatekeeping here 🧚.

She disables pagefaults across the copy, which means a fault will abort the copy 💀 — yes, like, mid-copy, done, no more bytes, periodt.

For NMI context invocations, this relies on the nested NMI work to allow atomic faults from the NMI path; the nested NMI paths are careful to preserve CR2 ⭐. iykyk.

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💫 SEE ALSO 💫

Kernel file ./arch/x86/lib/usercopy.c 📁

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that's the whole page bestie, go read the source and stan 🍓

with love from ./arch/x86/lib, dated October 2026, manual page copy_from_user_nmi(9) — mwah 💋