hmm_range_fault(9)

💅 hmm_range_fault(9) 💅

okay so bestie, welcome to the Kernel API Manual — this one's a section 9 situation, which means it's kernel-internals territory. and honestly? she's kind of a big deal. let's get into it 🫶

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✨ NAME ✨

hmm_range_fault — the girl whose whole job is to try to fault some address in a virtual address range. that's it, that's the mission. 🎯

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🌸 SYNOPSIS 🌸

int hmm_range_fault (struct hmm_range *range );

literally one function, one argument. minimalism. she ate. 💅

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🎀 ARGUMENTS 🎀

• range — the argument structure. yeah that's the whole description bestie, the manpage said it and i'm not gonna invent lore 😭 it's just your hmm_range struct.

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💖 DESCRIPTION 💖

so what does she return? 0 on success ✨ — or one of these error codes, and you will be reading them:

• -EINVAL — invalid arguments, or the mm or virtual address is sitting in an invalid vma (e.g., a device file vma). nope, not that one, try again 🙈
• -ENOMEM — out of memory. the classic. the icon. the reason we can't have nice things 😭
• -EPERM — invalid permission (e.g., you're asking for write and the range is read only). bold of you to ask, honestly 💀
• -EBUSY — the range has been invalidated, so the caller needs to wait for the invalidation to finish. hold on hold on hold on 🫠
• -EFAULT — a page was requested to be valid and could not be made valid, ie it has no backing VMA or it is illegal to access. the audacity 🚨

ngl, she's similar to get_user_pages, except — and this is the slay part — she can read the page tables without mutating them (ie causing faults). no cap, she's just looking respectfully 👀✨

now the part where you need to pay attention, bestie:

the mmap lock must be held by the caller and will remain held on return. do not fumble this. 🔒

new users should prefer hmm_range_fault_unlocked_timeout unless they specifically need to keep the mmap lock held across the call. like, genuinely specifically. 🫶

and one more thing — this helper cannot support VMAs whose fault handlers need to drop the mmap lock. that's not a vibe thing, that's a hard limitation, so don't come for her when it doesn't work 💀

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🦋 SEE ALSO 🦋

go read these too, i'm obsessed with a cross-referenced manpage:

• Kernel file ./mm/hmm.c
• hmm_range_fault_unlocked_timeout(9)
• hmm_dma_map_alloc(9)
• hmm_dma_map_free(9)
• hmm_dma_map_pfn(9)
• hmm_dma_unmap_pfn(9)

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and that's the whole page, bestie — no notes, she's perfect 💅✨

signing off from ./mm, dated October 2026 — catch you in the next manpage, muah 🎀💖🦋