VFIO_IOMMU_S...ISTER_MEMORY(9)

🎀 VFIO_IOMMU_S...ISTER_MEMORY(9) 🎀

okay bestie, this one's coming at you straight out of the Kernel API Manual, and it's one of those ioctl pages that looks scary but is actually so chill once you read it. it's giving "small page, very specific job" energy and honestly? we love a specialist 💅

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✨ NAME ✨

• VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY — this is the ioctl, and its number is literally spelled out for you: _IOW(VFIO_TYPE, VFIO_BASE + 18, struct vfio_iommu_spapr_register_memory). yes, the struct in the ioctl signature is the register one even though the ioctl is the unregister one — that's not a typo, that's just how it is, don't come for me 🫶

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🦋 SYNOPSIS 🦋

VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY

that's it. that's the whole synopsis. iconic minimalism, no notes 🌸

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💖 DESCRIPTION 💖

so what does it actually do? it unregisters user space memory. specifically, memory that you (or somebody) already registered with VFIO_IOMMU_SPAPR_REGISTER_MEMORY. think of it as the "undo" button for that registration — you put the memory in, now you're taking it back out 🎀

for its parameters, it uses vfio_iommu_spapr_register_memory. same struct, both directions, iykyk.

ngl the whole thing is very "one in, one out" — if you never registered the memory in the first place, this is not the page that's gonna save you 😭

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🔥 SEE ALSO 🔥

the kernel file itself lives at ./include/uapi/linux/vfio.h — go read it, it's right there, it's free ⭐

and here's the whole friend group, all of them (9) sections so you know they're kernel-API famous 👑:

• VFIO_GET_API_VERSION(9)
• VFIO_CHECK_EXTENSION(9)
• VFIO_SET_IOMMU(9)
• VFIO_GROUP_SET_CONTAINER(9)
• VFIO_GROUP_UNSET_CONTAINER(9)
• VFIO_GROUP_GET_DEVICE_FD(9)
• struct vfio_region_gfx_edid(9)
• VFIO_DEVICE_RESET(9)
• VFIO_DEVICE_GET_GFX_DMABUF(9)

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and that's the page, bestie 💜 this little gem came from ./include/uapi/linux, dated October 2026, and it goes out to VFIO_IOMMU_S...ISTER_MEMORY(9) — slay, go unregister some memory, periodt 🌈