reserve_top_address(9)

✨ reserve_top_address(9) ✨

okay so bestie, welcome to the Kernel API Manual — this one's a tiny function with a big job, and it's genuinely iconic for it 💅

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🌸 NAME 🌸

reserve_top_address — it reserves a hole in the top of the kernel address space, no cap 🕳️👑

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🦋 SYNOPSIS 🦋

void reserve_top_address(unsigned long reserve);

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🎀 ARGUMENTS 🎀

• reserve — the size of the hole you wanna reserve. yeah that's it, that's the whole argument 🫶

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💖 DESCRIPTION 💖

So like… you can use this to relocate the fixmap area and poke a hole in the top of the kernel address space, which makes room for a hypervisor 🧚✨

literally just "excuse me, moving the fixmap over, gotta carve out some space up top" and the kernel is like "say less" 💀

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🌈 SEE ALSO 🌈

• Kernel file ./arch/x86/mm/pgtable.c
• p4d_set_huge(9)
• p4d_clear_huge(9)
• pud_set_huge(9)
• pmd_set_huge(9)
• pud_clear_huge(9)
• pmd_clear_huge(9)
• pmd_free_pte_page(9)

like a whole little pgtable friend group, go say hi 👑🍓

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mwah 💜 that's the whole page — brought to you by ./arch/x86/mm, stamped October 2026, and calling itself reserve_top_address(9) one more time for the people in the back 📣 slay.