apic_soft_disable(9)

💅 apic_soft_disable — a kernel API manual moment (section 9 of the kernel API manual, bestie)

okay so you found your way to apic_soft_disable(9) and honestly? iconic. this is the Kernel API Manual and we're about to get into it. 🎀

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✨ NAME ✨

apic_soft_disable — clears and software-disables the local APIC on hotplug. literally that's the whole job. no cap. 🦋

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🌸 SYNOPSIS 🌸

void apic_soft_disable (void );

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🎀 ARGUMENTS 🎀

• void — no arguments. that's it. zero. none. the void is voiding. 💀

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🔥 DESCRIPTION 🔥

okay so here's the tea ☕ — unlike disable_local_APIC, this function does not touch the enable bit in MSR_IA32_APICBASE. not even a little. hands off. 🙈

why, you ask? because clearing that bit on systems based on the 3 wire APIC bus would require a hardware reset, since the APIC would lose track of bus arbitration. like, the whole vibe would be ruined and you can't just undo it. 😭

now, on systems with FSB delivery, APICBASE could be disabled — but only if it's guaranteed that no interrupt is sent to the APIC while it's in that state. and here's the messy part: it's not clear from the SDM whether it still responds to INIT/SIPI messages. 🫠 so we stay on the safe side and use software disable. periodt. 💅

ngl bestie, the whole energy here is "we could, but should we?" and the answer is no. safe side only. 🧚

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⭐ SEE ALSO ⭐

• the kernel file ./arch/x86/kernel/apic/apic.c
• lapic_get_maxlvt(9)
• clear_local_APIC(9)
• disable_local_APIC(9)
• sync_Arb_IDs(9)
• setup_local_APIC(9)
• init_apic_mappings(9)
• spurious_interrupt(9)
• connect_bsp_APIC(9)
• disconnect_bsp_APIC(9)
• apic_bsp_setup(9)

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and that's the whole page, bestie! 🫶 this one lives in ./arch/x86/kernel/apic and it's dated October 2026 — so like, future vibes. go read the other APIC pages, they ate. 👑🌈💖