QEMU<->ACPI BIOS CPU hotplug interface -------------------------------------- QEMU supports CPU hotplug via ACPI. This document describes the interface between QEMU and the ACPI BIOS. ACPI GPE block (IO ports 0xafe0-0xafe3, byte access): ----------------------------------------- Generic ACPI GPE block. Bit 2 (GPE.2) used to notify CPU hot-add/remove event to ACPI BIOS, via SCI interrupt. CPU present bitmap (IO port 0xaf00-0xaf1f, 1-byte access): --------------------------------------------------------------- One bit per CPU. Bit position reflects corresponding CPU APIC ID. Read-only. CPU hot-add/remove notification: ----------------------------------------------------- QEMU sets/clears corresponding CPU bit on hot-add/remove event. CPU present map read by ACPI BIOS GPE.2 handler to notify OS of CPU hot-(un)plug events.