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QEMU populates the apic_state attribute of x86 CPUs if supported by real hardware or if SMP is active. When handling interrupts, it just checks whether apic_state is populated to route the interrupt to the PIC or to the APIC. However, chapter 10.4.3 of [1] requires that: When IA32_APIC_BASE[11] is 0, the processor is functionally equivalent to an IA-32 processor without an on-chip APIC. This means that when apic_state is populated, QEMU needs to check for the MSR_IA32_APICBASE_ENABLE flag in addition. Implement this which fixes some real-world BIOSes. [1] Intel 64 and IA-32 Architectures Software Developer's Manual, Vol. 3A: System Programming Guide, Part 1 Signed-off-by: Bernhard Beschow <shentey@gmail.com> Message-Id: <20240106132546.21248-3-shentey@gmail.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>