hw/i386/x86: Fix PIC interrupt handling if APIC is globally disabled

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>

hw/i386/x86.c

@@ -520,7 +520,7 @@ static void x86_nmi(NMIState *n, int cpu_index, Error **errp)
     CPU_FOREACH(cs) {
         X86CPU *cpu = X86_CPU(cs);
 
-        if (cpu->apic_state) {
+        if (cpu_is_apic_enabled(cpu->apic_state)) {
             apic_deliver_nmi(cpu->apic_state);
         } else {
             cpu_interrupt(cs, CPU_INTERRUPT_NMI);
@@ -555,7 +555,7 @@ static void pic_irq_request(void *opaque, int irq, int level)
     X86CPU *cpu = X86_CPU(cs);
 
     trace_x86_pic_interrupt(irq, level);
-    if (cpu->apic_state && !kvm_irqchip_in_kernel() &&
+    if (cpu_is_apic_enabled(cpu->apic_state) && !kvm_irqchip_in_kernel() &&
         !whpx_apic_in_platform()) {
         CPU_FOREACH(cs) {
             cpu = X86_CPU(cs);

hw/intc/apic_common.c

@@ -62,6 +62,19 @@ uint64_t cpu_get_apic_base(DeviceState *dev)
     }
 }
 
+bool cpu_is_apic_enabled(DeviceState *dev)
+{
+    APICCommonState *s;
+
+    if (!dev) {
+        return false;
+    }
+
+    s = APIC_COMMON(dev);
+
+    return s->apicbase & MSR_IA32_APICBASE_ENABLE;
+}
+
 void cpu_set_apic_tpr(DeviceState *dev, uint8_t val)
 {
     APICCommonState *s;

include/hw/i386/apic.h

@@ -10,6 +10,7 @@ void apic_deliver_nmi(DeviceState *d);
 int apic_get_interrupt(DeviceState *s);
 int cpu_set_apic_base(DeviceState *s, uint64_t val);
 uint64_t cpu_get_apic_base(DeviceState *s);
+bool cpu_is_apic_enabled(DeviceState *s);
 void cpu_set_apic_tpr(DeviceState *s, uint8_t val);
 uint8_t cpu_get_apic_tpr(DeviceState *s);
 void apic_init_reset(DeviceState *s);