[PATCH 1/2] hw/i386/x86: Fix PIC interrupt handling if APIC globally disabled

[Bernhard Beschow]

QEMU populates the apic_state attribute of x86 CPUs if supported by real
hardware. Even when the APIC is globally disabled by a guest, this attribute
stays populated. This means that the APIC code paths are still used in this
case. 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. The CPUID feature flag for the APIC
  [...] is also set to 0.

Fix this by checking the APIC feature flag rather than apic_state when deciding
whether PIC or APIC behavior is required. This fixes some real-world BIOSes.

Notice that presence of the CPUID_APIC flag implies that apic_state is non-NULL.

[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>
---
 hw/i386/x86.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index 2b6291ad8d..a753d1aeca 100644
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -516,10 +516,10 @@ static void x86_nmi(NMIState *n, int cpu_index, Error 
**errp)
     CPU_FOREACH(cs) {
         X86CPU *cpu = X86_CPU(cs);
 
-        if (!cpu->apic_state) {
-            cpu_interrupt(cs, CPU_INTERRUPT_NMI);
-        } else {
+        if (cpu->env.features[FEAT_1_EDX] & CPUID_APIC) {
             apic_deliver_nmi(cpu->apic_state);
+        } else {
+            cpu_interrupt(cs, CPU_INTERRUPT_NMI);
         }
     }
 }
@@ -551,8 +551,8 @@ 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() &&
-        !whpx_apic_in_platform()) {
+    if ((cpu->env.features[FEAT_1_EDX] & CPUID_APIC) &&
+        !kvm_irqchip_in_kernel() && !whpx_apic_in_platform()) {
         CPU_FOREACH(cs) {
             cpu = X86_CPU(cs);
             if (apic_accept_pic_intr(cpu->apic_state)) {
-- 
2.43.0