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>

1 files changed, 13 insertions, 0 deletions

diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
index 16ab40a..d8fc1e2 100644
--- a/hw/intc/apic_common.c
+++ b/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;