it would prevent starting guest with incorrect configs
where interrupts couldn't be delivered to CPUs with
APIC IDs > 254.

Signed-off-by: Igor Mammedov <imamm...@redhat.com>
---
 hw/i386/pc.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 40eb43b..f7070e0 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -68,6 +68,7 @@
 #include "qapi-visit.h"
 #include "qom/cpu.h"
 #include "hw/nmi.h"
+#include "hw/i386/intel_iommu.h"
 
 /* debug PC/ISA interrupts */
 //#define DEBUG_IRQ
@@ -1264,6 +1265,18 @@ void pc_machine_done(Notifier *notifier, void *data)
                             sizeof(pcms->boot_cpus_le));
         }
     }
+
+    if (pcms->apic_id_limit > 255) {
+        IntelIOMMUState *iommu = INTEL_IOMMU_DEVICE(x86_iommu_get_default());
+
+        if (!iommu || !iommu->x86_iommu.intr_supported ||
+            iommu->intr_eim != ON_OFF_AUTO_ON) {
+            error_report("current -smp configuration requires "
+                         "Extended Interrupt Mode enabled. "
+                         "IOMMU should have eim=on option set");
+            exit(EXIT_FAILURE);
+        }
+    }
 }
 
 void pc_guest_info_init(PCMachineState *pcms)
-- 
2.7.4


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