kvm: x86: Fix kvm_arch_fixup_msi_route for remap-less case

The AMD IOMMU does not (yet) support interrupt remapping. But
kvm_arch_fixup_msi_route assumes that all implementations do and crashes
when the AMD IOMMU is used in KVM mode.

Fixes: 8b5ed7df ("intel_iommu: add support for split irqchip")
Reported-by: Christopher Goldsworthy <christopher.goldsworthy@outlook.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Message-Id: <48ae78d8-58ec-8813-8680-6f407ea46041@siemens.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/kvm.c

@@ -3669,6 +3669,10 @@ int kvm_arch_fixup_msi_route(struct kvm_irq_routing_entry *route,
         MSIMessage src, dst;
         X86IOMMUClass *class = X86_IOMMU_GET_CLASS(iommu);
 
+        if (!class->int_remap) {
+            return 0;
+        }
+
         src.address = route->u.msi.address_hi;
         src.address <<= VTD_MSI_ADDR_HI_SHIFT;
         src.address |= route->u.msi.address_lo;