intel_iommu: fix migration breakage on mr switch

Migration is broken after the vfio integration work:

qemu-kvm: AHCI: Failed to start FIS receive engine: bad FIS receive buffer address
qemu-kvm: Failed to load ich9_ahci:ahci
qemu-kvm: error while loading state for instance 0x0 of device '0000:00:1f.2/ich9_ahci'
qemu-kvm: load of migration failed: Operation not permitted

The problem is that vfio work introduced dynamic memory region
switching (actually it is also used for future PT mode), and this memory
region layout is not properly delivered to destination when migration
happens. Solution is to rebuild the layout in post_load.

Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1459906
Fixes: 558e0024 ("intel_iommu: allow dynamic switch of IOMMU region")
Reviewed-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/i386/intel_iommu.c

@@ -2337,11 +2337,26 @@ static void vtd_iommu_notify_flag_changed(MemoryRegion *iommu,
     }
 }
 
+static int vtd_post_load(void *opaque, int version_id)
+{
+    IntelIOMMUState *iommu = opaque;
+
+    /*
+     * Memory regions are dynamically turned on/off depending on
+     * context entry configurations from the guest. After migration,
+     * we need to make sure the memory regions are still correct.
+     */
+    vtd_switch_address_space_all(iommu);
+
+    return 0;
+}
+
 static const VMStateDescription vtd_vmstate = {
     .name = "iommu-intel",
     .version_id = 1,
     .minimum_version_id = 1,
     .priority = MIG_PRI_IOMMU,
+    .post_load = vtd_post_load,
     .fields = (VMStateField[]) {
         VMSTATE_UINT64(root, IntelIOMMUState),
         VMSTATE_UINT64(intr_root, IntelIOMMUState),