intel-iommu: update root_scalable before switching as during post_load

We need check whether passthrough is enabled during
vtd_switch_address_space() by checking the context entries. This
requires the root_scalable to be set correctly otherwise we may try to
check legacy rsvd bits instead of scalable ones.

Fixing this by updating root_scalable before switching the address
spaces during post_load.

Fixes: fb43cf73 ("intel_iommu: scalable mode emulation")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220317080522.14621-1-jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>

hw/i386/intel_iommu.c

@@ -3073,13 +3073,6 @@ 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);
-
     /*
      * We don't need to migrate the root_scalable because we can
      * simply do the calculation after the loading is complete.  We
@@ -3089,6 +3082,13 @@ static int vtd_post_load(void *opaque, int version_id)
      */
     vtd_update_scalable_state(iommu);
 
+    /*
+     * 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;
 }