diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
index 198892ebdf..6ea14c4c56 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -498,9 +498,19 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid, bool restore,
     if ( restore )
     {
         /*
-         * Account for feature which have been disabled by default since Xen 4.13,
-         * so migrated-in VM's don't risk seeing features disappearing.
+         * Xen 4.14 introduced support to move the guest's CPUID data in the
+         * migration stream.  Previously, the destination side would invent a
+         * policy out of thin air in the hopes that it was ok.
+         *
+         * This restore path is used for incoming VMs with no CPUID data
+         * i.e. originated on Xen 4.13 or earlier.  We must invent a policy
+         * compatible with what Xen 4.13 would have done on the same hardware.
+         *
+         * Specifically:
+         * - Clamp max leaves.
+         * - Re-enable features which have become (possibly) off by default.
          */
+
         p->basic.rdrand = test_bit(X86_FEATURE_RDRAND, host_featureset);
         p->feat.hle = test_bit(X86_FEATURE_HLE, host_featureset);
         p->feat.rtm = test_bit(X86_FEATURE_RTM, host_featureset);
@@ -510,7 +520,6 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid, bool restore,
             p->feat.mpx = test_bit(X86_FEATURE_MPX, host_featureset);
         }
 
-        /* Clamp maximum leaves to the ones supported on 4.12. */
         p->basic.max_leaf = min(p->basic.max_leaf, 0xdu);
         p->feat.max_subleaf = 0;
         p->extd.max_leaf = min(p->extd.max_leaf, 0x8000001c);