spapr: Add a "no HPT" encoding to HTAB migration stream

Add a "no HPT" encoding (using value -1) to the HTAB migration
stream (in the place of HPT size) when the guest doesn't allocate HPT.
This will help the target side to match target HPT with the source HPT
and thus enable successful migration.
Suggested-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NBharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr.c

@@ -1560,13 +1560,19 @@ static int htab_save_setup(QEMUFile *f, void *opaque)
     sPAPRMachineState *spapr = opaque;
 
     /* "Iteration" header */
-    qemu_put_be32(f, spapr->htab_shift);
+    if (!spapr->htab_shift) {
+        qemu_put_be32(f, -1);
+    } else {
+        qemu_put_be32(f, spapr->htab_shift);
+    }
 
     if (spapr->htab) {
         spapr->htab_save_index = 0;
         spapr->htab_first_pass = true;
     } else {
-        assert(kvm_enabled());
+        if (spapr->htab_shift) {
+            assert(kvm_enabled());
+        }
     }
 
 
@@ -1712,7 +1718,12 @@ static int htab_save_iterate(QEMUFile *f, void *opaque)
     int rc = 0;
 
     /* Iteration header */
-    qemu_put_be32(f, 0);
+    if (!spapr->htab_shift) {
+        qemu_put_be32(f, -1);
+        return 0;
+    } else {
+        qemu_put_be32(f, 0);
+    }
 
     if (!spapr->htab) {
         assert(kvm_enabled());
@@ -1746,7 +1757,12 @@ static int htab_save_complete(QEMUFile *f, void *opaque)
     int fd;
 
     /* Iteration header */
-    qemu_put_be32(f, 0);
+    if (!spapr->htab_shift) {
+        qemu_put_be32(f, -1);
+        return 0;
+    } else {
+        qemu_put_be32(f, 0);
+    }
 
     if (!spapr->htab) {
         int rc;
@@ -1790,6 +1806,11 @@ static int htab_load(QEMUFile *f, void *opaque, int version_id)
 
     section_hdr = qemu_get_be32(f);
 
+    if (section_hdr == -1) {
+        spapr_free_hpt(spapr);
+        return 0;
+    }
+
     if (section_hdr) {
         Error *local_err = NULL;