migration: Test for disabled features on reception

Right now, if we receive a compressed page while this features are
disabled, Bad Things (TM) can happen.  Just add a test for them.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>

--

I had XBZRLE here also, but it don't need extra resources on
destination, only on source.  Additionally libvirt don't enable it on
destination, so don't put it here.

- initialize invalid_flags at declaration time.
- remove extra space (peter)

migration/ram.c

@@ -2455,7 +2455,7 @@ static int ram_load_postcopy(QEMUFile *f)
 
 static int ram_load(QEMUFile *f, void *opaque, int version_id)
 {
-    int flags = 0, ret = 0;
+    int flags = 0, ret = 0, invalid_flags = 0;
     static uint64_t seq_iter;
     int len = 0;
     /*
@@ -2472,6 +2472,9 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
         ret = -EINVAL;
     }
 
+    if (!migrate_use_compression()) {
+        invalid_flags |= RAM_SAVE_FLAG_COMPRESS_PAGE;
+    }
     /* This RCU critical section can be very long running.
      * When RCU reclaims in the code start to become numerous,
      * it will be necessary to reduce the granularity of this
@@ -2492,6 +2495,15 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
         flags = addr & ~TARGET_PAGE_MASK;
         addr &= TARGET_PAGE_MASK;
 
+        if (flags & invalid_flags) {
+            if (flags & invalid_flags & RAM_SAVE_FLAG_COMPRESS_PAGE) {
+                error_report("Received an unexpected compressed page");
+            }
+
+            ret = -EINVAL;
+            break;
+        }
+
         if (flags & (RAM_SAVE_FLAG_ZERO | RAM_SAVE_FLAG_PAGE |
                      RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
             RAMBlock *block = ram_block_from_stream(f, flags);