xen-hvm: Clean up xen_ram_alloc() error handling

xen_ram_alloc() dies with hw_error() on error, even though its caller
ram_block_add() handles errors just fine.  Add an Error **errp
parameter and use it.

Leave case RUN_STATE_INMIGRATE alone, because that looks like some
kind of warning.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
diff --git a/exec.c b/exec.c
index 7f0ce42..c268c36 100644
--- a/exec.c
+++ b/exec.c
@@ -1474,6 +1474,7 @@
     RAMBlock *block;
     RAMBlock *last_block = NULL;
     ram_addr_t old_ram_size, new_ram_size;
+    Error *err = NULL;
 
     old_ram_size = last_ram_offset() >> TARGET_PAGE_BITS;
 
@@ -1483,7 +1484,12 @@
     if (!new_block->host) {
         if (xen_enabled()) {
             xen_ram_alloc(new_block->offset, new_block->max_length,
-                          new_block->mr);
+                          new_block->mr, &err);
+            if (err) {
+                error_propagate(errp, err);
+                qemu_mutex_unlock_ramlist();
+                return -1;
+            }
         } else {
             new_block->host = phys_mem_alloc(new_block->max_length,
                                              &new_block->mr->align);