Re: [Qemu-devel] [RFC 23/29] migration: new cmd MIG_CMD_POSTCOPY_RESUME

[Peter Xu]

On Fri, Aug 04, 2017 at 03:04:19PM +0800, Peter Xu wrote:
> On Thu, Aug 03, 2017 at 12:05:41PM +0100, Dr. David Alan Gilbert wrote:
> 
> [...]
> 
> > > +static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
> > > +{
> > > +    /*
> > > +     * This means source VM is ready to resume the postcopy migration.
> > > +     * It's time to switch state and release the fault thread to
> > > +     * continue service page faults.
> > > +     */
> > > +    migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_RECOVER,
> > > +                      MIGRATION_STATUS_POSTCOPY_ACTIVE);
> > > +    qemu_sem_post(&mis->postcopy_pause_sem_fault);
> > 
> > Is it worth sanity checking that you were in RECOVER at this point?
> 
> Yeah, it never hurts.  Will do.

Not sure whether this would be good (note: I returned 0 in the if):

diff --git a/migration/savevm.c b/migration/savevm.c
index b7843c2..b34f59b 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1709,6 +1709,12 @@ static int 
loadvm_postcopy_handle_run(MigrationIncomingState *mis)
 
 static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
 {
+    if (mis->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
+        error_report("%s: illegal resume received", __func__);
+        /* Don't fail the load, only for this. */
+        return 0;
+    }
+
     /*
      * This means source VM is ready to resume the postcopy migration.
      * It's time to switch state and release the fault thread to

Basically I just don't want to crash the dest VM (it holds hot dirty
pages) even if it receives a faulty RESUME command.

-- 
Peter Xu