Re: [PATCH V1 11/32] cpu: disable ticks when suspended

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Steven Sistare (steven.sistare@oracle.com) wrote:
> On 9/11/2020 1:53 PM, Dr. David Alan Gilbert wrote:
> > * Steve Sistare (steven.sistare@oracle.com) wrote:
> >> After cprload, the guest console misbehaves.  You must type 8 characters
> >> before any are echoed to the terminal.  Qemu was not sending interrupts
> >> to the guest because the QEMU_CLOCK_VIRTUAL timers_state.cpu_clock_offset
> >> was bad.  The offset is usually updated at cprsave time by the path
> >>
> >>   save_cpr_snapshot()
> >>     vm_stop()
> >>       do_vm_stop()
> >>         if (runstate_is_running())
> >>           cpu_disable_ticks();
> >>             timers_state.cpu_clock_offset = cpu_get_clock_locked();
> >>
> >> However, if the guest is in RUN_STATE_SUSPENDED, then cpu_disable_ticks is
> >> not called.  Further, the earlier transition to suspended in
> >> qemu_system_suspend did not disable ticks.  To fix, call cpu_disable_ticks
> >> from save_cpr_snapshot.
> >>
> >> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> > 
> > Are you saying this is really a more generic bug with migrating when
> > suspended and we should fix this anyway?
> 
> Yes.  Or when suspended and calling save_vmstate(), or qmp_xen_save_devices_state().
> Each of those functions needs the same fix unless someone identifies a more
> centralized way in the state transition logic to disable ticks.

OK, in that case please split this out of the series and we can take a
fix as normal;  please cc in mtosatti@redhat.com .

Dave

> 
> - Steve
> 
> >> ---
> >>  migration/savevm.c | 5 +++++
> >>  1 file changed, 5 insertions(+)
> >>
> >> diff --git a/migration/savevm.c b/migration/savevm.c
> >> index f101039..00f493b 100644
> >> --- a/migration/savevm.c
> >> +++ b/migration/savevm.c
> >> @@ -2729,6 +2729,11 @@ void save_cpr_snapshot(const char *file, const char *mode, Error **errp)
> >>          return;
> >>      }
> >>  
> >> +    /* Update timers_state before saving.  Suspend did not so do. */
> >> +    if (runstate_check(RUN_STATE_SUSPENDED)) {
> >> +        cpu_disable_ticks();
> >> +    }
> >> +
> >>      vm_stop(RUN_STATE_SAVE_VM);
> >>  
> >>      ret = qemu_savevm_state(f, op, errp);
> >> -- 
> >> 1.8.3.1
> >>
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK