On 11/20/2023 2:59 PM, Peter Xu wrote:
> On Mon, Nov 13, 2023 at 10:33:50AM -0800, Steve Sistare wrote:
>> A vm in the suspended state is not completely stopped. The VCPUs have been
>> paused, but the cpu clock still runs, and runstate notifiers for the
>> transition to stopped have not been called. Modify vm_stop_force_state to
>> completely stop the vm if the current state is suspended, to be called for
>> live migration and snapshots.
>>
>> Suggested-by: Peter Xu <pet...@redhat.com>
>> Signed-off-by: Steve Sistare <steven.sist...@oracle.com>
>> ---
>> system/cpus.c | 8 ++++++--
>> 1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/system/cpus.c b/system/cpus.c
>> index f72c4be..c772708 100644
>> --- a/system/cpus.c
>> +++ b/system/cpus.c
>> @@ -255,6 +255,8 @@ void cpu_interrupt(CPUState *cpu, int mask)
>> static int do_vm_stop(RunState state, bool send_stop, bool force)
>> {
>> int ret = 0;
>> + bool running = runstate_is_running();
>> + bool suspended = runstate_check(RUN_STATE_SUSPENDED);
>>
>> if (qemu_in_vcpu_thread()) {
>> qemu_system_vmstop_request_prepare();
>> @@ -267,10 +269,12 @@ static int do_vm_stop(RunState state, bool send_stop,
>> bool force)
>> return 0;
>> }
>>
>> - if (runstate_is_running()) {
>> + if (running || (suspended && force)) {
>> runstate_set(state);
>> cpu_disable_ticks();
>
> Not directly relevant, but this is weird that I just notice.
>
> If we disable ticks before stopping vCPUs, IIUC it means vcpus can see
> stall ticks. I checked the vm_start() and indeed that one did it in the
> other way round: we'll stop vCPUs before stopping the ticks.
>
>> - pause_all_vcpus();
>> + if (running) {
>> + pause_all_vcpus();
>> + }
>> vm_state_notify(0, state);
>> if (send_stop) {
>> qapi_event_send_stop();
>
> IIUC the "force" is not actually needed. It's only used when SUSPENDED,
> right?
>
> In general, considering all above, I'm wondering something like this would
> be much cleaner (and dropping force)?
If we drop force, then all calls to vm_stop will completely stop the suspended
state, eg an hmp "stop" command. This causes two problems. First, that is a
change
in user-visible behavior for something that currently works, vs the migration
code
where we are fixing brokenness. Second, it does not quite work, because the
state
becomes RUN_STATE_PAUSED, so the suspended state is forgotten, and the hmp
"cont"
will try to set the running state. I could fix that by introducing a new state
RUN_STATE_SUSPENDED_STOPPED, but again it is a user-visible change in existing
behavior. (I even implemented that while developing, then I realized it was
not
needed to fix the migration bugs.)
- Steve
> ===8<===
> static int do_vm_stop(RunState state, bool send_stop)
> {
> + bool suspended = runstate_check(RUN_STATE_SUSPENDED);
> + bool running = runstate_is_running();
> int ret = 0;
>
> - if (runstate_is_running()) {
> + /*
> + * RUNNING: VM and vCPUs are all running
> + * SUSPENDED: VM is running, VCPUs are stopped
> + * Others: VM and vCPUs are all stopped
> + */
> +
> + /* Whether do we need to stop vCPUs? */
> + if (running) {
> + pause_all_vcpus();
> + }
> +
> + /* Whether do we need to stop the VM in general? */
> + if (running || suspended) {
> runstate_set(state);
> cpu_disable_ticks();
> - pause_all_vcpus();
> vm_state_notify(0, state);
> if (send_stop) {
> qapi_event_send_stop();
>
