Re: [RFC PATCH v2 2/3] vfio: Set the priority of the VFIO VM state change handler explicitly

[Shenming Lu <lushenming@huawei.com>]

On 2021/1/27 5:36, Alex Williamson wrote:
> On Wed, 9 Dec 2020 16:09:18 +0800
> Shenming Lu <lushenming@huawei.com> wrote:
> 
>> In the VFIO VM state change handler, VFIO devices are transitioned
>> in the _SAVING state, which should keep them from sending interrupts.
> 
> Is this comment accurate?  It's my expectation that _SAVING has no
> bearing on a device generating interrupts.  Interrupt generation must
> be allowed to continue so long as the device is _RUNNING.  Thanks,
> 

To be more accurate, the _RUNNING bit in device_state is cleared in the
VFIO VM state change handler when stopping the VM. And if the device continues
to send interrupts after this, how can we save the states of device interrupts
in the stop-and-copy phase?...

Thanks,
Shenming

> Alex
> 
>> Then we can save the pending states of all interrupts in the GIC VM
>> state change handler (on ARM).
>>
>> So we have to set the priority of the VFIO VM state change handler
>> explicitly (like virtio devices) to ensure it is called before the
>> GIC's in saving.
>>
>> Signed-off-by: Shenming Lu <lushenming@huawei.com>
>> Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>
>> ---
>>  hw/vfio/migration.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index 3b9de1353a..97ea82b100 100644
>> --- a/hw/vfio/migration.c
>> +++ b/hw/vfio/migration.c
>> @@ -862,7 +862,8 @@ static int vfio_migration_init(VFIODevice *vbasedev,
>>      register_savevm_live(id, VMSTATE_INSTANCE_ID_ANY, 1, &savevm_vfio_handlers,
>>                           vbasedev);
>>  
>> -    migration->vm_state = qemu_add_vm_change_state_handler(vfio_vmstate_change,
>> +    migration->vm_state = qdev_add_vm_change_state_handler(vbasedev->dev,
>> +                                                           vfio_vmstate_change,
>>                                                             vbasedev);
>>      migration->migration_state.notify = vfio_migration_state_notifier;
>>      add_migration_state_change_notifier(&migration->migration_state);
> 
> .
>