Re: [virtio-dev] Re: [virtio-comment] Re: [VIRTIO PCI PATCH v5 1/1] transport-pci: Add freeze_mode to virtio_pci_common_cfg

Zhu, Lingshan
2023-09-20T07:30:28Z

On 9/20/2023 3:24 PM, Chen, Jiqian wrote:
> Hi Lingshan,
> It seems you reply to the wrong email thread. They are not related to my patch.
These reply to Parva's comments.
@Parva, if you want to discuss more about live migration, please reply
in my thread, lets don't flood here.
>
> On 2023/9/20 15:06, Zhu, Lingshan wrote:
>>
>> On 9/20/2023 2:58 PM, Parav Pandit wrote:
>>>> From: Chen, Jiqian <Jiqian.Chen@amd.com>
>>>> Sent: Wednesday, September 20, 2023 12:03 PM
>>>> If driver write 0 to reset device, can the SUSPEND bit be cleared?
>>> It must as reset operation, resets everything else and so the suspend too.
>>>
>>>> (pci_pm_resume->virtio_pci_restore->virtio_device_restore-
>>>>> virtio_reset_device)
>>>> If SUSPEND is cleared, then during the reset process in Qemu, I can't judge if
>>>> the reset request is from guest restore process or not, and then I can't change
>>>> the reset behavior.
>>> Reset should not be influenced by suspend.
>>> Suspend should do the work of suspend and reset to do the reset.
>>>
>>> The problem to overcome in [1] is, resume operation needs to be synchronous as it involves large part of context to resume back, and hence just asynchronously setting DRIVER_OK is not enough.
>>> The sw must verify back that device has resumed the operation and ready to answer requests.
>> this is not live migration, all device status and other information still stay in the device, no need to "resume" context, just resume running.
>>
>> Like resume from a failed LM.
>>> This is slightly different flow than setting the DRIVER_OK for the first time device initialization sequence as it does not involve large restoration.
>>>
>>> So, to merge two ideas, instead of doing DRIVER_OK to resume, the driver should clear the SUSPEND bit and verify that it is out of SUSPEND.
>>>
>>> Because driver is still in _OK_ driving the device flipping the SUSPEND bit.
>> Please read the spec, it says:
>> The driver MUST NOT clear a device status bit
>>
>>

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