Re: [PATCH 5/5] hisi_acc_vfio_pci: bugfix live migration function without VF device driver

[liulongfang <liulongfang@huawei.com>]

On 2024/12/9 21:51, Jason Gunthorpe wrote:
> On Fri, Dec 06, 2024 at 05:33:12PM +0800, Longfang Liu wrote:
>> If the driver of the VF device is not loaded in the Guest OS,
>> then perform device data migration. The migrated data address will
>> be NULL.
>> The live migration recovery operation on the destination side will
>> access a null address value, which will cause access errors.
>>
>> Therefore, live migration of VMs without added VF device drivers
>> does not require device data migration.
>> In addition, when the queue address data obtained by the destination
>> is empty, device queue recovery processing will not be performed.
> 
> This seems very strange, why can't you migrate over the null DMA addr?
> Shouldn't this be fixed on the receiving side?
>

There are two parts to the process here:
First: If the source does not add the device driver in the Guest VM.
Then except the dma address is empty, other device parameters are also
empty data. Therefore, there is no need to migrate this data of the device.

Second: If the source adds the driver in the VM, but the received DMA
address is empty due to data reading or migration process. This kind of
empty address needs to be processed at the destination and cannot be
written to the device.

Thanks,
Longfang.

> Jason
> .
>