Linux Virtualization - Oct 2023 - [PATCH vfio 10/11] vfio/virtio: Expose admin commands over virtio device

On 10/12/2023 9:27 PM, Jason Gunthorpe wrote:
> On Thu, Oct 12, 2023 at 06:29:47PM +0800, Zhu, Lingshan wrote:
>
>> sorry for the late reply, we have discussed this for weeks in virtio
mailing
>> list. I have proposed a live migration solution which is a config space
solution.
> I'm sorry that can't be a serious proposal - config space can't
do
> DMA, it is not suitable.
config space only controls the live migration process and config the 
related facilities.
We don't use config space to transfer data.

The new added registers work like queue_enable or features.

For example, we use DMA to report dirty pages and MMIO to fetch the 
dirty data.

I remember in another thread you said:"you can't use DMA for any 
migration flows"

And I agree to that statement, so we use config space registers to 
control the flow.

Thanks,
Zhu Lingshan
>
> Jason
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On Fri, Oct 13, 2023 at 06:28:34PM +0800, Zhu, Lingshan
wrote:
> 
> 
> On 10/12/2023 9:27 PM, Jason Gunthorpe wrote:
> 
>     On Thu, Oct 12, 2023 at 06:29:47PM +0800, Zhu, Lingshan wrote:
> 
> 
>         sorry for the late reply, we have discussed this for weeks in
virtio mailing
>         list. I have proposed a live migration solution which is a config
space solution.
> 
>     I'm sorry that can't be a serious proposal - config space
can't do
>     DMA, it is not suitable.
> 
> config space only controls the live migration process and config the
related
> facilities.
> We don't use config space to transfer data.
> 
> The new added registers work like queue_enable or features.
> 
> For example, we use DMA to report dirty pages and MMIO to fetch the dirty
data.
> 
> I remember in another thread you said:"you can't use DMA for any
migration
> flows"
> 
> And I agree to that statement, so we use config space registers to control
the
> flow.
> 
> Thanks,
> Zhu Lingshan
> 
> 
>     Jason
> 
If you are using dma then I don't see what's wrong with admin vq.
dma is all it does.