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

On Wed, Oct 11, 2023 at 02:43:37AM -0400, Michael S. Tsirkin
wrote:
> > Btw, what is that intel thing everyone is talking about?  And why
> > would the virtio core support vendor specific behavior like that?
> 
> It's not a thing it's Zhu Lingshan :) intel is just one of the
vendors
> that implemented vdpa support and so Zhu Lingshan from intel is working
> on vdpa and has also proposed virtio spec extensions for migration.
> intel's driver is called ifcvf.  vdpa composes all this stuff that is
> added to vfio in userspace, so it's a different approach.
Well, so let's call it virtio live migration instead of intel.

And please work all together in the virtio committee that you have
one way of communication between controlling and controlled functions.
If one extension does it one way and the other a different way that's
just creating a giant mess.

Hi Christoph,
> From: Christoph Hellwig <hch at infradead.org>
> Sent: Wednesday, October 11, 2023 12:29 PM
> 
> On Wed, Oct 11, 2023 at 02:43:37AM -0400, Michael S. Tsirkin wrote:
> > > Btw, what is that intel thing everyone is talking about?  And why
> > > would the virtio core support vendor specific behavior like that?
> >
> > It's not a thing it's Zhu Lingshan :) intel is just one of the
vendors
> > that implemented vdpa support and so Zhu Lingshan from intel is
> > working on vdpa and has also proposed virtio spec extensions for
migration.
> > intel's driver is called ifcvf.  vdpa composes all this stuff that
is
> > added to vfio in userspace, so it's a different approach.
> 
> Well, so let's call it virtio live migration instead of intel.
> 
> And please work all together in the virtio committee that you have one way
of
> communication between controlling and controlled functions.
> If one extension does it one way and the other a different way that's
just
> creating a giant mess.
We in virtio committee are working on VF device migration where:
VF = controlled function
PF = controlling function

The second proposal is what Michael mentioned from Intel that somehow combine
controlled and controlling function as single entity on VF.

The main reasons I find it weird are:
1. it must always need to do mediation to do fake the device reset, and flr
flows
2. dma cannot work as you explained for complex device state
3. it needs constant knowledge of each tiny things for each virtio device type

Such single entity appears a bit very weird to me but maybe it is just me.

On Tue, Oct 10, 2023 at 11:59:26PM -0700, Christoph Hellwig
wrote:
> On Wed, Oct 11, 2023 at 02:43:37AM -0400, Michael S. Tsirkin wrote:
> > > Btw, what is that intel thing everyone is talking about?  And why
> > > would the virtio core support vendor specific behavior like that?
> > 
> > It's not a thing it's Zhu Lingshan :) intel is just one of the
vendors
> > that implemented vdpa support and so Zhu Lingshan from intel is
working
> > on vdpa and has also proposed virtio spec extensions for migration.
> > intel's driver is called ifcvf.  vdpa composes all this stuff that
is
> > added to vfio in userspace, so it's a different approach.
> 
> Well, so let's call it virtio live migration instead of intel.
> 
> And please work all together in the virtio committee that you have
> one way of communication between controlling and controlled functions.
> If one extension does it one way and the other a different way that's
> just creating a giant mess.
Absolutely, this is exactly what I keep suggesting. Thanks for
bringing this up, will help me drive the point home!

-- 
MST

On 10/11/2023 2:59 PM, Christoph Hellwig wrote:
> On Wed, Oct 11, 2023 at 02:43:37AM -0400, Michael S. Tsirkin wrote:
>>> Btw, what is that intel thing everyone is talking about?  And why
>>> would the virtio core support vendor specific behavior like that?
>> It's not a thing it's Zhu Lingshan :) intel is just one of the
vendors
>> that implemented vdpa support and so Zhu Lingshan from intel is working
>> on vdpa and has also proposed virtio spec extensions for migration.
>> intel's driver is called ifcvf.  vdpa composes all this stuff that
is
>> added to vfio in userspace, so it's a different approach.
> Well, so let's call it virtio live migration instead of intel.
>
> And please work all together in the virtio committee that you have
> one way of communication between controlling and controlled functions.
> If one extension does it one way and the other a different way that's
> just creating a giant mess.
I hope so, Jason Wang has proposed a solution to cooperate, but sadly
rejected...
>
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