RE: [virtio-comment] Re: [PATCH v1 3/8] device-context: Define the device context fields for device migration

[Parav Pandit <parav@nvidia.com>]

> From: Jason Wang <jasowang@redhat.com>
> Sent: Wednesday, November 1, 2023 6:03 AM
> 
> On Tue, Oct 31, 2023 at 1:17âPM Parav Pandit <parav@nvidia.com> wrote:
> >
> >
> >
> > > From: virtio-comment@lists.oasis-open.org
> > > <virtio-comment@lists.oasis- open.org> On Behalf Of Jason Wang
> > > Sent: Tuesday, October 31, 2023 7:07 AM
> > >
> > > On Mon, Oct 30, 2023 at 12:28âPM Parav Pandit <parav@nvidia.com> wrote:
> > > >
> > > >
> > > > > From: Jason Wang <jasowang@redhat.com>
> > > > > Sent: Monday, October 30, 2023 9:35 AM
> > > > >
> > > > > å 2023/10/26 11:50, Parav Pandit åé:
> > > > > >> From: virtio-comment@lists.oasis-open.org
> > > > > >> <virtio-comment@lists.oasis- open.org> On Behalf Of Jason
> > > > > >> Wang For example, you still haven't succeeded in defining
> passthrough.
> > > > > > It was defined on 19th Oct in [1].
> > > > > > What part is not clear to you in definition of passthrough device?
> > > > > >
> > > > > > [1]
> > > > > > https://lore.kernel.org/virtio-
> > > > > comment/PH0PR12MB5481EA6A4D0C64C5AF6D3A
> > > > > > 57DCD4A@PH0PR12MB5481.namprd12.prod.outlook.com/
> > > > >
> > > > >
> > > > > Let me copy-paste it again:
> > > > >
> > > > > For example, assuming you are correct, you still fail to explain
> > > > >
> > > > > 1) what is trapped and what's not, or what's the boundary
> > > > Passthrough definition was replied few times.
> > > > One of them is here,
> > > > https://lore.kernel.org/virtio-
> > > comment/PH0PR12MB5481EA6A4D0C64C5AF6D3A
> > > > 57DCD4A@PH0PR12MB5481.namprd12.prod.outlook.com/
> > > > I donât know what you mean by 'explain'. What do you want to be
> explained?
> > > > What is trapped is listed in
> > > > https://lore.kernel.org/virtio-
> > > comment/PH0PR12MB5481EA6A4D0C64C5AF6D3A
> > > > 57DCD4A@PH0PR12MB5481.namprd12.prod.outlook.com/
> > > > What is not trapped is also listed in
> > > > https://lore.kernel.org/virtio-
> > > comment/PH0PR12MB5481EA6A4D0C64C5AF6D3A
> > > > 57DCD4A@PH0PR12MB5481.namprd12.prod.outlook.com/
> > > > So what more do you want to explain in there?
> > >
> > > You explained that MSI-X is trapped but not the others. People may know
> why.
> > > or what's the boundary to choose to trap or not.
> > >
> > If a platform can support without trapping, it can be avoided as well and can
> be added in the future.
> 
> Who is going to do that synchronization?
Lets first bring that hypervisor sw design before discussing phantom problem solving.
All necessary modules will be involved in synchronization depending on how its done in future.

> 
> >
> > > >
> > > > > 2) if the hypervisor is not developed with those assumptions,
> > > > > things can work
> > > > What to explain in #2. :)
> > > > Things can expand when such hypervisor is born.
> > >
> > > So the point is still, to make your proposal to be useful in more use cases.
> > >
> > When a use case arise, device context can be expanded.
> 
> It's not device context.
>
I donât see why not. It is stored in the device.
Remapping part will be hypervisor specific, so it may be stored in platform specific migration data.
 
> > No point in making things no one implements or not present in hypervisor.
> > The infrastructure is extendible so spec is covered for it.
> 
> It would be problematic if you stick to claim "passthrough" but not.

I donât know what this means. I am not debating passthrough/non-passthrough.
What is inside the device, will be part of device-context.
What is part of the platform content, will be part of platform context.
Since this is generic to all types of PCI devices, I donât see a need to over-solve it now in virtio.