Re: [virtio-comment] [PATCH v1 1/8] admin: Add theory of operation for device migration

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 07, 2023 at 03:57:29PM +0800, Zhu, Lingshan wrote:
> 
> 
> On 11/7/2023 3:22 PM, Michael S. Tsirkin wrote:
> > On Tue, Nov 07, 2023 at 12:05:12PM +0800, Jason Wang wrote:
> > > > > > > One thing that you ignore is that, hypervisor can use what you
> > > > > > > invented as a transport for VF, no?
> > > > > > > 
> > > > > > No. by design,
> > > > > It works like hypervisor traps the virito config and forwards it to admin
> > > > > virtqueue and starts the device via device context.
> > > > It needs more granular support than the management framework of device context.
> > > It doesn't otherwise it is a design defect as you can't recover the
> > > device context in the destination.
> > > 
> > > Let me give you an example:
> > > 
> > > 1) in the case of live migration, dst receive migration byte flows and
> > > convert them into device context
> > > 2) in the case of transporting, hypervisor traps virtio config and
> > > convert them into the device context
> > > 
> > > I don't see anything different in this case. Or can you give me an example?
> > "trap virtio config" means "trap writes into virtio config" presumably?
> > config can change itself without driver doing anything. Hypervisor
> > can't trap it then. This is one of the problems with Lingshan's
> > SUSPEND bit - what happens with these config changes in underspecified.
> It should send a config interrupt and increase its generation.

/me shrugs

> By the way, is it buggy if a device suspend itself?
> Is needs_reset better even not properly handled by virito driver

NEEDS_RESET turned out not to be a great design.

-- 
MST


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