Re: [RFC PATCH 5/5] nvme-vfio: Add a document for the NVMe device

[Jason Gunthorpe]

On Tue, Dec 06, 2022 at 03:00:02PM +0100, Christoph Hellwig wrote:
> > >From what I understood this series basically allows two Intel devices
> > to pass a big opaque blob of data. Intel didn't document what is in
> > that blob, so I assume it captures everything you mention above.
> 
> Which would be just as bad, because it then changes the IDs under
> the live OS on a restore.  This is not something that can be done
> behind the back of the hypervisors / control plane OS.

Sorry, what live OS?

In the VFIO restore model there is no "live OS" on resume. The
load/resume cycle is as destructive as reset to the vfio device.

When qemu operates vfio the destination CPU will not be running until
the load/resume of all the VFIO devices is completed.

So from the VM perspective it sees a complete no change, so long as
the data blob causes the destination vfio device to fully match the
source, including all IDs, etc.

Jason