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

[Christoph Hellwig <hch@lst.de>]

On Tue, Dec 06, 2022 at 09:05:05AM -0400, Jason Gunthorpe wrote:
> In this case Intel has a real PCI SRIOV VF to expose to the guest,
> with a full VF RID.

RID?

> The proper VFIO abstraction is the variant PCI
> driver as this series does. We want to use the variant PCI drivers
> because they properly encapsulate all the PCI behaviors (MSI, config
> space, regions, reset, etc) without requiring re-implementation of this
> in mdev drivers.

I don't think the code in this series has any chance of actually
working.  There is a lot of state associated with a NVMe subsystem,
controller and namespace, such as the serial number, subsystem NQN,
namespace uniqueue identifiers, Get/Set features state, pending AENs,
log page content.  Just migrating from one device to another without
capturing all this has no chance of actually working.

> I don't think we know enough about this space at the moment to fix a
> specification to one path or the other, so I hope the TPAR will settle
> on something that can support both models in SW and people can try
> things out.

I've not seen anyone from Intel actually contributing to the live
migration TPAR, which is almost two month old by now.