Re: [PATCH v2 03/10] PCI/LUO: Forward prepare()/freeze()/cancel() callbacks to driver

[David Matlack <dmatlack@google.com>]

On 2025-09-30 01:38 PM, Jason Gunthorpe wrote:
> On Mon, Sep 29, 2025 at 07:11:06PM -0700, Chris Li wrote:
> > On Mon, Sep 29, 2025 at 10:48 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > >
> > > On Tue, Sep 16, 2025 at 12:45:11AM -0700, Chris Li wrote:
> > > > After the list of preserved devices is constructed, the PCI subsystem can
> > > > now forward the liveupdate request to the driver.
> > >
> > > This also seems completely backwards for how iommufd should be
> > > working. It doesn't want callbacks triggered on prepare, it wants to
> > > drive everything from its own ioctl.
> > 
> > This series is about basic PCI device support, not IOMMUFD.
> > 
> > > Let's just do one thing at a time please and make this series about
> > > iommufd to match the other luo series for iommufd.
> > 
> > I am confused by you.
> > 
> > > non-iommufd cases can be proposed in their own series.
> > 
> > This is that non-iommufd series.
> 
> Then don't do generic devices until we get iommufd done and you have a
> meaningful in-tree driver to consume what you are adding.

I agree with Jason. I don't think we can reasonably make the argument
that we need this series until we have actualy use-cases for it.

I think we should focus on vfio-pci device preservation next, and use
that to incrementally drive whatever changes are necessary to the PCI
and generic device layer bit by bit.

For example, once we a basic vfio-pci device preservation working, we
can start thinking about how to handle when that device is a VF, and we
have to start also preserving the SR-IOV state on the PF and get the PF
driver involved in the process. At that point we can discuss how to
solve that specific problem. Maybe the solution will look something like
this series, maybe it will look like something else. There is open
design space.

Without approaching it this way, I don't see how we can't reasonably
argue that anything in this series is necessary. And I suspect some
parts of this series truly are unnecessary, at least in the short term.
In our internal implementation, the only dependent device that truly
needed to participate is the PF driver when a VF is preserved.
Everything else (e.g. pcieport callbacks) have just been no-ops.