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

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Message-ID: <CACePvbXdzx5rfS1qKkFYtL-yizQiht_evge-jWo0F2ruobgkZA@mail.gmail.com>
Date: Thu, 2 Oct 2025 22:24:59 -0700
From: Chris Li <chrisl@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: David Matlack <dmatlack@...gle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Len Brown <lenb@...nel.org>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org, 
	Pasha Tatashin <tatashin@...gle.com>, Jason Miu <jasonmiu@...gle.com>, 
	Vipin Sharma <vipinsh@...gle.com>, Saeed Mahameed <saeedm@...dia.com>, 
	Adithya Jayachandran <ajayachandra@...dia.com>, Parav Pandit <parav@...dia.com>, William Tu <witu@...dia.com>, 
	Mike Rapoport <rppt@...nel.org>, Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v2 03/10] PCI/LUO: Forward prepare()/freeze()/cancel()
 callbacks to driver

On Thu, Oct 2, 2025 at 4:21 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Thu, Oct 02, 2025 at 02:31:08PM -0700, David Matlack wrote:
> > I'm saying the only drivers that actually needed to implement Live
> > Update driver callbacks have been vfio-pci and PF drivers. The
> > vfio-pci support doesn't exist yet upstream, and we are planning to
> > use FD preservation there. So we don't know if driver callbacks will
> > be needed for that.
>
> I don't expect driver callbacks trough the pci subsystem, and I think
> they should be removed from this series.

Per suggestion from David as well. I will remove the driver callback
from the PCI series.

>
> As I said the flow is backwards from what we want. The vfio driver
> gets a luo FD from an ioctl, and it goes through and calls into luo
> and pci with that session object to do all the required serialization.
>
> Any required callbacks should be routed through luo based on creating
> preserved objects within luo and providing ops to luo.
>
> There is no other way to properly link things to sessions.

As David pointed out in the other email, the PCI also supports other
non vfio PCI devices which do not have the FD and FD related sessions.
That is the original intent for the LUO PCI subsystem.

> > And we don't care about PF drivers until we get to
> > supporting SR-IOV. So the driver callbacks all seem unnecessary at
> > this point.
>
> I guess we will see, but I'm hoping we can get quite far using
> vfio-pci as the SRIOV PF driver and don't need to try to get a big PF
> in-kernel driver entangled in this.

Yes, vfio-pci is a big series as well. Getting a NIC might be easier
to get the PF DMA working with a live update but that will be thrown
away once we have the vfio-pci as the real user. Actually getting the
pci-pf-stub driver working would be a smaller and reasonable step to
justify the PF support in LUO PCI.

Chris