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

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Message-ID: <20251002232153.GK3195829@ziepe.ca>
Date: Thu, 2 Oct 2025 20:21:53 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: David Matlack <dmatlack@...gle.com>
Cc: Chris Li <chrisl@...nel.org>, 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 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.

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.

> 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.

Jason