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

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Message-ID: <CALzav=fci3jPft+SXJ6tPG3=jRX7jjJPwnP=zWAb2Sui++vKPw@mail.gmail.com>
Date: Fri, 3 Oct 2025 09:03:36 -0700
From: David Matlack <dmatlack@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
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>, Brian Vazquez <brianvv@...gle.com>
Subject: Re: [PATCH v2 03/10] PCI/LUO: Forward prepare()/freeze()/cancel()
 callbacks to driver

On Fri, Oct 3, 2025 at 5:04 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Thu, Oct 02, 2025 at 04:42:17PM -0700, David Matlack wrote:
> > 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:
> > > > 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.
> >
> > So far we have had to support vfio-pci, pci-pf-stub, and idpf as PF
> > drivers, and nvme looks like it's coming soon :(
>
> How much effort did you put into moving them to vfio though? Hack Hack
> in the kernel is easy, but upstreaming may be very hard :\
>
> Shutting down enough of the PF kernel driver to safely kexec is almost
> the same as unbinding it completely.

I think it's totally fair to tell us to replace pci-pf-stub with
vfio-pci. That gets rid of one PF driver.

idpf cannot be easily replaced with vfio-pci, since the PF is also
used for host networking. Brian Vazquez from Google will be giving a
talk about the idpf support at LPC so we can revisit this topic there.
We took the approach of only preserving the SR-IOV configuration in
the PF, everything else gets reset (so no DMA mapping preservation, no
driver state preservation, etc.).

We haven't looked into nvme yet so we'll have to revisit that discussion later.