RE: [PATCH v5 08/27] vfio/pci: Fall back to plain vfio-pci when CXL init fails

[Manish Honap]

> -----Original Message-----
> From: Alex Williamson <alex@xxxxxxxxxxx>
> Sent: Tuesday, September 22, 2026 7:45 AM
> To: Manish Honap <mhonap@xxxxxxxxxx>
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> Subject: Re: [PATCH v5 08/27] vfio/pci: Fall back to plain vfio-pci when CXL init
> fails
> 
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> 
> On Thu, 17 Sep 2026 00:05:21 +0530
> <mhonap@xxxxxxxxxx> wrote:
> 
> > From: Manish Honap <mhonap@xxxxxxxxxx>
> >
> > A CXL Type-2 device is also a valid plain vfio-pci device. If the
> > vfio-cxl provider cannot bring it up as Type-2, failing the bind would
> > regress a device that previously worked as plain vfio-pci.
> >
> > Make a non-deferred CXL init failure non-fatal: log it, drop the
> > provider reference, leave cxl_ops NULL, and continue driving the
> > device as plain vfio-pci. The -EPROBE_DEFER path added earlier still
> > retries rather than falling back.
> >
> > Assisted-by: LLM
> > Signed-off-by: Manish Honap <mhonap@xxxxxxxxxx>
> > ---
> >  drivers/vfio/pci/vfio_pci_core.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c
> > b/drivers/vfio/pci/vfio_pci_core.c
> > index a63a4f5228b8..9a75c30b67e2 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -2271,9 +2271,17 @@ static int vfio_pci_core_cxl_init(struct
> vfio_pci_core_device *vdev)
> >               vfio_pci_put_cxl_ops(ops);
> >               return ret;
> >       }
> > +     /*
> > +      * Any other failure is non-fatal: a CXL device that cannot be brought
> > +      * up as Type-2 still works as plain vfio-pci, so log and continue
> > +      * rather than failing the bind.
> > +      */
> >       if (ret) {
> > +             pci_warn(vdev->pdev,
> > +                      "CXL init failed (%d), continuing as plain vfio-pci\n",
> > +                      ret);
> >               vfio_pci_put_cxl_ops(ops);
> > -             return ret;
> > +             return 0;
> >       }
> >
> >       vdev->cxl_ops = ops;
> 
> Why isn't this the initial implementation in patch 6?  I don't fully understand
> why patches 7 and 8 are circling back to modify the broken behavior
> established in patch 6 rather than resolving it in the patch where it was
> introduced.
> 
> Perhaps rephrasing the message, "... continuing without CXL support".  "plain
> vfio-pci" doesn't mean anything to a user that only knows to use vfio-pci.
> Thanks,
> 

Agreed. Sorry for this churn; In v6 I will fold 07 and 08 into 06, so the provider
hookup lands with its final error handling: -EPROBE_DEFER from the
provider defers the bind, and any other init error leaves the device
bound without the CXL extensions.

I will also update the error message to mention "continuing without CXL support"
and remove any references to "plain vfio-pci".

> Alex