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

[Alex Williamson <alex@shazbot.org>]

On Thu, 17 Sep 2026 00:05:21 +0530
<mhonap@nvidia.com> wrote:

> From: Manish Honap <mhonap@nvidia.com>
> 
> 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@nvidia.com>
> ---
>  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,

Alex