Re: [PATCH v6 06/31] vfio/pci: Add the CXL provider ops registration interface

[Alex Williamson <alex@shazbot.org>]

On Fri, 16 Oct 2026 21:48:13 +0530
<mhonap@nvidia.com> wrote:

> From: Manish Honap <mhonap@nvidia.com>
> 
> vfio-pci-core must stay free of any CXL header dependency, so CXL Type-2
> handling lives in a separate vfio-cxl module that plugs in a set of
> callbacks.
> 
> Add the registration interface:
> - vfio-cxl registers a single struct vfio_cxl_ops at module_init
> - vfio-pci-core stores it under an rwsem.
> 
> A second registration is refused with -EBUSY.
> 
> The owner field will be used to pin vfio-cxl for the lifetime of each
> bound CXL device.
> 
> Assisted-by: LLM
> Signed-off-by: Manish Honap <mhonap@nvidia.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 24 ++++++++++++++++++++++++
>  include/linux/vfio_pci_core.h    | 10 ++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 6757054e9d87..2cc5dd20396c 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -2178,6 +2178,30 @@ static void vfio_pci_vga_uninit(struct vfio_pci_core_device *vdev)
>  					      VGA_RSRC_LEGACY_MEM);
>  }
>  
> +static const struct vfio_cxl_ops *vfio_pci_cxl_ops;
> +static DECLARE_RWSEM(vfio_pci_cxl_ops_rwsem);
> +
> +int vfio_pci_core_register_cxl_ops(const struct vfio_cxl_ops *ops)
> +{
> +	guard(rwsem_write)(&vfio_pci_cxl_ops_rwsem);
> +
> +	if (vfio_pci_cxl_ops)
> +		return -EBUSY;
> +
> +	vfio_pci_cxl_ops = ops;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(vfio_pci_core_register_cxl_ops);
> +
> +void vfio_pci_core_unregister_cxl_ops(const struct vfio_cxl_ops *ops)
> +{
> +	guard(rwsem_write)(&vfio_pci_cxl_ops_rwsem);
> +
> +	if (vfio_pci_cxl_ops == ops)
> +		vfio_pci_cxl_ops = NULL;
> +}
> +EXPORT_SYMBOL_GPL(vfio_pci_core_unregister_cxl_ops);
> +
>  int vfio_pci_core_init_dev(struct vfio_device *core_vdev)
>  {
>  	struct vfio_pci_core_device *vdev =
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index 9a1674c152aa..9fe0d1a3a370 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -66,6 +66,16 @@ struct vfio_pci_device_ops {
>  			       size_t nr_ranges);
>  };
>  
> +struct vfio_cxl_ops {
> +	int	(*init)(struct vfio_pci_core_device *vdev);
> +	void	(*release)(struct vfio_pci_core_device *vdev);
> +	/* Pinned per bound CXL device so vfio-cxl cannot unload under usage */
> +	struct module *owner;
> +};

A forward declaration would be sufficient and cleaner here.  It doesn't
buy us anything to start defining the structure until we begin to use
it.  Thanks,

Alex

> +
> +int vfio_pci_core_register_cxl_ops(const struct vfio_cxl_ops *ops);
> +void vfio_pci_core_unregister_cxl_ops(const struct vfio_cxl_ops *ops);
> +
>  #if IS_ENABLED(CONFIG_VFIO_PCI_DMABUF)
>  int vfio_pci_core_fill_phys_vec(struct phys_vec *phys_vec,
>  				struct vfio_region_dma_range *dma_ranges,