Re: [PATCH v4 08/27] vfio/cxl: Add the vfio-cxl module skeleton

[Alex Williamson <alex@shazbot.org>]

On Thu, 13 Aug 2026 15:06:12 +0530
<mhonap@nvidia.com> wrote:

> From: Manish Honap <mhonap@nvidia.com>
> 
> Add the vfio-cxl module that vfio-pci loads on demand for CXL Type-2
> devices. It registers a set of callbacks with vfio-pci-core at
> module_init and drops them at exit; the callbacks are stubs here and
> are filled in by later patches.
> 
> VFIO_CXL depends on CXL_BUS and builds as vfio-cxl.ko, which
> request_module("vfio-cxl") resolves through MODULE_ALIAS.
> 
> Signed-off-by: Manish Honap <mhonap@nvidia.com>
> ---
>  MAINTAINERS                          |  7 +++++
>  drivers/vfio/pci/Kconfig             |  2 ++
>  drivers/vfio/pci/Makefile            |  2 ++
>  drivers/vfio/pci/cxl/Kconfig         | 11 ++++++++
>  drivers/vfio/pci/cxl/Makefile        |  3 ++
>  drivers/vfio/pci/cxl/vfio_cxl_core.c | 41 ++++++++++++++++++++++++++++
>  6 files changed, 66 insertions(+)
>  create mode 100644 drivers/vfio/pci/cxl/Kconfig
>  create mode 100644 drivers/vfio/pci/cxl/Makefile
>  create mode 100644 drivers/vfio/pci/cxl/vfio_cxl_core.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c665bf8f1a28..aa8cecbc4cf2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -28312,6 +28312,13 @@ L:	kvm@vger.kernel.org
>  S:	Maintained
>  F:	drivers/vfio/cdx/*
>  
> +VFIO CXL DRIVER
> +M:	Manish Honap <mhonap@nvidia.com>
> +L:	kvm@vger.kernel.org
> +L:	linux-cxl@vger.kernel.org
> +S:	Supported
> +F:	drivers/vfio/pci/cxl/
> +
>  VFIO DRIVER
>  M:	Alex Williamson <alex@shazbot.org>
>  L:	kvm@vger.kernel.org
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index 296bf01e185e..c3f54fc8ccc0 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -70,6 +70,8 @@ source "drivers/vfio/pci/virtio/Kconfig"
>  
>  source "drivers/vfio/pci/nvgrace-gpu/Kconfig"
>  
> +source "drivers/vfio/pci/cxl/Kconfig"
> +
>  source "drivers/vfio/pci/qat/Kconfig"
>  
>  source "drivers/vfio/pci/xe/Kconfig"

It seems fair to put this above the variant driver Kconfigs rather than
bury it among them.

> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index 6138f1bf241d..c3031070a1f3 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -21,6 +21,8 @@ obj-$(CONFIG_VIRTIO_VFIO_PCI) += virtio/
>  
>  obj-$(CONFIG_NVGRACE_GPU_VFIO_PCI) += nvgrace-gpu/
>  
> +obj-$(CONFIG_VFIO_CXL) += cxl/
> +
>  obj-$(CONFIG_QAT_VFIO_PCI) += qat/
>  
>  obj-$(CONFIG_XE_VFIO_PCI) += xe/

Here again, cxl is a feature of vfio-pci-core.  I'd promote it to
between vfio-pci-core and vfio-pci.  The earlier linking also has the
benefit that in the typical case it will be available before the
builtin drivers (but keep the deferred loading behavior).  Thanks,

Alex

> diff --git a/drivers/vfio/pci/cxl/Kconfig b/drivers/vfio/pci/cxl/Kconfig
> new file mode 100644
> index 000000000000..1392fa4ed15d
> --- /dev/null
> +++ b/drivers/vfio/pci/cxl/Kconfig
> @@ -0,0 +1,11 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +config VFIO_CXL
> +	tristate "VFIO support for CXL Type-2 devices"
> +	depends on CXL_BUS && CXL_MEM
> +	select VFIO_PCI_CORE
> +	help
> +	  Add CXL HDM handling to vfio-pci so a CXL Type-2 device, such as a
> +	  CXL-attached accelerator, can be assigned to a virtual machine.
> +	  vfio-pci loads this module on demand when it binds a CXL device.
> +
> +	  If you don't know what to do here, say N.
> diff --git a/drivers/vfio/pci/cxl/Makefile b/drivers/vfio/pci/cxl/Makefile
> new file mode 100644
> index 000000000000..8501bf626108
> --- /dev/null
> +++ b/drivers/vfio/pci/cxl/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-$(CONFIG_VFIO_CXL) += vfio-cxl.o
> +vfio-cxl-y := vfio_cxl_core.o
> diff --git a/drivers/vfio/pci/cxl/vfio_cxl_core.c b/drivers/vfio/pci/cxl/vfio_cxl_core.c
> new file mode 100644
> index 000000000000..cbec7319452c
> --- /dev/null
> +++ b/drivers/vfio/pci/cxl/vfio_cxl_core.c
> @@ -0,0 +1,41 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * VFIO support for CXL Type-2 devices.
> + *
> + * Copyright (c) 2026 NVIDIA Corporation & Affiliates
> + */
> +
> +#include <linux/module.h>
> +#include <linux/vfio_pci_core.h>
> +
> +static int vfio_cxl_init_device(struct vfio_pci_core_device *vdev)
> +{
> +	return 0;
> +}
> +
> +static void vfio_cxl_release_device(struct vfio_pci_core_device *vdev)
> +{
> +}
> +
> +static const struct vfio_cxl_ops vfio_cxl_ops = {
> +	.init_device	= vfio_cxl_init_device,
> +	.release_device	= vfio_cxl_release_device,
> +	.owner		= THIS_MODULE,
> +};
> +
> +static int __init vfio_cxl_init(void)
> +{
> +	return vfio_pci_core_register_cxl_ops(&vfio_cxl_ops);
> +}
> +
> +static void __exit vfio_cxl_exit(void)
> +{
> +	vfio_pci_core_unregister_cxl_ops(&vfio_cxl_ops);
> +}
> +
> +module_init(vfio_cxl_init);
> +module_exit(vfio_cxl_exit);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("VFIO support for CXL Type-2 devices");
> +MODULE_ALIAS("vfio-cxl");