Re: [PATCH v4 14/27] vfio: Add CXL region type for the HDM region

[Alex Williamson]

On Thu, 13 Aug 2026 15:06:18 +0530
<mhonap@xxxxxxxxxx> wrote:

> From: Manish Honap <mhonap@xxxxxxxxxx>
> 
> A CXL Type-2 device exposes its HDM memory to the guest as a dedicated
> VFIO region rather than a PCI BAR. Add a CXL region type and a memory
> sub-type for it; vfio-cxl registers the window under these so userspace
> can discover and map it.
> 
> Signed-off-by: Manish Honap <mhonap@xxxxxxxxxx>
> ---
>  include/uapi/linux/vfio.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 5de618a3a5ee..540e62312671 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -345,6 +345,7 @@ struct vfio_region_info_cap_type {
>  #define VFIO_REGION_TYPE_GFX                    (1)
>  #define VFIO_REGION_TYPE_CCW			(2)
>  #define VFIO_REGION_TYPE_MIGRATION_DEPRECATED   (3)
> +#define VFIO_REGION_TYPE_CXL			(4)
>  
>  /* sub-types for VFIO_REGION_TYPE_PCI_* */
>  
> @@ -373,6 +374,10 @@ struct vfio_region_info_cap_type {
>  /* sub-types for VFIO_REGION_TYPE_GFX */
>  #define VFIO_REGION_SUBTYPE_GFX_EDID            (1)
>  
> +/* sub-types for VFIO_REGION_TYPE_CXL */
> +/* CXL.mem HDM region of a Type-2 device, mmap-able */
> +#define VFIO_REGION_SUBTYPE_CXL_MEM		(1)
> +
>  /**
>   * struct vfio_region_gfx_edid - EDID region layout.
>   *

CXL has a PCI vendor ID, it's even used in the dvsec capability.  Why
not use a PCI vendor type region?  Thanks,

Alex