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

[Manish Honap]

> -----Original Message-----
> From: Alex Williamson <alex@xxxxxxxxxxx>
> Sent: Friday, August 28, 2026 4:14 AM
> To: Manish Honap <mhonap@xxxxxxxxxx>
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> Subject: Re: [PATCH v4 14/27] vfio: Add CXL region type for the HDM region
> 
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> 
> 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

Yes, I will switch to a PCI vendor-type region with the CXL vendor ID instead of CXL
region type.

Manish