RE: [PATCH v5 17/27] vfio/cxl: Own the whole component register BAR

[Manish Honap]

> -----Original Message-----
> From: Alex Williamson <alex@xxxxxxxxxxx>
> Sent: Tuesday, September 22, 2026 7:44 AM
> To: Manish Honap <mhonap@xxxxxxxxxx>
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> Subject: Re: [PATCH v5 17/27] vfio/cxl: Own the whole component register
> BAR
> 
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> 
> On Thu, 17 Sep 2026 00:05:30 +0530
> <mhonap@xxxxxxxxxx> wrote:
> 
> > From: Manish Honap <mhonap@xxxxxxxxxx>
> >
> > devm_cxl_probe_mem() maps the component registers through the CXL
> > core, which by default claims each HDM and RAS sub-block. That
> > collides with the full-BAR request vfio-pci-core makes when the guest opens
> the device.
> >
> > After the component registers are discovered, declare the containing
> > BAR owned with cxl_reg_map_add_owned_resource(). The core then
> > ioremaps the sub-blocks without requesting them, so vfio-pci-core owns
> > the whole BAR and the requests do not collide.
> >
> > Assisted-by: LLM
> > Signed-off-by: Manish Honap <mhonap@xxxxxxxxxx>
> > ---
> >  drivers/vfio/pci/cxl/vfio_cxl_core.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/vfio/pci/cxl/vfio_cxl_core.c
> > b/drivers/vfio/pci/cxl/vfio_cxl_core.c
> > index 0d92e6a409c1..5c8a63833a43 100644
> > --- a/drivers/vfio/pci/cxl/vfio_cxl_core.c
> > +++ b/drivers/vfio/pci/cxl/vfio_cxl_core.c
> > @@ -89,6 +89,15 @@ static int vfio_cxl_init_device(struct
> vfio_pci_core_device *vdev)
> >               goto err;
> >       }
> >
> > +     /*
> > +      * vfio-pci-core requests the whole component-register BAR when the
> > +      * guest opens the device. Declare that BAR owned so the CXL core
> > +      * ioremaps the HDM and RAS sub-blocks without claiming them, and the
> > +      * full-BAR request does not collide.
> > +      */
> > +     cxl_reg_map_add_owned_resource(&cxl->cxlds.reg_map,
> > +                                    pci_resource_n(pdev,
> > + pdev->hdm->hdm_bar));
> > +
> 
> The result of this operation is setting a singleton "owned" pointer to this
> resource, whereas the name suggests it's adding the resource to some set of
> owned resources.  Is "set" really the more idiomatic verb for this than "add"?
> Thanks,
> 

Yes. I will rename it to cxl_reg_map_set_owned_resource() in v6.

> Alex
> 
> >       if (!cxl->cxlds.reg_map.component_map.hdm_decoder.valid) {
> >               pci_err(pdev, "vfio-cxl: HDM decoder registers not found\n");
> >               ret = -ENODEV;