> -----Original Message-----
> From: Alex Williamson <[email protected]>
> Sent: Thursday, August 27, 2026 2:42 AM
> To: Manish Honap <[email protected]>
> Cc: [email protected]; Ankit Agrawal <[email protected]>; [email protected];
> [email protected]; [email protected]; Srirangan Madhavan
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; Yishai Hadas
> <[email protected]>; Shameer Kolothum Thodi
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; Neo Jia
> <[email protected]>; Krishnakant Jaju <[email protected]>; Vikram Sethi
> <[email protected]>; Zhi Wang <[email protected]>; linux-
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; linux-
> [email protected]; [email protected]; [email protected]
> Subject: Re: [PATCH v4 06/27] vfio/pci: Add CXL ops registration interface
>
> External email: Use caution opening links or attachments
>
>
> On Thu, 13 Aug 2026 15:06:10 +0530
> <[email protected]> wrote:
>
> > From: Manish Honap <[email protected]>
> >
> > 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, and vfio-pci-core stores it
> > under a mutex.
> >
> > The owner field lets a later patch pin vfio-cxl for the lifetime of
> > each bound CXL device. No caller yet; the detection path is added next.
> >
> > Signed-off-by: Manish Honap <[email protected]>
> > ---
> > drivers/vfio/pci/vfio_pci_core.c | 27 +++++++++++++++++++++++++++
> > include/linux/vfio_pci_core.h | 10 ++++++++++
> > 2 files changed, 37 insertions(+)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c
> > b/drivers/vfio/pci/vfio_pci_core.c
> > index 3f11a9624b9c..88e68d43af9a 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -2670,6 +2670,33 @@ static void vfio_pci_dev_set_try_reset(struct
> vfio_device_set *dev_set)
> > }
> > }
> >
> > +static const struct vfio_cxl_ops *vfio_pci_cxl_ops; static
> > +DEFINE_MUTEX(vfio_pci_cxl_ops_lock);
> > +
> > +int vfio_pci_core_register_cxl_ops(const struct vfio_cxl_ops *ops) {
> > + int ret = 0;
> > +
> > + mutex_lock(&vfio_pci_cxl_ops_lock);
> > + if (vfio_pci_cxl_ops)
> > + ret = -EBUSY;
> > + else
> > + vfio_pci_cxl_ops = ops;
> > + mutex_unlock(&vfio_pci_cxl_ops_lock);
> > +
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(vfio_pci_core_register_cxl_ops);
> > +
> > +void vfio_pci_core_unregister_cxl_ops(const struct vfio_cxl_ops *ops)
> > +{
> > + mutex_lock(&vfio_pci_cxl_ops_lock);
> > + if (vfio_pci_cxl_ops == ops)
> > + vfio_pci_cxl_ops = NULL;
> > + mutex_unlock(&vfio_pci_cxl_ops_lock);
> > +}
> > +EXPORT_SYMBOL_GPL(vfio_pci_core_unregister_cxl_ops);
> > +
>
> Use guards to simplify these, especially the registration path where we can
> then
> just return -EBUSY.
>
> I see the get function stores a per-vdev cxl_ops pointer with module reference
> held for the life of the device, so the serialization on the mutex is only
> per-
> device at probe time, but it might still be worthwhile to preempt that with a
> rwsem here where both these paths are writers and the get is a reader.
>
Okay, I will convert register/unregister/get to guards and the mutex to an
rwsem.
(double-register returns -EBUSY)
> > static void vfio_pci_core_cleanup(void) {
> > vfio_pci_uninit_perm_bits();
> > diff --git a/include/linux/vfio_pci_core.h
> > b/include/linux/vfio_pci_core.h index 9a1674c152aa..14753972e714
> > 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_device)(struct vfio_pci_core_device *vdev);
> > + void (*release_device)(struct vfio_pci_core_device *vdev);
> > + /* Pinned per bound CXL device so vfio-cxl cannot unload under usage
> > */
> > + struct module *owner;
> > +};
>
> To mirror vfio_device_ops, should these drop _device and just become .init
> and .release? I think that better reflects their actual usage while the
> eventual
> .open_device and .close_device already reflect the mapping into
> vfio_device_ops sequencing. Thanks,
Okay, I will rename the ops init_device -> .init and release_device -> .release.
Manish
>
> 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,
