Re: [PATCH v4 4/4] vfio: pci: Using a device region to retrieve zPCI information

[Cornelia Huck <cohuck@redhat.com>]

On Fri,  6 Sep 2019 20:13:51 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> From: Pierre Morel <pmorel@linux.ibm.com>
> 
> We define a new configuration entry for VFIO/PCI, VFIO_PCI_ZDEV
> 
> When the VFIO_PCI_ZDEV feature is configured we initialize
> a new device region, VFIO_REGION_SUBTYPE_ZDEV_CLP, to hold
> the information from the ZPCI device the use
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
>  drivers/vfio/pci/Kconfig            |  7 +++
>  drivers/vfio/pci/Makefile           |  1 +
>  drivers/vfio/pci/vfio_pci.c         |  9 ++++
>  drivers/vfio/pci/vfio_pci_private.h | 10 +++++
>  drivers/vfio/pci/vfio_pci_zdev.c    | 85 +++++++++++++++++++++++++++++++++++++
>  5 files changed, 112 insertions(+)
>  create mode 100644 drivers/vfio/pci/vfio_pci_zdev.c
> 
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index ac3c1dd..d4562a8 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -45,3 +45,10 @@ config VFIO_PCI_NVLINK2
>  	depends on VFIO_PCI && PPC_POWERNV
>  	help
>  	  VFIO PCI support for P9 Witherspoon machine with NVIDIA V100 GPUs
> +
> +config VFIO_PCI_ZDEV
> +	bool "VFIO PCI Generic for ZPCI devices"
> +	depends on VFIO_PCI && S390
> +	default y
> +	help
> +	  VFIO PCI support for S390 Z-PCI devices

From that description, I'd have no idea whether I'd want that or not.
Is there any downside to enabling it?

> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index f027f8a..781e080 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -3,5 +3,6 @@
>  vfio-pci-y := vfio_pci.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
>  vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
>  vfio-pci-$(CONFIG_VFIO_PCI_NVLINK2) += vfio_pci_nvlink2.o
> +vfio-pci-$(CONFIG_VFIO_PCI_ZDEV) += vfio_pci_zdev.o
>  
>  obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 703948c..b40544a 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -356,6 +356,15 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
>  		}
>  	}
>  
> +	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV)) {
> +		ret = vfio_pci_zdev_init(vdev);
> +		if (ret) {
> +			dev_warn(&vdev->pdev->dev,
> +				 "Failed to setup ZDEV regions\n");
> +			goto disable_exit;
> +		}
> +	}
> +
>  	vfio_pci_probe_mmaps(vdev);
>  
>  	return 0;
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index ee6ee91..08e02f5 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -186,4 +186,14 @@ static inline int vfio_pci_ibm_npu2_init(struct vfio_pci_device *vdev)
>  	return -ENODEV;
>  }
>  #endif
> +
> +#ifdef CONFIG_VFIO_PCI_ZDEV
> +extern int vfio_pci_zdev_init(struct vfio_pci_device *vdev);
> +#else
> +static inline int vfio_pci_zdev_init(struct vfio_pci_device *vdev)
> +{
> +	return -ENODEV;

If you really want to have this configurable, why not just return 0
here and skip the IS_ENABLED check above?

> +}
> +#endif
> +
>  #endif /* VFIO_PCI_PRIVATE_H */

(...)
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