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

Matthew Rosato
2019-09-19T20:57:28Z

On 9/19/19 11:25 AM, Cornelia Huck wrote:
> 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?
>

:) Not really, you're just getting information from the hardware vs
using hard-coded defaults. The only reason I could think of to turn it
off would be if you wanted/needed to restore this hard-coded behavior.

bool "VFIO PCI support for generic ZPCI devices" ?

"Support for sharing ZPCI hardware device information between the host
and guests." ?

>> 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?
>

I agree that it functionally has the same result, but in this case I
think Pierre was repeating the same thing the other init() functions
here (IGD, etc) are doing. Though I guess the other cases have at least
1 other condition they care about besides IS_ENABLED... OK, I can make
this change.

>> +}
>> +#endif
>> +
>> #endif /* VFIO_PCI_PRIVATE_H */
>
> (...)
>