Re: [PATCH 4/4] vfio-pci/zdev: use a device region to retrieve zPCI information

Matthew Rosato
2020-09-22T14:02:53Z

On 9/22/20 7:22 AM, Cornelia Huck wrote:
> On Sat, 19 Sep 2020 11:28:38 -0400
> Matthew Rosato <mjrosato@linux.ibm.com> wrote:
>
>> Define a new configuration entry VFIO_PCI_ZDEV for VFIO/PCI.
>>
>> When this s390-only feature is configured we initialize a new device
>> region, VFIO_REGION_SUBTYPE_IBM_ZPCI_CLP, to hold information provided
>> by the underlying hardware.
>>
>> This patch is based on work previously done by Pierre Morel.
>>
>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
>> ---
>> drivers/vfio/pci/Kconfig | 13 ++
>> drivers/vfio/pci/Makefile | 1 +
>> drivers/vfio/pci/vfio_pci.c | 8 ++
>> drivers/vfio/pci/vfio_pci_private.h | 10 ++
>> drivers/vfio/pci/vfio_pci_zdev.c | 242 ++++++++++++++++++++++++++++++++++++
>
> Maybe you want to add yourself to MAINTAINERS for the zdev-specific
> files? You're probably better suited to review changes to the
> zpci-specific code :)

Of course, will do. Looking at how we split vfio-ap and vfio-ccw, I'll
add an S390 VFIO-PCI DRIVER category and point to the new .h and .c file
for now.

>
>> 5 files changed, 274 insertions(+)
>> create mode 100644 drivers/vfio/pci/vfio_pci_zdev.c
>
> (...)
>
>> +int vfio_pci_zdev_init(struct vfio_pci_device *vdev)
>> +{
>> + struct vfio_region_zpci_info *region;
>> + struct zpci_dev *zdev;
>> + size_t clp_offset;
>> + int size;
>> + int ret;
>> +
>> + if (!vdev->pdev->bus)
>> + return -ENODEV;
>> +
>> + zdev = to_zpci(vdev->pdev);
>> + if (!zdev)
>> + return -ENODEV;
>> +
>> + /* Calculate size needed for all supported CLP features */
>> + size = sizeof(*region) +
>> + sizeof(struct vfio_region_zpci_info_qpci) +
>> + sizeof(struct vfio_region_zpci_info_qpcifg) +
>> + (sizeof(struct vfio_region_zpci_info_util) + CLP_UTIL_STR_LEN) +
>> + (sizeof(struct vfio_region_zpci_info_pfip) +
>> + CLP_PFIP_NR_SEGMENTS);
>> +
>> + region = kmalloc(size, GFP_KERNEL);
>> + if (!region)
>> + return -ENOMEM;
>> +
>> + /* Fill in header */
>> + region->argsz = size;
>> + clp_offset = region->offset = sizeof(struct vfio_region_zpci_info);
>> +
>> + /* Fill the supported CLP features */
>> + clp_offset = vfio_pci_zdev_add_qpci(zdev, region, clp_offset);
>> + clp_offset = vfio_pci_zdev_add_qpcifg(zdev, region, clp_offset);
>> + clp_offset = vfio_pci_zdev_add_util(zdev, region, clp_offset);
>> + clp_offset = vfio_pci_zdev_add_pfip(zdev, region, clp_offset);
>
> So, the regions are populated once. Can any of the values in the
> hardware structures be modified by a guest? Or changed from the
> hardware side?
>

The region is created read-only (vfio_pci_zdev_rw returns -EINVAL on
writes), so no guest modification. The expectation is the guest can
read the region and take what it wants / ignore what it doesn't.

The CLPs covered by this region are not intended to change once the
device is up.

If we end up needing either of the above for a different CLP, I would
think an additional/different region would be appropriate.

>> +
>> + ret = vfio_pci_register_dev_region(vdev,
>> + PCI_VENDOR_ID_IBM | VFIO_REGION_TYPE_PCI_VENDOR_TYPE,
>> + VFIO_REGION_SUBTYPE_IBM_ZPCI_CLP, &vfio_pci_zdev_regops,
>> + size, VFIO_REGION_INFO_FLAG_READ, region);
>> + if (ret)
>> + kfree(region);
>> +
>> + return ret;
>> +}
>