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

[Matthew Rosato]

On 9/22/20 7:22 AM, Cornelia Huck wrote:
> On Sat, 19 Sep 2020 11:28:38 -0400
> Matthew Rosato <mjrosato@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > ---
> >   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;
> > +}