Re: [PATCH 3/3] vfio: Report PASID capability via VFIO_DEVICE_FEATURE ioctl

Yi Liu
2023-12-11T08:05:44Z

On 2023/12/7 16:47, Tian, Kevin wrote:
>> From: Liu, Yi L <yi.l.liu@intel.com>
>> Sent: Monday, November 27, 2023 2:39 PM
>>
>> +static int vfio_pci_core_feature_pasid(struct vfio_device *device, u32 flags,
>> + struct vfio_device_feature_pasid __user
>> *arg,
>> + size_t argsz)
>> +{
>> + struct vfio_pci_core_device *vdev =
>> + container_of(device, struct vfio_pci_core_device, vdev);
>> + struct vfio_device_feature_pasid pasid = { 0 };
>> + struct pci_dev *pdev = vdev->pdev;
>> + u32 capabilities = 0;
>> + int ret;
>> +
>> + /* We do not support SET of the PASID capability */
>
> this line alone is meaningless. Please explain the reason e.g. due to
> no PASID capability per VF...

sure. I think the major reason is we don't allow userspace to change the
PASID configuration. is it?

>
>> + ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
>> + sizeof(pasid));
>> + if (ret != 1)
>> + return ret;
>> +
>> + /*
>> + * Needs go to PF if the device is VF as VF shares its PF's
>> + * PASID Capability.
>> + */
>
> /* VF shares the PASID capability of its PF */

got it.

>> + if (pdev->is_virtfn)
>> + pdev = pci_physfn(pdev);
>> +
>> + if (!pdev->pasid_enabled)
>> + goto out;
>> +
>> +#ifdef CONFIG_PCI_PASID
>> + pci_read_config_dword(pdev, pdev->pasid_cap + PCI_PASID_CAP,
>> + &capabilities);
>> +#endif
>
> #ifdef is unnecessary. If CONFIG_PCI_PASID is false pdev->pasid_enabled
> won't be set anyway.

it's sad that the pdev->pasid_cap is defined under #if CONFIG_PCI_PASID.
Perhaps we can have a wrapper for it.

> and it should read from PCI_PASID_CTRL which indicates whether a
> capability is actually enabled.

yes, for the EXEC and PRIV capability, needs to check if it's enabled or
not before reporting.

>
>> +/**
>> + * Upon VFIO_DEVICE_FEATURE_GET, return the PASID capability for the
>> device.
>> + * Zero width means no support for PASID.
>
> also mention the encoding of this field according to PCIe spec.

yes.

> or turn it to a plain number field.

It is not exact the same as the spec since bit0 is reserved. But
here bit0 is used as well.

>> + */
>> +struct vfio_device_feature_pasid {
>> + __u16 capabilities;
>> +#define VFIO_DEVICE_PASID_CAP_EXEC (1 << 0)
>> +#define VFIO_DEVICE_PASID_CAP_PRIV (1 << 1)
>> + __u8 width;
>> + __u8 __reserved;
>> +};
>> +#define VFIO_DEVICE_FEATURE_PASID 11
>> +
>> /* -------- API for Type1 VFIO IOMMU -------- */
>>
>> /**
>> --
>> 2.34.1
>

--
Regards,
Yi Liu