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

[Yi Liu]

On 2023/12/7 16:47, Tian, Kevin wrote:
> > From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> > 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