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

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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




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