PCI/ATS: Handle sharing of PF PASID Capability with all VFs

Per PCIe r5.0, sec 9.3.7.14, if a PF implements the PASID Capability, the
PF PASID configuration is shared by its VFs.  VFs must not implement their
own PASID Capability.  Since VFs don't have a PASID Capability,
pci_enable_pasid() always failed, which caused IOMMU setup to fail.

Update the PASID interfaces so for VFs they reflect the state of the PF
PASID.

[bhelgaas: rebase without pasid_cap caching, commit log]
Suggested-by: Ashok Raj <ashok.raj@intel.com>
Link: https://lore.kernel.org/r/8ba1ac192e4ac737508b6ac15002158e176bab91.1567029860.git.sathyanarayanan.kuppuswamy@linux.intel.com
Link: https://lore.kernel.org/r/20190905193146.90250-3-helgaas@kernel.orgSigned-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Keith Busch <keith.busch@intel.com>

drivers/pci/ats.c

@@ -346,6 +346,16 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
 	u16 control, supported;
 	int pos;
 
+	/*
+	 * VFs must not implement the PASID Capability, but if a PF
+	 * supports PASID, its VFs share the PF PASID configuration.
+	 */
+	if (pdev->is_virtfn) {
+		if (pci_physfn(pdev)->pasid_enabled)
+			return 0;
+		return -EINVAL;
+	}
+
 	if (WARN_ON(pdev->pasid_enabled))
 		return -EBUSY;
 
@@ -383,6 +393,10 @@ void pci_disable_pasid(struct pci_dev *pdev)
 	u16 control = 0;
 	int pos;
 
+	/* VFs share the PF PASID configuration */
+	if (pdev->is_virtfn)
+		return;
+
 	if (WARN_ON(!pdev->pasid_enabled))
 		return;
 
@@ -405,6 +419,9 @@ void pci_restore_pasid_state(struct pci_dev *pdev)
 	u16 control;
 	int pos;
 
+	if (pdev->is_virtfn)
+		return;
+
 	if (!pdev->pasid_enabled)
 		return;
 
@@ -432,6 +449,9 @@ int pci_pasid_features(struct pci_dev *pdev)
 	u16 supported;
 	int pos;
 
+	if (pdev->is_virtfn)
+		pdev = pci_physfn(pdev);
+
 	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
 	if (!pos)
 		return -EINVAL;
@@ -458,6 +478,9 @@ int pci_max_pasids(struct pci_dev *pdev)
 	u16 supported;
 	int pos;
 
+	if (pdev->is_virtfn)
+		pdev = pci_physfn(pdev);
+
 	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
 	if (!pos)
 		return -EINVAL;