PCI/ATS: Use PF PASID for 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, and VFs must not implement
their own PASID Capability.  But commit 751035b ("PCI/ATS: Cache PASID
Capability offset") changed pci_max_pasids() and pci_pasid_features() to
use the PASID Capability of the VF device instead of the associated PF
device.  This leads to IOMMU bind failures when pci_max_pasids() and
pci_pasid_features() are called for VFs.

In pci_max_pasids() and pci_pasid_features(), always use the PF PASID
Capability.

Fixes: 751035b ("PCI/ATS: Cache PASID Capability offset")
Link: https://lore.kernel.org/r/fe891f9755cb18349389609e7fed9940fc5b081a.1580325170.git.sathyanarayanan.kuppuswamy@linux.intel.com
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v5.5+

drivers/pci/ats.c

@@ -424,11 +424,12 @@ void pci_restore_pasid_state(struct pci_dev *pdev)
 int pci_pasid_features(struct pci_dev *pdev)
 {
 	u16 supported;
-	int pasid = pdev->pasid_cap;
+	int pasid;
 
 	if (pdev->is_virtfn)
 		pdev = pci_physfn(pdev);
 
+	pasid = pdev->pasid_cap;
 	if (!pasid)
 		return -EINVAL;
 
@@ -451,11 +452,12 @@ int pci_pasid_features(struct pci_dev *pdev)
 int pci_max_pasids(struct pci_dev *pdev)
 {
 	u16 supported;
-	int pasid = pdev->pasid_cap;
+	int pasid;
 
 	if (pdev->is_virtfn)
 		pdev = pci_physfn(pdev);
 
+	pasid = pdev->pasid_cap;
 	if (!pasid)
 		return -EINVAL;