vfio/pci: Mask buggy SR-IOV VF INTx support

The SR-IOV spec requires that VFs must report zero for the INTx pin
register as VFs are precluded from INTx support.  It's much easier for
the host kernel to understand whether a device is a VF and therefore
whether a non-zero pin register value is bogus than it is to do the
same in userspace.  Override the INTx count for such devices and
virtualize the pin register to provide a consistent view of the device
to the user.

As this is clearly a spec violation, warn about it to support hardware
validation, but also provide a known whitelist as it doesn't do much
good to continue complaining if the hardware vendor doesn't plan to
fix it.

Known devices with this issue: 8086:270c

Tested-by: Gage Eads <gage.eads@intel.com>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci.c

@@ -434,10 +434,14 @@ static int vfio_pci_get_irq_count(struct vfio_pci_device *vdev, int irq_type)
 {
 	if (irq_type == VFIO_PCI_INTX_IRQ_INDEX) {
 		u8 pin;
+
+		if (!IS_ENABLED(CONFIG_VFIO_PCI_INTX) ||
+		    vdev->nointx || vdev->pdev->is_virtfn)
+			return 0;
+
 		pci_read_config_byte(vdev->pdev, PCI_INTERRUPT_PIN, &pin);
-		if (IS_ENABLED(CONFIG_VFIO_PCI_INTX) && !vdev->nointx && pin)
-			return 1;
 
+		return pin ? 1 : 0;
 	} else if (irq_type == VFIO_PCI_MSI_IRQ_INDEX) {
 		u8 pos;
 		u16 flags;

drivers/vfio/pci/vfio_pci_config.c

@@ -1611,6 +1611,15 @@ static int vfio_ecap_init(struct vfio_pci_device *vdev)
 	return 0;
 }
 
+/*
+ * Nag about hardware bugs, hopefully to have vendors fix them, but at least
+ * to collect a list of dependencies for the VF INTx pin quirk below.
+ */
+static const struct pci_device_id known_bogus_vf_intx_pin[] = {
+	{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x270c) },
+	{}
+};
+
 /*
  * For each device we allocate a pci_config_map that indicates the
  * capability occupying each dword and thus the struct perm_bits we
@@ -1676,6 +1685,24 @@ int vfio_config_init(struct vfio_pci_device *vdev)
 	if (pdev->is_virtfn) {
 		*(__le16 *)&vconfig[PCI_VENDOR_ID] = cpu_to_le16(pdev->vendor);
 		*(__le16 *)&vconfig[PCI_DEVICE_ID] = cpu_to_le16(pdev->device);
+
+		/*
+		 * Per SR-IOV spec rev 1.1, 3.4.1.18 the interrupt pin register
+		 * does not apply to VFs and VFs must implement this register
+		 * as read-only with value zero.  Userspace is not readily able
+		 * to identify whether a device is a VF and thus that the pin
+		 * definition on the device is bogus should it violate this
+		 * requirement.  We already virtualize the pin register for
+		 * other purposes, so we simply need to replace the bogus value
+		 * and consider VFs when we determine INTx IRQ count.
+		 */
+		if (vconfig[PCI_INTERRUPT_PIN] &&
+		    !pci_match_id(known_bogus_vf_intx_pin, pdev))
+			pci_warn(pdev,
+				 "Hardware bug: VF reports bogus INTx pin %d\n",
+				 vconfig[PCI_INTERRUPT_PIN]);
+
+		vconfig[PCI_INTERRUPT_PIN] = 0; /* Gratuitous for good VFs */
 	}
 
 	if (!IS_ENABLED(CONFIG_VFIO_PCI_INTX) || vdev->nointx)