vfio/pci: Handle INTx IRQ_NOTCONNECTED

Some systems report INTx as not routed by setting pdev->irq to
IRQ_NOTCONNECTED, resulting in a -ENOTCONN error when trying to
setup eventfd signaling.  Include this in the set of conditions
for which the PIN register is virtualized to zero.

Additionally consolidate vfio_pci_get_irq_count() to use this
virtualized value in reporting INTx support via ioctl and sanity
checking ioctl paths since pdev->irq is re-used when the device
is in MSI mode.

The combination of these results in both the config space of the
device and the ioctl interface behaving as if the device does not
support INTx.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20250311230623.1264283-1-alex.williamson@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: awilliam

drivers/vfio/pci/vfio_pci_config.c

@@ -1814,7 +1814,8 @@ int vfio_config_init(struct vfio_pci_core_device *vdev)
 					cpu_to_le16(PCI_COMMAND_MEMORY);
 	}
 
-	if (!IS_ENABLED(CONFIG_VFIO_PCI_INTX) || vdev->nointx)
+	if (!IS_ENABLED(CONFIG_VFIO_PCI_INTX) || vdev->nointx ||
+	    vdev->pdev->irq == IRQ_NOTCONNECTED)
 		vconfig[PCI_INTERRUPT_PIN] = 0;
 
 	ret = vfio_cap_init(vdev);

drivers/vfio/pci/vfio_pci_core.c

@@ -727,15 +727,7 @@ EXPORT_SYMBOL_GPL(vfio_pci_core_finish_enable);
 static int vfio_pci_get_irq_count(struct vfio_pci_core_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);
-
-		return pin ? 1 : 0;
+		return vdev->vconfig[PCI_INTERRUPT_PIN] ? 1 : 0;
 	} else if (irq_type == VFIO_PCI_MSI_IRQ_INDEX) {
 		u8 pos;
 		u16 flags;

drivers/vfio/pci/vfio_pci_intrs.c

@@ -259,7 +259,7 @@ static int vfio_intx_enable(struct vfio_pci_core_device *vdev,
 	if (!is_irq_none(vdev))
 		return -EINVAL;
 
-	if (!pdev->irq)
+	if (!pdev->irq || pdev->irq == IRQ_NOTCONNECTED)
 		return -ENODEV;
 
 	name = kasprintf(GFP_KERNEL_ACCOUNT, "vfio-intx(%s)", pci_name(pdev));