vfio/pci: Handle INTx IRQ_NOTCONNECTED

JIRA: https://issues.redhat.com/browse/RHEL-85587
JIRA: https://issues.redhat.com/browse/RHEL-85591

commit 860be25
Author: Alex Williamson <alex.williamson@redhat.com>
Date:   Tue Mar 11 17:06:21 2025 -0600

    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>

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: Alex Williamson

drivers/vfio/pci/vfio_pci_config.c

@@ -1813,7 +1813,8 @@ 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));