s390/pci: Fix zpci_bus_is_isolated_vf() for non-VFs

JIRA: https://issues.redhat.com/browse/RHEL-88818

commit 8691abd
Author: Niklas Schnelle <schnelle@linux.ibm.com>
Date:   Thu Mar 20 17:26:12 2025 +0100

    s390/pci: Fix zpci_bus_is_isolated_vf() for non-VFs

    For non-VFs, zpci_bus_is_isolated_vf() should return false because they
    aren't VFs. While zpci_iov_find_parent_pf() specifically checks if
    a function is a VF, it then simply returns that there is no parent. The
    simplistic check for a parent then leads to these functions being
    confused with isolated VFs and isolating them on their own domain even
    if sibling PFs should share the domain.

    Fix this by explicitly checking if a function is not a VF. Note also
    that at this point the case where RIDs are ignored is already handled
    and in this case all PCI functions get isolated by being detected in
    zpci_bus_is_multifunction_root().

    Cc: stable@vger.kernel.org
    Fixes: 2844ddb ("s390/pci: Fix handling of isolated VFs")
    Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
    Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
    Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Signed-off-by: Mete Durlu <mdurlu@redhat.com>

Author: Mete Durlu

arch/s390/pci/pci_bus.c

@@ -335,6 +335,9 @@ static bool zpci_bus_is_isolated_vf(struct zpci_bus *zbus, struct zpci_dev *zdev
 {
 	struct pci_dev *pdev;
 
+	if (!zdev->vfn)
+		return false;
+
 	pdev = zpci_iov_find_parent_pf(zbus, zdev);
 	if (!pdev)
 		return true;