Since commit 25f39d3dcb48 ("s390/pci: Ignore RID for isolated VFs") PFs
which are not initially configured but in standby are considered
isolated. That is they create only a single function PCI domain. Due to
the PCI domains being created on discovery, this means that even if they
are configured later on, sibling PFs and their child VFs will not be
added to their PCI domain breaking SR-IOV expectations.
The reason the referenced commit ignored standby PFs for the creation of
multi-function PCI subhierarchies, was to work around a PCI domain
renumbering scenario on reboot. The renumbering would occur after
removing a previously in standby PF, whose domain number is used for its
configured sibling PFs and their child VFs, but which itself remained in
standby. When this is followed by a reboot, the sibling PF is used
instead to determine the PCI domain number of it and its child VFs.
In principle it is not possible to know which standby PFs will be
configured later and which may be removed. The PCI domain and root bus
are pre-requisites for hotplug slots so the decision of which functions
belong to which domain can not be postponed. With the renumbering
occurring only in rare circumstances and being generally benign, accept
it as an oddity and fix SR-IOV for initially standby PFs simply by
allowing them to create PCI domains.
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Gerd Bayer <gbayer@xxxxxxxxxxxxx>
Fixes: 25f39d3dcb48 ("s390/pci: Ignore RID for isolated VFs")
Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
---
Changes in v3:
- Add R-b from Gerd
- Add Cc: stable…
- Add commas (Sandy)
Changes in v2:
- Reword commit message
---
arch/s390/pci/pci_bus.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/arch/s390/pci/pci_bus.c b/arch/s390/pci/pci_bus.c
index d5ace00d10f04285f899284481f1e426187d4ff4..857afbc4828f0c677f88cc80dd4a5fff104a615a 100644
--- a/arch/s390/pci/pci_bus.c
+++ b/arch/s390/pci/pci_bus.c
@@ -171,7 +171,6 @@ void zpci_bus_scan_busses(void)
static bool zpci_bus_is_multifunction_root(struct zpci_dev *zdev)
{
return !s390_pci_no_rid && zdev->rid_available &&
- zpci_is_device_configured(zdev) &&
!zdev->vfn;
}
---
base-commit: 6b7afe1a2b6905e42fe45bd7015f20baa856e28e
change-id: 20250116-fix_standby_pf-e1d51394e9b3
Best regards,
--
Niklas Schnelle
