On Mon, 2025-10-20 at 12:01 -0700, Farhan Ali wrote:
On s390 systems, which use a machine level hypervisor, PCI devices are always accessed through a form of PCI pass-through which fundamentally operates on a per PCI function granularity. This is also reflected in the s390 PCI hotplug driver which creates hotplug slots for individual PCI functions. Its reset_slot() function, which is a wrapper for zpci_hot_reset_device(), thus also resets individual functions.
Currently, the kernel's PCI_SLOT() macro assigns the same pci_slot object to multifunction devices. This approach worked fine on s390 systems that only exposed virtual functions as individual PCI domains to the operating system. Since commit 44510d6fa0c0 ("s390/pci: Handling multifunctions") s390 supports exposing the topology of multifunction PCI devices by grouping them in a shared PCI domain. When attempting to reset a function through the hotplug driver, the shared slot assignment causes the wrong function to be reset instead of the intended one. It also leaks memory as we do create a pci_slot object for the function, but don't correctly free it in pci_slot_release().
Add a flag for struct pci_slot to allow per function PCI slots for functions managed through a hypervisor, which exposes individual PCI functions while retaining the topology.
Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") Cc: stable@vger.kernel.org Suggested-by: Niklas Schnelle schnelle@linux.ibm.com Reviewed-by: Benjamin Block bblock@linux.ibm.com Signed-off-by: Farhan Ali alifm@linux.ibm.com
drivers/pci/hotplug/s390_pci_hpc.c | 10 ++++++++-- drivers/pci/pci.c | 5 +++-- drivers/pci/slot.c | 14 +++++++++++--- include/linux/pci.h | 1 + 4 files changed, 23 insertions(+), 7 deletions(-)
diff --git a/drivers/pci/hotplug/s390_pci_hpc.c b/drivers/pci/hotplug/s390_pci_hpc.c index d9996516f49e..8b547de464bf 100644 --- a/drivers/pci/hotplug/s390_pci_hpc.c +++ b/drivers/pci/hotplug/s390_pci_hpc.c @@ -126,14 +126,20 @@ static const struct hotplug_slot_ops s390_hotplug_slot_ops = { int zpci_init_slot(struct zpci_dev *zdev) {
- int ret; char name[SLOT_NAME_SIZE]; struct zpci_bus *zbus = zdev->zbus;
zdev->hotplug_slot.ops = &s390_hotplug_slot_ops; snprintf(name, SLOT_NAME_SIZE, "%08x", zdev->fid);
- return pci_hp_register(&zdev->hotplug_slot, zbus->bus,
zdev->devfn, name);
- ret = pci_hp_register(&zdev->hotplug_slot, zbus->bus,
zdev->devfn, name);- if (ret)
return ret;- zdev->hotplug_slot.pci_slot->per_func_slot = 1;
I think the way this works is a bit odd. Due to the order of setting the flag pci_create_slot() in pci_hp_register() tries to match using the wrong per_func_slot == 0. This doesn't really cause mismatches though because the slot->number won't match the PCI_SLOT(dev->devfn) except for the slot->number 0 where it is fine.
One way to improve(?) on this is to have a per_func_slot flag also in the struct hotplug_slot and then copy it over into the newly created struct pci_slot. But then we have this flag twice. Or maybe this really should be an argument to pci_create_slot()?