On Wed, 2025-10-22 at 14:24 -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.
I wonder if LoongArch which now also does per PCI function pass-through might need this too. Adding their KVM maintainers.
Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") Cc: stable@vger.kernel.org Suggested-by: Niklas Schnelle schnelle@linux.ibm.com Signed-off-by: Farhan Ali alifm@linux.ibm.com
drivers/pci/pci.c | 5 +++-- drivers/pci/slot.c | 25 ++++++++++++++++++++++--- include/linux/pci.h | 1 + 3 files changed, 26 insertions(+), 5 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index b14dd064006c..36ee38e0d817 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -4980,8 +4980,9 @@ static int pci_reset_hotplug_slot(struct hotplug_slot *hotplug, bool probe) static int pci_dev_reset_slot_function(struct pci_dev *dev, bool probe) {
- if (dev->multifunction || dev->subordinate || !dev->slot ||
dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET)
- if (dev->subordinate || !dev->slot ||
dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||(dev->multifunction && !dev->slot->per_func_slot))return pci_reset_hotplug_slot(dev->slot->hotplug, probe); diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c index 50fb3eb595fe..ed10fa3ae727 100644 --- a/drivers/pci/slot.c +++ b/drivers/pci/slot.c @@ -63,6 +63,22 @@ static ssize_t cur_speed_read_file(struct pci_slot *slot, char *buf) return bus_speed_read(slot->bus->cur_bus_speed, buf); } +static bool pci_dev_matches_slot(struct pci_dev *dev, struct pci_slot *slot) +{
- if (slot->per_func_slot)
return dev->devfn == slot->number;- return PCI_SLOT(dev->devfn) == slot->number;
+}
+static bool pci_slot_enabled_per_func(void) +{
- if (IS_ENABLED(CONFIG_S390))
return true;- return false;
+}
--- snip ---
diff --git a/include/linux/pci.h b/include/linux/pci.h index d1fdf81fbe1e..6ad194597ab5 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -78,6 +78,7 @@ struct pci_slot { struct list_head list; /* Node in list of slots */ struct hotplug_slot *hotplug; /* Hotplug info (move here) */ unsigned char number; /* PCI_SLOT(pci_dev->devfn) */
- unsigned int per_func_slot:1; /* Allow per function slot */ struct kobject kobj;
};
Reviewed-by: Niklas Schnelle schnelle@linux.ibm.com