From dcc5bec09e23bbc4f9de055a11fce9937244f2c8 Mon Sep 17 00:00:00 2001 From: Farhan Ali Date: Wed, 5 Aug 2026 09:55:15 -0700 Subject: PCI: Allow per function PCI slots to fix slot reset on s390 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 pci_create_slot() 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. This creates a problem when resetting a function through the hotplug driver's slot_reset() interface. 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. Since we can use all 8 bits for slot 'number' (for ARI devices), change slot 'number' u16 to account for special values PCI_SLOT_PLACEHOLDER and PCI_SLOT_ALL_DEVICES. Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") Suggested-by: Niklas Schnelle Signed-off-by: Farhan Ali Signed-off-by: Bjorn Helgaas Reviewed-by: Niklas Schnelle Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260805165518.794-3-alifm@linux.ibm.com --- drivers/pci/pci.c | 5 +++-- drivers/pci/slot.c | 29 +++++++++++++++++++++++------ include/linux/pci.h | 7 ++++--- 3 files changed, 30 insertions(+), 11 deletions(-) diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 77b17b13ee61..350bae907ebf 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -4897,8 +4897,9 @@ 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 -ENOTTY; return pci_reset_hotplug_slot(dev->slot->hotplug, probe); diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c index 42ff66461f74..897223f01f6a 100644 --- a/drivers/pci/slot.c +++ b/drivers/pci/slot.c @@ -72,6 +72,23 @@ 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 slot->number == PCI_SLOT_ALL_DEVICES || + PCI_SLOT(dev->devfn) == slot->number; +} + +static bool pci_slot_enabled_per_func(void) +{ + if (IS_ENABLED(CONFIG_S390)) + return true; + + return false; +} + static void pci_slot_release(struct kobject *kobj) { struct pci_dev *dev; @@ -82,8 +99,7 @@ static void pci_slot_release(struct kobject *kobj) down_read(&pci_bus_sem); list_for_each_entry(dev, &slot->bus->devices, bus_list) - if (slot->number == PCI_SLOT_ALL_DEVICES || - PCI_SLOT(dev->devfn) == slot->number) + if (pci_dev_matches_slot(dev, slot)) dev->slot = NULL; up_read(&pci_bus_sem); @@ -187,8 +203,7 @@ void pci_dev_assign_slot(struct pci_dev *dev) mutex_lock(&pci_slot_mutex); list_for_each_entry(slot, &dev->bus->slots, list) - if (slot->number == PCI_SLOT_ALL_DEVICES || - PCI_SLOT(dev->devfn) == slot->number) + if (pci_dev_matches_slot(dev, slot)) dev->slot = slot; mutex_unlock(&pci_slot_mutex); } @@ -299,6 +314,9 @@ placeholder: slot->bus = pci_bus_get(parent); slot->number = slot_nr; + if (pci_slot_enabled_per_func()) + slot->per_func_slot = 1; + slot->kobj.kset = pci_slots_kset; slot_name = make_slot_name(name); @@ -319,8 +337,7 @@ placeholder: down_read(&pci_bus_sem); list_for_each_entry(dev, &parent->devices, bus_list) - if (slot_nr == PCI_SLOT_ALL_DEVICES || - PCI_SLOT(dev->devfn) == slot_nr) + if (pci_dev_matches_slot(dev, slot)) dev->slot = slot; up_read(&pci_bus_sem); diff --git a/include/linux/pci.h b/include/linux/pci.h index 3824a8dd551e..8593384489db 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -79,17 +79,18 @@ * and, if ARI Forwarding is enabled, functions may appear to be on multiple * devices. */ -#define PCI_SLOT_ALL_DEVICES 0xfe +#define PCI_SLOT_ALL_DEVICES 0xfeff /* Used to identify a slot as a placeholder */ -#define PCI_SLOT_PLACEHOLDER 0xff +#define PCI_SLOT_PLACEHOLDER 0xffff /* pci_slot represents a physical slot */ struct pci_slot { struct pci_bus *bus; /* Bus this slot is on */ struct list_head list; /* Node in list of slots */ struct hotplug_slot *hotplug; /* Hotplug info (move here) */ - unsigned char number; /* Device nr, or PCI_SLOT_ALL_DEVICES */ + u16 number; /* Device nr, or PCI_SLOT_ALL_DEVICES */ + unsigned int per_func_slot:1; /* Allow per function slot */ struct kobject kobj; }; -- cgit v1.2.3