* [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 [not found] <20260421163031.704-1-alifm@linux.ibm.com> @ 2026-04-21 16:30 ` Farhan Ali 2026-05-04 15:52 ` Gerd Bayer 0 siblings, 1 reply; 4+ messages in thread From: Farhan Ali @ 2026-04-21 16:30 UTC (permalink / raw) To: linux-s390, linux-kernel, linux-pci Cc: helgaas, lukas, alex, clg, alifm, schnelle, mjrosato, stable 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. 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 -1 and PCI_SLOT_ALL_DEVICES. Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") Cc: stable@vger.kernel.org Suggested-by: Niklas Schnelle <schnelle@linux.ibm.com> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com> Signed-off-by: Farhan Ali <alifm@linux.ibm.com> --- drivers/pci/hotplug/rpaphp_slot.c | 2 +- drivers/pci/pci.c | 5 +++-- drivers/pci/slot.c | 33 +++++++++++++++++++++++-------- include/linux/pci.h | 8 ++++++-- 4 files changed, 35 insertions(+), 13 deletions(-) diff --git a/drivers/pci/hotplug/rpaphp_slot.c b/drivers/pci/hotplug/rpaphp_slot.c index 67362e5b9971..92eabf5f61b9 100644 --- a/drivers/pci/hotplug/rpaphp_slot.c +++ b/drivers/pci/hotplug/rpaphp_slot.c @@ -84,7 +84,7 @@ int rpaphp_register_slot(struct slot *slot) struct hotplug_slot *php_slot = &slot->hotplug_slot; u32 my_index; int retval; - int slotno = -1; + int slotno = PCI_SLOT_PLACEHOLDER; dbg("%s registering slot:path[%pOF] index[%x], name[%s] pdomain[%x] type[%d]\n", __func__, slot->dn, slot->index, slot->name, diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 8f7cfcc00090..d0c9f0166af5 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -4865,8 +4865,9 @@ 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 e0b7fb43423c..3f6e5dce27a0 100644 --- a/drivers/pci/slot.c +++ b/drivers/pci/slot.c @@ -37,7 +37,7 @@ static const struct sysfs_ops pci_slot_sysfs_ops = { static ssize_t address_read_file(struct pci_slot *slot, char *buf) { - if (slot->number == 0xff) + if (slot->number == (u16)PCI_SLOT_PLACEHOLDER) return sysfs_emit(buf, "%04x:%02x\n", pci_domain_nr(slot->bus), slot->bus->number); @@ -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); @@ -176,8 +192,7 @@ 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); } @@ -256,7 +271,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, mutex_lock(&pci_slot_mutex); - if (slot_nr == -1) + if (slot_nr == PCI_SLOT_PLACEHOLDER) goto placeholder; /* @@ -287,6 +302,9 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, 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); @@ -307,8 +325,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, 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 2c4454583c11..d58982aa8730 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -78,14 +78,18 @@ * 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 -1 /* 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; }; -- 2.43.0 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 2026-04-21 16:30 ` [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 Farhan Ali @ 2026-05-04 15:52 ` Gerd Bayer 2026-05-04 17:00 ` Farhan Ali 0 siblings, 1 reply; 4+ messages in thread From: Gerd Bayer @ 2026-05-04 15:52 UTC (permalink / raw) To: Farhan Ali, linux-s390, linux-kernel, linux-pci Cc: helgaas, lukas, alex, clg, schnelle, mjrosato, stable On Tue, 2026-04-21 at 09:30 -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. 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(). > Hi Farhan, sorry for jumping this late into reviewing this, but I think I'd prefer a different approach than extending the slot member to u16 to make the full range of 256 usable: > 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 -1 and PCI_SLOT_ALL_DEVICES. > > Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") > Cc: stable@vger.kernel.org > Suggested-by: Niklas Schnelle <schnelle@linux.ibm.com> > Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com> > Signed-off-by: Farhan Ali <alifm@linux.ibm.com> > --- > drivers/pci/hotplug/rpaphp_slot.c | 2 +- > drivers/pci/pci.c | 5 +++-- > drivers/pci/slot.c | 33 +++++++++++++++++++++++-------- > include/linux/pci.h | 8 ++++++-- > 4 files changed, 35 insertions(+), 13 deletions(-) > > diff --git a/drivers/pci/hotplug/rpaphp_slot.c b/drivers/pci/hotplug/rpaphp_slot.c > index 67362e5b9971..92eabf5f61b9 100644 > --- a/drivers/pci/hotplug/rpaphp_slot.c > +++ b/drivers/pci/hotplug/rpaphp_slot.c > @@ -84,7 +84,7 @@ int rpaphp_register_slot(struct slot *slot) > struct hotplug_slot *php_slot = &slot->hotplug_slot; > u32 my_index; > int retval; > - int slotno = -1; > + int slotno = PCI_SLOT_PLACEHOLDER; > > dbg("%s registering slot:path[%pOF] index[%x], name[%s] pdomain[%x] type[%d]\n", > __func__, slot->dn, slot->index, slot->name, > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index 8f7cfcc00090..d0c9f0166af5 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -4865,8 +4865,9 @@ 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 e0b7fb43423c..3f6e5dce27a0 100644 > --- a/drivers/pci/slot.c > +++ b/drivers/pci/slot.c > @@ -37,7 +37,7 @@ static const struct sysfs_ops pci_slot_sysfs_ops = { > > static ssize_t address_read_file(struct pci_slot *slot, char *buf) > { > - if (slot->number == 0xff) > + if (slot->number == (u16)PCI_SLOT_PLACEHOLDER) > return sysfs_emit(buf, "%04x:%02x\n", > pci_domain_nr(slot->bus), > slot->bus->number); > @@ -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); > > @@ -176,8 +192,7 @@ 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); > } > @@ -256,7 +271,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, > > mutex_lock(&pci_slot_mutex); > > - if (slot_nr == -1) > + if (slot_nr == PCI_SLOT_PLACEHOLDER) > goto placeholder; > > /* > @@ -287,6 +302,9 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, > 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); > @@ -307,8 +325,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, > > 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 2c4454583c11..d58982aa8730 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -78,14 +78,18 @@ > * 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 -1 > > /* 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 */ How about you introduce two additional single-bit flag members here for - placeholder, and - slot_all_devices and avoid creating an artifically wide number member. Eventually, this means that the special cases "placeholder-slot" and "bus-wide slot" should be broken out of pci_create_slot(). > struct kobject kobj; > }; > Hope this makes any sense? It almost makes me wonder if this should be handled with a pre-cursor patch to this... Thanks, Gerd ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 2026-05-04 15:52 ` Gerd Bayer @ 2026-05-04 17:00 ` Farhan Ali 2026-05-06 11:55 ` Gerd Bayer 0 siblings, 1 reply; 4+ messages in thread From: Farhan Ali @ 2026-05-04 17:00 UTC (permalink / raw) To: Gerd Bayer, linux-s390, linux-kernel, linux-pci Cc: helgaas, lukas, alex, clg, schnelle, mjrosato, stable On 5/4/2026 8:52 AM, Gerd Bayer wrote: > On Tue, 2026-04-21 at 09:30 -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. 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(). >> > Hi Farhan, > > sorry for jumping this late into reviewing this, but I think I'd prefer > a different approach than extending the slot member to u16 to make the > full range of 256 usable: > >> 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 -1 and PCI_SLOT_ALL_DEVICES. >> >> Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") >> Cc: stable@vger.kernel.org >> Suggested-by: Niklas Schnelle <schnelle@linux.ibm.com> >> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com> >> Signed-off-by: Farhan Ali <alifm@linux.ibm.com> >> --- >> drivers/pci/hotplug/rpaphp_slot.c | 2 +- >> drivers/pci/pci.c | 5 +++-- >> drivers/pci/slot.c | 33 +++++++++++++++++++++++-------- >> include/linux/pci.h | 8 ++++++-- >> 4 files changed, 35 insertions(+), 13 deletions(-) >> >> diff --git a/drivers/pci/hotplug/rpaphp_slot.c b/drivers/pci/hotplug/rpaphp_slot.c >> index 67362e5b9971..92eabf5f61b9 100644 >> --- a/drivers/pci/hotplug/rpaphp_slot.c >> +++ b/drivers/pci/hotplug/rpaphp_slot.c >> @@ -84,7 +84,7 @@ int rpaphp_register_slot(struct slot *slot) >> struct hotplug_slot *php_slot = &slot->hotplug_slot; >> u32 my_index; >> int retval; >> - int slotno = -1; >> + int slotno = PCI_SLOT_PLACEHOLDER; >> >> dbg("%s registering slot:path[%pOF] index[%x], name[%s] pdomain[%x] type[%d]\n", >> __func__, slot->dn, slot->index, slot->name, >> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c >> index 8f7cfcc00090..d0c9f0166af5 100644 >> --- a/drivers/pci/pci.c >> +++ b/drivers/pci/pci.c >> @@ -4865,8 +4865,9 @@ 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 e0b7fb43423c..3f6e5dce27a0 100644 >> --- a/drivers/pci/slot.c >> +++ b/drivers/pci/slot.c >> @@ -37,7 +37,7 @@ static const struct sysfs_ops pci_slot_sysfs_ops = { >> >> static ssize_t address_read_file(struct pci_slot *slot, char *buf) >> { >> - if (slot->number == 0xff) >> + if (slot->number == (u16)PCI_SLOT_PLACEHOLDER) >> return sysfs_emit(buf, "%04x:%02x\n", >> pci_domain_nr(slot->bus), >> slot->bus->number); >> @@ -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); >> >> @@ -176,8 +192,7 @@ 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); >> } >> @@ -256,7 +271,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, >> >> mutex_lock(&pci_slot_mutex); >> >> - if (slot_nr == -1) >> + if (slot_nr == PCI_SLOT_PLACEHOLDER) >> goto placeholder; >> >> /* >> @@ -287,6 +302,9 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, >> 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); >> @@ -307,8 +325,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, >> >> 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 2c4454583c11..d58982aa8730 100644 >> --- a/include/linux/pci.h >> +++ b/include/linux/pci.h >> @@ -78,14 +78,18 @@ >> * 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 -1 >> >> /* 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 */ Hi Gerd, > How about you introduce two additional single-bit flag members here for > - placeholder, and > - slot_all_devices > and avoid creating an artifically wide number member. > > Eventually, this means that the special cases "placeholder-slot" and > "bus-wide slot" should be broken out of pci_create_slot(). > >> struct kobject kobj; >> }; >> > Hope this makes any sense? It almost makes me wonder if this should be > handled with a pre-cursor patch to this... I would like to avoid doing this as part of this series, and not increase it's scope too much. I do see your point about having separate flags to indicate a placeholder/slot_all_devices, but I think we would still need the special numbers unless we want to change pci_create_slot API to pass in flags. Thanks Farhan > > Thanks, > Gerd ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 2026-05-04 17:00 ` Farhan Ali @ 2026-05-06 11:55 ` Gerd Bayer 0 siblings, 0 replies; 4+ messages in thread From: Gerd Bayer @ 2026-05-06 11:55 UTC (permalink / raw) To: Farhan Ali, linux-s390, linux-kernel, linux-pci, Keith Busch Cc: helgaas, lukas, alex, clg, schnelle, mjrosato, stable On Mon, 2026-05-04 at 10:00 -0700, Farhan Ali wrote: > On 5/4/2026 8:52 AM, Gerd Bayer wrote: > > On Tue, 2026-04-21 at 09:30 -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. 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(). > > > > > Hi Farhan, > > > > sorry for jumping this late into reviewing this, but I think I'd prefer > > a different approach than extending the slot member to u16 to make the > > full range of 256 usable: > > > > > 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 -1 and PCI_SLOT_ALL_DEVICES. > > > > > > Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") > > > Cc: stable@vger.kernel.org > > > Suggested-by: Niklas Schnelle <schnelle@linux.ibm.com> > > > Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com> > > > Signed-off-by: Farhan Ali <alifm@linux.ibm.com> > > > --- > > > drivers/pci/hotplug/rpaphp_slot.c | 2 +- > > > drivers/pci/pci.c | 5 +++-- > > > drivers/pci/slot.c | 33 +++++++++++++++++++++++-------- > > > include/linux/pci.h | 8 ++++++-- > > > 4 files changed, 35 insertions(+), 13 deletions(-) > > > > > > > > > [... snip ...] > > > diff --git a/include/linux/pci.h b/include/linux/pci.h > > > index 2c4454583c11..d58982aa8730 100644 > > > --- a/include/linux/pci.h > > > +++ b/include/linux/pci.h > > > @@ -78,14 +78,18 @@ > > > * 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 -1 > > > > > > /* 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 */ > > Hi Gerd, > > > > How about you introduce two additional single-bit flag members here for > > - placeholder, and > > - slot_all_devices > > and avoid creating an artifically wide number member. > > > > Eventually, this means that the special cases "placeholder-slot" and > > "bus-wide slot" should be broken out of pci_create_slot(). > > > > > struct kobject kobj; > > > }; > > > > > Hope this makes any sense? It almost makes me wonder if this should be > > handled with a pre-cursor patch to this... > > I would like to avoid doing this as part of this series, and not > increase it's scope too much. I do see your point about having separate > flags to indicate a placeholder/slot_all_devices, but I think we would > still need the special numbers unless we want to change pci_create_slot > API to pass in flags. I think I found a way to keep that untouched with some additional changes as a pre-cursor: Below, you can find what I hacked together extending on your idea of introducing flags for the slots. That way I was able to decouple the input parameter slot_nr (int) from the actual slot->number member (u8). Caveat: I *did* change PCI_SLOT_ALL_DEVICES (similar like you) - and this is compile-tested only - and lacks all updates to comments. diff --git a/drivers/pci/hotplug/rpaphp_slot.c b/drivers/pci/hotplug/rpaphp_slot.c index 67362e5b9971..92eabf5f61b9 100644 --- a/drivers/pci/hotplug/rpaphp_slot.c +++ b/drivers/pci/hotplug/rpaphp_slot.c @@ -84,7 +84,7 @@ int rpaphp_register_slot(struct slot *slot) struct hotplug_slot *php_slot = &slot->hotplug_slot; u32 my_index; int retval; - int slotno = -1; + int slotno = PCI_SLOT_PLACEHOLDER; dbg("%s registering slot:path[%pOF] index[%x], name[%s] pdomain[%x] type[%d]\n", __func__, slot->dn, slot->index, slot->name, diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c index 6d5cd37bfb1e..b3d54197e8c9 100644 --- a/drivers/pci/slot.c +++ b/drivers/pci/slot.c @@ -37,20 +37,11 @@ static const struct sysfs_ops pci_slot_sysfs_ops = { static ssize_t address_read_file(struct pci_slot *slot, char *buf) { - if (slot->number == 0xff) + if (slot->placeholder) return sysfs_emit(buf, "%04x:%02x\n", pci_domain_nr(slot->bus), slot->bus->number); - /* - * Preserve legacy ABI expectations that hotplug drivers that manage - * multiple devices per slot emit 0 for the device number. - */ - if (slot->number == PCI_SLOT_ALL_DEVICES) - return sysfs_emit(buf, "%04x:%02x:00\n", - pci_domain_nr(slot->bus), - slot->bus->number); - return sysfs_emit(buf, "%04x:%02x:%02x\n", pci_domain_nr(slot->bus), slot->bus->number, @@ -82,7 +73,7 @@ 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 || + if (slot->bus_wide || PCI_SLOT(dev->devfn) == slot->number) dev->slot = NULL; up_read(&pci_bus_sem); @@ -187,7 +178,7 @@ 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 || + if (slot->bus_wide || PCI_SLOT(dev->devfn) == slot->number) dev->slot = slot; mutex_unlock(&pci_slot_mutex); @@ -267,7 +258,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, mutex_lock(&pci_slot_mutex); - if (slot_nr == -1) + if (slot_nr == PCI_SLOT_PLACEHOLDER) goto placeholder; /* @@ -296,7 +287,12 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, } slot->bus = pci_bus_get(parent); - slot->number = slot_nr; + if (slot_nr == PCI_SLOT_PLACEHOLDER) + slot->placeholder = 1; + else if (slot_nr == PCI_SLOT_ALL_DEVICES) + slot->bus_wide = 1; + else + slot->number = slot_nr; slot->kobj.kset = pci_slots_kset; diff --git a/include/linux/pci.h b/include/linux/pci.h index 2c4454583c11..9a27fddeb397 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -78,14 +78,17 @@ * 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 -2 +#define PCI_SLOT_PLACEHOLDER -1 /* 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 */ + unsigned char number; /* Device nr */ + unsigned int bus_wide:1; /* created with PCI_SLOT_ALL_DEVICES */ + unsigned int placeholder:1; /* special case for PPC */ struct kobject kobj; }; Nice side-effect: The special handling for bus-wide slots in address_read_file() is no longer necessary. Adding Keith Busch who introduced "bus-wide slots" just recently with 102c8b26b54e ("PCI: Allow all bus devices to use the same slot") which actually added special meanings for slot 0xfe - which is not always desired. Maybe it is time to refactor pci_create_slot() into separate variants for placeholder and bus-wide (and multifunction) slots... But that's a bigger change that is out of scope here. Thanks, Gerd ^ permalink raw reply related [flat|nested] 4+ messages in thread
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2026-04-21 16:30 ` [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 Farhan Ali
2026-05-04 15:52 ` Gerd Bayer
2026-05-04 17:00 ` Farhan Ali
2026-05-06 11:55 ` Gerd Bayer
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