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Mon, 4 May 2026 15:52:37 +0000 (GMT) Message-ID: Subject: Re: [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 From: Gerd Bayer To: Farhan Ali , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Cc: helgaas@kernel.org, lukas@wunner.de, alex@shazbot.org, clg@redhat.com, schnelle@linux.ibm.com, mjrosato@linux.ibm.com, stable@vger.kernel.org Date: Mon, 04 May 2026 17:52:36 +0200 In-Reply-To: <20260421163031.704-2-alifm@linux.ibm.com> References: <20260421163031.704-1-alifm@linux.ibm.com> <20260421163031.704-2-alifm@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 (3.58.3-1.fc43) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA0MDE1NCBTYWx0ZWRfX9/Ql5X7w1FjA iQDPLKBeVq3ZHopJh0UQOLsgMrQtIhyQfRilRvStftz6OOgKhq+HfcHg6TQ16BDEioj29qwWaUs jCNpLVycSeASVj3peJJ7FAPpcB96uRu2edgCHrHds9ruYB3gbZVbvr6YJdJj7S8GaON805K6naK vjPfIdUefsNTux6M656eAmRkoBXo91CnkVj+H/Em8nGzCsi4pqUUbAxaPJ/JDcPoLMY+2zoMLpl P2B/V55tCoYJgckufJPBJ8WEfUNCXh+mlcwwnYbu71dWrzgpj7ccplcMcXkGGP3+/0FzqsBlMJ7 pvWC2kdubf/o1OOu+adbh7PhK+BLa25sbN+8H6RIyDUzHATs+2v4yr43qsIZEjbLFlMD7FkpF0V 324Wr80OFJr1kQ+liH3YfzipBwwiQWAr8wC1/OtMSNa2EJj06yO+9Od+dmKgM1mEvbKfJRfssC6 1Uigf0Ue3tYsl/qyMwQ== X-Proofpoint-ORIG-GUID: RUHU29tJsx3lGCDMbdRrrIZSFqxbHcB2 X-Proofpoint-GUID: RUHU29tJsx3lGCDMbdRrrIZSFqxbHcB2 X-Authority-Analysis: v=2.4 cv=W7UIkxWk c=1 sm=1 tr=0 ts=69f8c0ca cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=bDQvo4m8Rz4M5vCSQ40A:9 a=QEXdDO2ut3YA:10 a=O8hF6Hzn-FEA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-04_05,2026-04-30_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 adultscore=0 lowpriorityscore=0 malwarescore=0 suspectscore=0 spamscore=0 clxscore=1011 phishscore=0 bulkscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605040154 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. >=20 > 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 resetti= ng > a function through the hotplug driver's slot_reset() interface. >=20 > When attempting to reset a function through the hotplug driver, the share= d > 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(). >=20 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. >=20 > Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions") > Cc: stable@vger.kernel.org > Suggested-by: Niklas Schnelle > Reviewed-by: Niklas Schnelle > Signed-off-by: Farhan Ali > --- > 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(-) >=20 > diff --git a/drivers/pci/hotplug/rpaphp_slot.c b/drivers/pci/hotplug/rpap= hp_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 =3D &slot->hotplug_slot; > u32 my_index; > int retval; > - int slotno =3D -1; > + int slotno =3D PCI_SLOT_PLACEHOLDER; > =20 > dbg("%s registering slot:path[%pOF] index[%x], name[%s] pdomain[%x] typ= e[%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_sl= ot *hotplug, bool probe) > =20 > 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; > =20 > 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 =3D { > =20 > static ssize_t address_read_file(struct pci_slot *slot, char *buf) > { > - if (slot->number =3D=3D 0xff) > + if (slot->number =3D=3D (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 *sl= ot, char *buf) > return bus_speed_read(slot->bus->cur_bus_speed, buf); > } > =20 > +static bool pci_dev_matches_slot(struct pci_dev *dev, struct pci_slot *s= lot) > +{ > + if (slot->per_func_slot) > + return dev->devfn =3D=3D slot->number; > + > + return slot->number =3D=3D PCI_SLOT_ALL_DEVICES || > + PCI_SLOT(dev->devfn) =3D=3D 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) > =20 > down_read(&pci_bus_sem); > list_for_each_entry(dev, &slot->bus->devices, bus_list) > - if (slot->number =3D=3D PCI_SLOT_ALL_DEVICES || > - PCI_SLOT(dev->devfn) =3D=3D slot->number) > + if (pci_dev_matches_slot(dev, slot)) > dev->slot =3D NULL; > up_read(&pci_bus_sem); > =20 > @@ -176,8 +192,7 @@ void pci_dev_assign_slot(struct pci_dev *dev) > =20 > mutex_lock(&pci_slot_mutex); > list_for_each_entry(slot, &dev->bus->slots, list) > - if (slot->number =3D=3D PCI_SLOT_ALL_DEVICES || > - PCI_SLOT(dev->devfn) =3D=3D slot->number) > + if (pci_dev_matches_slot(dev, slot)) > dev->slot =3D slot; > mutex_unlock(&pci_slot_mutex); > } > @@ -256,7 +271,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *pare= nt, int slot_nr, > =20 > mutex_lock(&pci_slot_mutex); > =20 > - if (slot_nr =3D=3D -1) > + if (slot_nr =3D=3D PCI_SLOT_PLACEHOLDER) > goto placeholder; > =20 > /* > @@ -287,6 +302,9 @@ struct pci_slot *pci_create_slot(struct pci_bus *pare= nt, int slot_nr, > slot->bus =3D pci_bus_get(parent); > slot->number =3D slot_nr; > =20 > + if (pci_slot_enabled_per_func()) > + slot->per_func_slot =3D 1; > + > slot->kobj.kset =3D pci_slots_kset; > =20 > slot_name =3D make_slot_name(name); > @@ -307,8 +325,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *pare= nt, int slot_nr, > =20 > down_read(&pci_bus_sem); > list_for_each_entry(dev, &parent->devices, bus_list) > - if (slot_nr =3D=3D PCI_SLOT_ALL_DEVICES || > - PCI_SLOT(dev->devfn) =3D=3D slot_nr) > + if (pci_dev_matches_slot(dev, slot)) > dev->slot =3D slot; > up_read(&pci_bus_sem); > =20 > 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 mult= iple > * 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 > =20 > /* 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; > }; >=20 Hope this makes any sense? It almost makes me wonder if this should be handled with a pre-cursor patch to this... Thanks, Gerd