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Fri, 31 Jul 2026 18:15:17 +0000 (GMT) Received: from [9.61.254.127] (unknown [9.61.254.127]) by smtpav02.wdc07v.mail.ibm.com (Postfix) with ESMTP; Fri, 31 Jul 2026 18:15:17 +0000 (GMT) Message-ID: <08ce08f7-66fd-430a-8eea-6b1696f68de6@linux.ibm.com> Date: Fri, 31 Jul 2026 11:15:16 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v22 1/4] PCI: Allow per function PCI slots to fix slot reset on s390 To: Bjorn Helgaas Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, alex@shazbot.org, schnelle@linux.ibm.com, mjrosato@linux.ibm.com, stable@vger.kernel.org, Keith Busch References: <20260731002210.GA1521769@bhelgaas> Content-Language: en-US From: Farhan Ali In-Reply-To: <20260731002210.GA1521769@bhelgaas> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: SbFnyJyiiEWBeQZ9o3X-H2TMZslrFWUr X-Proofpoint-Spam-Info: AW1haW4tMjYwNzMxMDEzNiBTYWx0ZWRfX8t021t0VWdvO wZOvhEe8iwBTeqbcKQMzGVoUvagzWSIocPCTKI0NmD1e+36t8X+AIfqQpuEFx+8TTeyKkQI8Hp6 kk1r+u2gIToxTidSSe2XdGU7Rc6IAbI= X-Authority-Analysis: v=2.4 cv=E/z9Y6dl c=1 sm=1 tr=0 ts=6a6ce638 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=TxOPuv4DIxgBshNE3IgA:9 a=QEXdDO2ut3YA:10 a=O8hF6Hzn-FEA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzMxMDEzNiBTYWx0ZWRfXxIY5Jq+iWrah bBrim3MrGwgVYtyGC1TitsvycrB5R1Ea+lyfNfTxhOiGJXuN3kT8/53FSoL9Fks0+8doorYrug7 zR/JnqN2r21XJ18WwVMZWpA6wvP0ay6/4pATGJOMCS2f9+/PV9sFAyTsYlZBnqSsybAw5u0/VKU mRwHgdPZdAB20WVPxchZinmDPjDpUrnXgWy6jJ9ReHGQl13vKqqNkT02B+VuI8/o9HLufoROZdb UIbMqWp1xqNxOXgVpmQ/TcyNoeFKjObN0+6vbY2gjG/QEjIgkEAjmeb/yhdEXUFinAwEtISFs6H 04CW5zy6i5k9divf5flPIQiS6hlUIZppKd+/Do7+SQgtgDAMMno6C5DlWLMJ3B+0LvAUmfAryNv OV26dlOLOuJLQKs82x0yvs3fykMC5HLlG0TUczU+ZUZHZbkjgjZz68SWxheb/ovkMTl19DhWNLK nIizbUyRUEQS4V6nYMg== X-Proofpoint-GUID: SbFnyJyiiEWBeQZ9o3X-H2TMZslrFWUr X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-31_05,2026-07-30_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 spamscore=0 clxscore=1015 phishscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607310136 On 7/30/2026 5:22 PM, Bjorn Helgaas wrote: > [+cc Keith, just fyi since this is slightly related to 102c8b26b54e > ("PCI: Allow all bus devices to use the same slot")] > > On Mon, Jul 20, 2026 at 12:25:02PM -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. > I guess we must be talking about rpaphp? No, this is the s390_pci_hpc driver. >> Currently, the pci_create_slot() assigns the same pci_slot object to >> multifunction devices. > Can we say something about exactly where and why this reuse happens? > Is this because most callers have stripped off the function number by > using PCI_SLOT() before they pass it to pci_create_slot() as @slot_nr? > > If so, it seems like more a property of the *callers*, not of > pci_create_slot() itself. AFAIU in pci_create_slot() we will iterate through all the devices in the bus, and assign the same pci_slot object to devices that falls in the same slot as per PCI_SLOT(). So even if a caller provides different slot_nr, devices that fall in the same slot will be assigned the same object. In s390 hotplug driver case, it provides the devfn as the slot_nr. So for example devices with bdf 00:00.0 and bdf 00:00.2 will get assigned the same slot, when we create a slot for device 00:00.0. When we attempt to create a slot for device 00:00.2, we do indeed create a separate slot object, but don't update the device's pci_slot as PCI_SLOT(00:00.2) != 2. I am open to suggestion on how we should re-word this. But i think it's pci_create_slot() that strips the devfn to a slot number. > >> 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. > Sorry for the delay in reviewing this. I always struggle to find > my way through the PCI slot code, which has grown into a bit of a > maze. I keep hoping we can simplify it somehow. I don't think that > time is now, but the complexity does make changes messy. Thank you for reviewing this! I appreciate you taking the time to help with the review. > >> 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(-) >> >> 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 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 6d5cd37bfb1e..894d6213ed30 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) > I think it might be worth splitting the PCI_SLOT_PLACEHOLDER addition > and the relevant kernel-doc updates, which are mostly unrelated to > this patch, to a separate no-functional-changes patch to simplify this > patch. I will take a look at splitting the PCI_SLOT_PLACEHOLDER out of this patch. >> 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); >> >> @@ -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); >> } > Update pci_create_slot() kernel-doc to mention PCI_SLOT_PLACEHOLDER > instead of "-1" (several instances). > > In addition to PCI_SLOT_PLACEHOLDER or PCI_SLOT_ALL_DEVICES, and a > 0-31 PCI_SLOT(devfn) value, I think @slot_nr can already be a 0-255 > value (e.g., from cpci module parameters or s390 > zpci_bus_add_device()). > > It seems like this patch also needs pci_slot.number to end up with a > complete devfn in it so pci_dev_matches_slot() can use it, but I'm > confused about how that happens, since it looks like > rpaphp_register_slot() will pass either PCI_SLOT_PLACEHOLDER or a > PCI_SLOT(...) value to pci_hp_register(). On s390 it happens via zpci_init_slot() in the drivers/pci/hotplug/s390_pci_hpc.c, which assigns a devfn as a slot_nr. > >> @@ -267,7 +282,7 @@ 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) > No action for you here, but one thing that complicates this is the > overloading of slot_nr for different purposes: > > - Sentinel flags: > > * PCI_SLOT_ALL_DEVICES (0xfe or 0xfeff) used by pciehp init_slot() > > * PCI_SLOT_PLACEHOLDER (-1), used by rpaphp_register_slot() > > * -1 may also be used by pnv_php_alloc_slot(); I don't know > exactly what it means > > - Traditional (mostly) PCI device numbers: > > * 0-31 derived by PCI_SLOT() in hv_pci_assign_slots(), > octep_hp_register_slot(), pnv_php_alloc_slot(), > rpaphp_register_slot() > > * 0-255 from cpci (module parameters) > > * 0-15 from cpq ((u8 from readb(SLOT_MASK) >> 4)) > > * 0 from ibmphp_ebda > > * 0-255 from s390 zpci_bus_add_device() > (zdev->rid & ZPCI_RID_MASK_DEVFN), where ZPCI_RID_MASK_DEVFN is > 0xff > > * 0-255 for s390 per-function slots (this series) > > - Arbitrary values: > > * Sparc pcie_bus_slot_names() path uses unvalidated > 'physical-slot#' DT property as slot_nr > > * acpiphp uses the value of _ADR as slot_nr (per spec it should be > device number in bits 16-31, but not validated) > >> goto placeholder; >> >> /* >> @@ -298,6 +313,9 @@ 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); >> @@ -318,8 +336,7 @@ 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 64b308b6e61c..6141787f7417 100644 >> --- a/include/linux/pci.h >> +++ b/include/linux/pci.h >> @@ -79,14 +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 -1 > Since this is eventually assigned to a u16, and you use "0xfeff" for > PCI_SLOT_ALL_DEVICES, it seems like "0xffff" would be appropriate. > > I suppose you used -1 because the arguments to pci_hp_register() all > the way down to pci_create_slot() are "int" and it's only inside > pci_create_slot() where it gets chopped to u16 when it's stored in > pci_slot.number. But the mix of int/u16 and 0xfeff (a valid u16) and > -1 (which needs to be int) seems like unnecessary complexity. I kept it as -1 because it's an int up until pci_create_slot(). I can change it to 0xffff. Thanks Farhan > > AFAICT the only values we need to *store* in pci_slot are 0-255 and > the "ALL_DEVICES" indication. > >> /* 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 >>