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Mon, 4 May 2026 17:00:37 +0000 (GMT) Message-ID: <536665e8-47fa-48d7-b22b-1d7133001f74@linux.ibm.com> Date: Mon, 4 May 2026 10:00:36 -0700 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v14 1/7] PCI: Allow per function PCI slots to fix slot reset on s390 To: Gerd Bayer , 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 References: <20260421163031.704-1-alifm@linux.ibm.com> <20260421163031.704-2-alifm@linux.ibm.com> Content-Language: en-US From: Farhan Ali In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: yAQLfe-BNZp_qQIabfh9_bNVLJgAxnsg X-Proofpoint-GUID: yAQLfe-BNZp_qQIabfh9_bNVLJgAxnsg X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA0MDE1NCBTYWx0ZWRfX85tOrVNWsZzk pDCdUx57yGVfGEoCX27sOwD4gYfj0ht1Z8N2frmXeXzuYlPYRwBGnX58MNfRx/GFCnxF6tVjXyX zrcUQ1EAXuw8zkalBAyvZR8CYQ+XOpaP+huSRPhfBd8QBmOyz5iG9fMs/grllRGSllwqt/AXLoa b4DwrNanmBC9nJOc9RKPS5M6sIYGR5/sWDLzDsffJbezRnyrNW5XbnOUzh8vuLkKC+tcv0fjEik 6ESEVgKHi+4+vo3Rbx9ix5dHCzsuB/bG2KoTrUAHZSHv4FS6Ql7d+ReEFF8xS5n8ZwpMeBEGwq5 YWmfmTLYLQ76C99yRgou+fxPgLMUQYqVWujXVNJCDtGyNXewf/ysZxdmJiNyflLQ8nuQsNQfo23 8hIL/fZUbsorbMkfoWwbAFmckSr6IPQg4fbb/GYYtrhe6nflxtlnATYLAt2ecPVNcfqHiKbDTpH h/Mu8+MGpd63jmrK0iA== X-Authority-Analysis: v=2.4 cv=UbFhjqSN c=1 sm=1 tr=0 ts=69f8d0b7 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=7oLPNsgWg75vrdFgU7cA: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 clxscore=1015 spamscore=0 lowpriorityscore=0 malwarescore=0 suspectscore=0 adultscore=0 priorityscore=1501 bulkscore=0 phishscore=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 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 >> 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 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