* [PATCH v15 1/7] PCI: Allow per function PCI slots to fix slot reset on s390
[not found] <20260505200510.2954-1-alifm@linux.ibm.com>
@ 2026-05-05 20:05 ` Farhan Ali
0 siblings, 0 replies; only message in thread
From: Farhan Ali @ 2026-05-05 20:05 UTC (permalink / raw)
To: linux-s390, linux-kernel, linux-pci
Cc: helgaas, alex, 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 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)
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);
}
@@ -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)
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 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
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