linux-kernel - [PATCH v2 3/9] PCI: Allow per function PCI slots for hypervisor isolated functions

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Message-ID: <20250825171226.1602-4-alifm@linux.ibm.com>
Date: Mon, 25 Aug 2025 10:12:20 -0700
From: Farhan Ali <alifm@...ux.ibm.com>
To: linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc: alex.williamson@...hat.com, helgaas@...nel.org, alifm@...ux.ibm.com,
        schnelle@...ux.ibm.com, mjrosato@...ux.ibm.com
Subject: [PATCH v2 3/9] PCI: Allow per function PCI slots for hypervisor isolated functions

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. 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().

This patch adds a helper function to allow per function PCI slots for
functions managed through a hypervisor which exposes individual PCI
functions while retaining the topology.

Fixes: 44510d6fa0c0 ("s390/pci: Handling multifunctions")
Co-developed-by: Niklas Schnelle <schnelle@...ux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
Signed-off-by: Farhan Ali <alifm@...ux.ibm.com>
---
 drivers/pci/slot.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
index 50fb3eb595fe..991526af0ffe 100644
--- a/drivers/pci/slot.c
+++ b/drivers/pci/slot.c
@@ -5,6 +5,7 @@
  *	Alex Chiang <achiang@...com>
  */

+#include <linux/hypervisor.h>
 #include <linux/kobject.h>
 #include <linux/slab.h>
 #include <linux/pci.h>
@@ -73,7 +74,7 @@ static void pci_slot_release(struct kobject *kobj)

 	down_read(&pci_bus_sem);
 	list_for_each_entry(dev, &slot->bus->devices, bus_list)
-		if (PCI_SLOT(dev->devfn) == slot->number)
+		if (dev->slot == slot->number)
 			dev->slot = NULL;
 	up_read(&pci_bus_sem);

@@ -160,13 +161,25 @@ static int rename_slot(struct pci_slot *slot, const char *name)
 	return result;
 }

+static bool pci_dev_matches_slot(struct pci_dev *dev, struct pci_slot *slot)
+{
+	if (hypervisor_isolated_pci_functions()) {
+		if (dev->devfn == slot->number)
+			return true;
+	} else {
+		if (PCI_SLOT(dev->devfn) == slot->number)
+			return true;
+	}
+	return false;
+}
+
 void pci_dev_assign_slot(struct pci_dev *dev)
 {
 	struct pci_slot *slot;

 	mutex_lock(&pci_slot_mutex);
 	list_for_each_entry(slot, &dev->bus->slots, list)
-		if (PCI_SLOT(dev->devfn) == slot->number)
+		if (pci_dev_matches_slot(dev, slot))
 			dev->slot = slot;
 	mutex_unlock(&pci_slot_mutex);
 }
@@ -285,7 +298,7 @@ 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 (PCI_SLOT(dev->devfn) == slot_nr)
+		if (pci_dev_matches_slot(dev, slot))
 			dev->slot = slot;
 	up_read(&pci_bus_sem);

-- 
2.43.0