[K][PATCH 4/5] PCI: Extend isolated function probing to s390

[frank.heimes at canonical.com]

From: Niklas Schnelle <schnelle at linux.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1959542

Like the jailhouse hypervisor, s390's PCI architecture allows passing
isolated PCI functions to a guest OS instance. As of now this is was not
utilized even with multi-function support as the s390 PCI code makes sure
that only virtual PCI busses including a function with devfn 0 are
presented to the PCI subsystem. A subsequent change will remove this
restriction.

Allow probing such functions by replacing the existing check for
jailhouse_paravirt() with a new hypervisor_isolated_pci_functions() helper.

Link: https://lore.kernel.org/r/20220628143100.3228092-5-schnelle@linux.ibm.com
Signed-off-by: Niklas Schnelle <schnelle at linux.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
Reviewed-by: Pierre Morel <pmorel at linux.ibm.com>
Cc: Jan Kiszka <jan.kiszka at siemens.com>
(cherry picked from commit 189c6c33ff421def040b904fb14ef76c5bf5af4c)
Signed-off-by: Frank Heimes <frank.heimes at canonical.com>
---
 drivers/pci/probe.c        | 2 +-
 include/linux/hypervisor.h | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 1f91ed67b5c5..4948531481d1 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2668,7 +2668,7 @@ int pci_scan_slot(struct pci_bus *bus, int devfn)
 			 * a hypervisor that passes through individual PCI
 			 * functions.
 			 */
-			if (!jailhouse_paravirt())
+			if (!hypervisor_isolated_pci_functions())
 				break;
 		}
 		fn = next_fn(bus, dev, fn);
diff --git a/include/linux/hypervisor.h b/include/linux/hypervisor.h
index fc08b433c856..9efbc54e35e5 100644
--- a/include/linux/hypervisor.h
+++ b/include/linux/hypervisor.h
@@ -32,4 +32,12 @@ static inline bool jailhouse_paravirt(void)
 
 #endif /* !CONFIG_X86 */
 
+static inline bool hypervisor_isolated_pci_functions(void)
+{
+	if (IS_ENABLED(CONFIG_S390))
+		return true;
+
+	return jailhouse_paravirt();
+}
+
 #endif /* __LINUX_HYPEVISOR_H */
-- 
2.25.1