PCI: Scan all functions when running over Jailhouse

Per PCIe r4.0, sec 7.5.1.1.9, multi-function devices are required to have a
function 0.  Therefore, Linux scans for devices at function 0 (devfn
0/8/16/...) and only scans for other functions if function 0 has its
Multi-Function Device bit set or ARI or SR-IOV indicate there are more
functions.

The Jailhouse hypervisor may pass individual functions of a multi-function
device to a guest without passing function 0, which means a Linux guest
won't find them.

Change Linux PCI probing so it scans all function numbers when running as a
guest over Jailhouse.

This is technically prohibited by the spec, so it is possible that PCI
devices without the Multi-Function Device bit set may have unexpected
behavior in response to this probe.

Originally-by: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: jailhouse-dev@googlegroups.com
Cc: Benedikt Spranger <b.spranger@linutronix.de>
Cc: linux-pci@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Link: https://lkml.kernel.org/r/06e279b2a3e06cf6689ab3975f8ab592bba02362.1520408357.git.jan.kiszka@siemens.com

drivers/pci/probe.c

@@ -16,6 +16,7 @@
 #include <linux/pci-aspm.h>
 #include <linux/aer.h>
 #include <linux/acpi.h>
+#include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
 #include "pci.h"
@@ -2518,14 +2519,29 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
 {
 	unsigned int used_buses, normal_bridges = 0, hotplug_bridges = 0;
 	unsigned int start = bus->busn_res.start;
-	unsigned int devfn, cmax, max = start;
+	unsigned int devfn, fn, cmax, max = start;
 	struct pci_dev *dev;
+	int nr_devs;
 
 	dev_dbg(&bus->dev, "scanning bus\n");
 
 	/* Go find them, Rover! */
-	for (devfn = 0; devfn < 0x100; devfn += 8)
-		pci_scan_slot(bus, devfn);
+	for (devfn = 0; devfn < 256; devfn += 8) {
+		nr_devs = pci_scan_slot(bus, devfn);
+
+		/*
+		 * The Jailhouse hypervisor may pass individual functions of a
+		 * multi-function device to a guest without passing function 0.
+		 * Look for them as well.
+		 */
+		if (jailhouse_paravirt() && nr_devs == 0) {
+			for (fn = 1; fn < 8; fn++) {
+				dev = pci_scan_single_device(bus, devfn + fn);
+				if (dev)
+					dev->multifunction = 1;
+			}
+		}
+	}
 
 	/* Reserve buses for SR-IOV capability */
 	used_buses = pci_iov_bus_range(bus);