[PATCH v2 2/6] PCI: Scan all functions when running over Jailhouse

[Jan Kiszka]

From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>

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.

Based on patch by Benedikt Spranger, adding Jailhouse probing to avoid
changing the behavior in the absence of the hypervisor.

CC: Benedikt Spranger <b.spranger@xxxxxxxxxxxxx>
Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
---
 arch/x86/pci/legacy.c | 4 +++-
 drivers/pci/probe.c   | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/pci/legacy.c b/arch/x86/pci/legacy.c
index 1cb01abcb1be..dfbe6ac38830 100644
--- a/arch/x86/pci/legacy.c
+++ b/arch/x86/pci/legacy.c
@@ -4,6 +4,7 @@
 #include <linux/init.h>
 #include <linux/export.h>
 #include <linux/pci.h>
+#include <asm/jailhouse_para.h>
 #include <asm/pci_x86.h>
 
 /*
@@ -34,13 +35,14 @@ int __init pci_legacy_init(void)
 
 void pcibios_scan_specific_bus(int busn)
 {
+	int stride = jailhouse_paravirt() ? 1 : 8;
 	int devfn;
 	u32 l;
 
 	if (pci_find_bus(0, busn))
 		return;
 
-	for (devfn = 0; devfn < 256; devfn += 8) {
+	for (devfn = 0; devfn < 256; devfn += stride) {
 		if (!raw_pci_read(0, busn, devfn, PCI_VENDOR_ID, 2, &l) &&
 		    l != 0x0000 && l != 0xffff) {
 			DBG("Found device at %02x:%02x [%04x]\n", busn, devfn, l);
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index ef5377438a1e..ce728251ae36 100644
--- a/drivers/pci/probe.c
+++ b/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"
@@ -2517,6 +2518,7 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
 					      unsigned int available_buses)
 {
 	unsigned int used_buses, normal_bridges = 0, hotplug_bridges = 0;
+	unsigned int stride = jailhouse_paravirt() ? 1 : 8;
 	unsigned int start = bus->busn_res.start;
 	unsigned int devfn, cmax, max = start;
 	struct pci_dev *dev;
@@ -2524,7 +2526,7 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
 	dev_dbg(&bus->dev, "scanning bus\n");
 
 	/* Go find them, Rover! */
-	for (devfn = 0; devfn < 0x100; devfn += 8)
+	for (devfn = 0; devfn < 0x100; devfn += stride)
 		pci_scan_slot(bus, devfn);
 
 	/* Reserve buses for SR-IOV capability */
-- 
2.13.6