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Subject[PATCH v4 2/7] PCI: Scan all functions when running over Jailhouse
Date
From: Jan Kiszka <jan.kiszka@siemens.com>

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.

Derived from original patch by Benedikt Spranger.

CC: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
---
arch/x86/pci/legacy.c | 4 +++-
drivers/pci/probe.c | 22 +++++++++++++++++++---
2 files changed, 22 insertions(+), 4 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..3c365dc996e7 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"
@@ -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);
--
2.13.6
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