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SubjectRe: [PATCH 2/6] pci: Scan all functions when probing while running over Jailhouse
On Mon, Jan 22, 2018 at 07:12:46AM +0100, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
>
> PCI and PCIBIOS probing only scans devices at function number 0/8/16/...
> Subdevices (e.g. multiqueue) have function numbers which are not a
> multiple of 8.

Suggested text:

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.

> The simple hypervisor Jailhouse passes subdevices directly w/o providing
> a virtual PCI topology like KVM. As a consequence a PCI passthrough from
> Jailhouse to a guest will not be detected by Linux.
>
> 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@linutronix.de>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

With subject change to:

PCI: Scan all functions when running over Jailhouse

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
> 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..a7b0476b4f44 100644
> --- a/arch/x86/pci/legacy.c
> +++ b/arch/x86/pci/legacy.c
> @@ -5,6 +5,7 @@
> #include <linux/export.h>
> #include <linux/pci.h>
> #include <asm/pci_x86.h>
> +#include <asm/jailhouse_para.h>
>
> /*
> * Discover remaining PCI buses in case there are peer host bridges.
> @@ -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 14e0ea1ff38b..60ad14c8245f 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -17,6 +17,7 @@
> #include <linux/acpi.h>
> #include <linux/irqdomain.h>
> #include <linux/pm_runtime.h>
> +#include <linux/hypervisor.h>
> #include "pci.h"
>
> #define CARDBUS_LATENCY_TIMER 176 /* secondary latency timer */
> @@ -2454,6 +2455,7 @@ 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;
> @@ -2461,7 +2463,7 @@ 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
>

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