linux-kernel - Re: [PATCH 2/6] pci: Scan all functions when probing while running over Jailhouse

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Message-ID: <20180222205753.GE16519@bhelgaas-glaptop.roam.corp.google.com>
Date:   Thu, 22 Feb 2018 14:57:53 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jan Kiszka <jan.kiszka@...mens.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, x86@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jailhouse-dev@...glegroups.com, linux-pci@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Benedikt Spranger <b.spranger@...utronix.de>
Subject: Re: [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@...mens.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@...utronix.de>
> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>

With subject change to:

  PCI: Scan all functions when running over Jailhouse

Acked-by: Bjorn Helgaas <bhelgaas@...gle.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
>