Re: [PATCH v6 3/5] PCI: Move jailhouse's isolated function handling to pci_scan_slot()

Pierre Morel
2022-06-30T12:43:05Z

On 6/28/22 16:30, Niklas Schnelle wrote:
> The special case of the jailhouse hypervisor passing through individual
> PCI functions handles scanning for PCI functions even if function 0 does
> not exist. Currently this is done with an extra loop duplicating the one
> in pci_scan_slot(). By incorporating the check for jailhouse_paravirt()
> into pci_scan_slot() we can instead do this as part of the normal
> slot scan. Note that with the assignment of dev->multifunction gated by
> fn > 0 we set dev->multifunction unconditionally for all functions if
> function 0 is missing just as in the existing jailhouse loop.
>
> The only functional change is that we now call
> pcie_aspm_init_link_state() for these functions but this already
> happened if function 0 was passed through and should not be a problem.
>
> Cc: Jan Kiszka <jan.kiszka@siemens.com>
> Link: https://lore.kernel.org/linux-pci/20220408224514.GA353445@bhelgaas/
> Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
> drivers/pci/probe.c | 30 ++++++++++--------------------
> 1 file changed, 10 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 2c737dce757e..a18e07e6a7df 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2662,8 +2662,13 @@ int pci_scan_slot(struct pci_bus *bus, int devfn)
> if (fn > 0)
> dev->multifunction = 1;
> } else if (fn == 0) {
> - /* function 0 is required */
> - break;
> + /*
> + * function 0 is required unless we are running on
> + * a hypervisor which passes through individual PCI
> + * functions.
> + */
> + if (!jailhouse_paravirt())
> + break;
> }
> fn = next_fn(bus, dev, fn);
> } while (fn >= 0);
> @@ -2862,29 +2867,14 @@ 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, fn, cmax, max = start;
> + unsigned int devfn, 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 < 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;
> - }
> - }
> - }
> + for (devfn = 0; devfn < 256; devfn += 8)
> + pci_scan_slot(bus, devfn);
>
> /* Reserve buses for SR-IOV capability */
> used_buses = pci_iov_bus_range(bus);
>

Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>

--
Pierre Morel
IBM Lab Boeblingen