Re: [PATCH v7 5/6] hw/pci: ensure PCIE devices are plugged into only slot 0 of PCIE port

[Ani Sinha]

> On 04-Jul-2023, at 5:24 PM, Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
> 
> On 2023/07/04 20:25, Ani Sinha wrote:
>> PCI Express ports only have one slot, so PCI Express devices can only be
>> plugged into slot 0 on a PCIE port. Add a warning to let users know when the
>> invalid configuration is used. We may enforce this more strongly later on 
>> once
>> we get more clarity on whether we are introducing a bad regression for users
>> currenly using the wrong configuration.
>> The change has been tested to not break or alter behaviors of ARI capable
>> devices by instantiating seven vfs on an emulated igb device (the maximum
>> number of vfs the linux igb driver supports). The vfs instantiated correctly
>> and are seen to have non-zero device/slot numbers in the conventional PCI BDF
>> representation.
>> CC: jusual@redhat.com
>> CC: imammedo@redhat.com
>> CC: mst@redhat.com
>> CC: akihiko.odaki@daynix.com
>> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2128929
>> Signed-off-by: Ani Sinha <anisinha@redhat.com>
>> Reviewed-by: Julia Suvorova <jusual@redhat.com>
>> ---
>>  hw/pci/pci.c | 15 +++++++++++++++
>>  1 file changed, 15 insertions(+)
>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> index e2eb4c3b4a..47517ba3db 100644
>> --- a/hw/pci/pci.c
>> +++ b/hw/pci/pci.c
>> @@ -65,6 +65,7 @@ bool pci_available = true;
>>  static char *pcibus_get_dev_path(DeviceState *dev);
>>  static char *pcibus_get_fw_dev_path(DeviceState *dev);
>>  static void pcibus_reset(BusState *qbus);
>> +static bool pcie_has_upstream_port(PCIDevice *dev);
>>    static Property pci_props[] = {
>>      DEFINE_PROP_PCI_DEVFN("addr", PCIDevice, devfn, -1),
>> @@ -2121,6 +2122,20 @@ static void pci_qdev_realize(DeviceState *qdev, Error 
>> **errp)
>>          }
>>      }
>>  +    /*
>> +     * With SRIOV and ARI, vfs can have non-zero slot in the conventional
>> +     * PCI interpretation as all five bits reserved for slot addresses are
>> +     * also used for function bits for the various vfs. Ignore that case.
> 
> You don't have to mention SR/IOV; it affects all ARI-capable devices. A PF 
> can also have non-zero slot number in the conventional interpretation so you 
> shouldn't call it vf either.

Can you please help write a comment that explains this properly for all cases - 
ARI/non-ARI, PFs and VFs? Once everyone agrees that its clear and correct, I 
will re-spin.

> 
>> +     */
>> +    if (pci_is_express(pci_dev) &&
>> +        !pcie_find_capability(pci_dev, PCI_EXT_CAP_ID_ARI) &&
>> +        pcie_has_upstream_port(pci_dev) &&
>> +        PCI_SLOT(pci_dev->devfn)) {
>> +        warn_report("PCI: slot %d is not valid for %s,"
>> +                    " parent device only allows plugging into slot 0.",
>> +                    PCI_SLOT(pci_dev->devfn), pci_dev->name);
>> +    }
>> +
>>      if (pci_dev->failover_pair_id) {
>>          if (!pci_bus_is_express(pci_get_bus(pci_dev))) {
>>              error_setg(errp, "failover primary device must be on "
>