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

[Akihiko Odaki <akihiko.odaki@daynix.com>]

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.

> +     */
> +    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 "