Re: [PATCH] hw/pci: prevent hotplug of devices on pcie-root-ports with wrong devfn address

[Ani Sinha]

> On 14-Jun-2023, at 6:31 PM, Igor Mammedov <imammedo@redhat.com> wrote:
> 
> On Wed, 14 Jun 2023 18:01:50 +0530
> Ani Sinha <anisinha@redhat.com> wrote:
> 
>> PCIE root ports only allow one device on slot 0/function 0. When hotplugging 
>> a
>> device on a pcie root port, make sure that the device address passed is
>> always 0x00 that represents slot 0 and function 0. Any other slot value and
>> function value would be illegal on a root port.
>> 
>> CC: jusual@redhat.com
>> CC: imammedo@redhat.com
>> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2128929
>> Signed-off-by: Ani Sinha <anisinha@redhat.com>
>> ---
>> hw/pci/pci.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>> 
>> Note:
>> I tested this with both native and acpi hotplug enabled on pcie. The
>> check seems to work on both.
>> 
>> (qemu)  netdev_add socket,id=hostnet1,listen=:1234
>> (qemu) device_add 
>> e1000e,netdev=hostnet1,mac=00:11:22:33:44:03,id=net1,bus=pci.6,addr=0x2.0x5
>> Error: PCI: slot 2 function 5 is not valid for e1000e
>> (qemu) device_add 
>> e1000e,netdev=hostnet1,mac=00:11:22:33:44:03,id=net1,bus=pci.6,addr=0x0.0
>> (qemu) info network
>> net1: index=0,type=nic,model=e1000e,macaddr=00:11:22:33:44:03
>> \ hostnet1: index=0,type=socket,
>> (qemu) device_del net1
>> (qemu) info network
>> hostnet1: index=0,type=socket,
>> 
>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> index bf38905b7d..bc39322dfd 100644
>> --- a/hw/pci/pci.c
>> +++ b/hw/pci/pci.c
>> @@ -64,6 +64,7 @@ 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),
>> @@ -1189,6 +1190,14 @@ static PCIDevice *do_pci_register_device(PCIDevice 
>> *pci_dev,
>>                    name);
>> 
>>        return NULL;
>> +    } else if (dev->hotplugged &&
> 
>> +               !pci_is_vf(pci_dev) &&
>> +               pcie_has_upstream_port(pci_dev) 
> can you clarify what above 2 lines are here for?
> 
> you can't hotplug anything into upstream port (only downstream)

This code checks if the hot plugged device is being plugged into a pcie root 
port. For pcie root ports, only slot 0 can be used. Please see 
3f1e1478db2d67098d9 . The conditional check just above this hunk therefore 
checks for unoccupied function 0 in slot 0 if the device is plugged into an 
upstream pcie root port. I think for hot plugs, only function 0 is allowed.

As for vf, I am not sure. I believe for vfs the restriction is not valid. I 
just kept the check based on the conditional just prior to it.

> and why _vf() is here also not clear.
> 
>> && devfn) {
>> +        /* For an upstream PCIE port, we only support one device at slot 0 
>> */
>> +        error_setg(errp, "PCI: slot %d function %d is not valid for %s",
>> +                   PCI_SLOT(devfn), PCI_FUNC(devfn), name);
>> +        return NULL;
>> +
>>     }
>> 
>>     pci_dev->devfn = devfn;