Re: [PATCH v2] hw/pci: prevent hotplug of devices on pcie-root-ports on the wrong slot

[Ani Sinha]

> On 15-Jun-2023, at 4:56 PM, Igor Mammedov <imammedo@redhat.com> wrote:
> 
> On Thu, 15 Jun 2023 10:46:45 +0530
> Ani Sinha <anisinha@redhat.com> wrote:
> 
>> PCIE root ports and other upstream ports only allow one device on slot 0.
>> When hotplugging a device on a pcie root port, make sure that the device
>> address passed always represents slot 0. Any other slot 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 | 16 ++++++++++++++++
>> 1 file changed, 16 insertions(+)
>> 
>> changelog:
>> v2: feedback from mst included.
>> 
>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> index bf38905b7d..66999352cc 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),
>> @@ -1182,6 +1183,11 @@ static PCIDevice *do_pci_register_device(PCIDevice 
>> *pci_dev,
>>     } else if (dev->hotplugged &&
>>                !pci_is_vf(pci_dev) &&
>>                pci_get_function_0(pci_dev)) {
>> +        /*
>> +         * populating function 0 triggers a bus scan from the guest that
>> +         * exposes other non-zero functions. Hence we need to ensure that
>> +         * function 0 is available.
>> +         */
>>         error_setg(errp, "PCI: slot %d function 0 already occupied by %s,"
>>                    " new func %s cannot be exposed to guest.",
>>                    PCI_SLOT(pci_get_function_0(pci_dev)->devfn),
>> @@ -1189,6 +1195,16 @@ 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) && PCI_SLOT(devfn)) {
>> +        /*
>> +         * If the device is being plugged into an upstream PCIE port,
> 
> you probably mixing up downstream port with upstream one,
> the only thing that could be plugged into upstream port
> is PCIE switch.
> 
> Also I'm not sure that we should do this at all.
> Looking at BZ it seems that QEMU crashes inside backend
> and tear down/cleanup sequence is broken somewhere.
> And that is the root cause, so I'd rather fix that 1st
> and only after that consider adding workarounds if any
> were necessary.

I have added more details in the ticket. I still believe that my approach is in 
the right direction.

> 
> 
>> +         * like a pcie root port, we only support one device at slot 0
>> +         */
>> +        error_setg(errp, "PCI: slot %d is not valid for %s",
>> +                   PCI_SLOT(devfn), name);
>> +        return NULL;
>>     }
>> 
>>     pci_dev->devfn = devfn;