Re: [PATCH v16 03/13] hw/ppc/spapr_pci: Do not reject VFs created after a PF

[Shivaprasad G Bhat <sbhat@linux.ibm.com>]

On 9/18/24 7:57 PM, Cédric Le Goater wrote:
> Adding :
>
>   Harsh for QEMU/PPC pseries machine,
>   Shivaprasad for KVM/PPC VFIO and IOMMU support.
>
> Thanks,
>
> C.
>
>
> On 9/13/24 05:44, Akihiko Odaki wrote:
>> A PF may automatically create VFs and the PF may be function 0.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>> ---
>>   hw/ppc/spapr_pci.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
>> index f63182a03c41..ed4454bbf79e 100644
>> --- a/hw/ppc/spapr_pci.c
>> +++ b/hw/ppc/spapr_pci.c
>> @@ -1573,7 +1573,9 @@ static void spapr_pci_pre_plug(HotplugHandler 
>> *plug_handler,
>>        * hotplug, we do not allow functions to be hotplugged to a
>>        * slot that already has function 0 present
>>        */
>> -    if (plugged_dev->hotplugged && bus->devices[PCI_DEVFN(slotnr, 
>> 0)] &&
>> +    if (plugged_dev->hotplugged &&
>> +        !pci_is_vf(pdev) &&

I see there is history to this change. The reverted[1] virtio-net-pci 
SRIOV emulation support

needed this as the VFs were explicitly specified with -device 
virtio-net-pci,sriov-pf=X

property. I see the pre_plug handlers for the VFs cant be reached now 
with the reverted

code base for the other devices(nvme and igb) supporting the SRIOV 
emulation.


Do the VFs really reach this path in today's code base ? Other than the 
above

workflow, the pre_plug() handlers wont be called for VFs when the

echo X > /<sys-fs-pf-path>/sriov_numvfs inside the guest too. I don't 
see the

workflow(PF automatically creating VFs) to hit this path. Could you 
clarify how?


I see before the revert of virito-net-pci sriov use-case, the out of 
order VF hot|cold

plug post PF are prevented here. Even if we allowed VFs to continue 
here, PFs were

prevented in pcie_sriov_register_device() which is followed sequentially 
anyway. Now,

as the pcie_sriov_register_device() is no longer there, this check 
actually makes

sense as this would be the only place we avoid the out of order plugging.


On a side note, for testing this fulky on PPC, we need more work on Qemu 
today as the

open-sriov[2] is supported only on PowerVM.


Thanks,

Shivaprasad


Reference :

[1] - Atleast till commit b0fdaee5d1

[2] - 
https://lore.kernel.org/linuxppc-dev/20180105164552.36371-1-bryantly@linux.vnet.ibm.com/