Re: [PATCH v6 5/5] hw/pci: ensure PCIE devices are plugged into only slot 0 of PCIE port

[Ani Sinha]

> On 30-Jun-2023, at 2:13 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> 
> On Fri, Jun 30, 2023 at 02:06:59PM +0530, Ani Sinha wrote:
>> 
>> 
>>> On 30-Jun-2023, at 2:02 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
>>> 
>>> On Fri, Jun 30, 2023 at 01:11:33PM +0530, Ani Sinha wrote:
>>>>> 
>>>>> Thus the check for unoccupied function 0 needs to use pci_is_vf() instead 
>>>>> of checking ARI capability, and that can happen in 
>>>>> do_pci_register_device().
>>>>> 
>>>>>> Also where do you propose we move the check?
>>>>> 
>>>>> In pci_qdev_realize(), somewhere after pc->realize() and before option 
>>>>> ROM loading.
>>>> 
>>>> Hmm, I tried this. The issue here is something like this would be now 
>>>> allowed since the PF has ARI capability:
>>>> 
>>>> -device pcie-root-port,id=p -device igb,bus=p,addr=0x2.0x0
>>>> 
>>>> The above should not be allowed and when used, we do not see the igb 
>>>> ethernet device from the guest OS.
>>> 
>>> I think it's allowed because it expects you to hotplug function 0 later,
>> 
>> This is about the igb device being plugged into the non-zero slot of the 
>> pci-root-port. The guest OS ignores it.
> 
> yes but if you later add a device with ARI and with next field pointing
> slot 2 guest will suddently find both.

Hmm, I tried this:

-device pcie-root-port,id=p \
-device igb,bus=p,addr=0x2.0x0 \
-device igb,bus=p,addr=0x0.0x0 \

The guest only found the second igb device not the first. You can try too.

> 
>>> no?
>>> 
>>> I am quite worried about all this work going into blocking
>>> what we think is disallowed configurations. We should have
>>> maybe blocked them originally, but now that we didn't
>>> there's a non zero chance of regressions,
>> 
>> Sigh,
> 
> There's value in patches 1-4 I think - the last patch helped you find
> these. so there's value in this work.
> 
>> no medals here for being brave :-)
> 
> Try removing support for a 3.5mm jack next. Oh wait ...

Indeed. Everyone uses bluetooth these days. I for one is happy that the jack is 
gone (and they were bold enough to do it while Samsung and others still carry 
the useless port ) :-)
 
> 
>>> and the benefit
>>> is not guaranteed.
>>> 
>>> -- 
>>> MST