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

[Michael S. Tsirkin]

On Fri, Jun 30, 2023 at 04:07:32PM +0530, Ani Sinha wrote:
> 
> 
> > On 30-Jun-2023, at 3:30 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > 
> > On Fri, Jun 30, 2023 at 02:52:52PM +0530, Ani Sinha wrote:
> >> 
> >> 
> >>> 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.
> > 
> > Because next parameter in pcie_ari_init does not match.
> 
> OK send me a command line that I can test it with. I can’t come up with a 
> case that actually works in practice.


you need to patch igb to pass 2 as next parameter.
maybe add a property to make it easier to play with.

> > 
> > 
> >>> 
> >>>>> 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