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 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.

> > 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 ...

> > and the benefit
> > is not guaranteed.
> > 
> > -- 
> > MST
> >