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 02:52:52PM +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.


> > 
> >>> 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