Re: [PATCH v2 5/5] hw/pci: ensure PCIE devices are plugged into only slot 0 of PCIE port

[Julia Suvorova]

On Thu, Jun 22, 2023 at 7:48 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Thu, Jun 22, 2023 at 05:46:40PM +0200, Julia Suvorova wrote:
> > On Thu, Jun 22, 2023 at 12:34 PM Ani Sinha <anisinha@redhat.com> wrote:
> > >
> > > PCI Express ports only have one slot, so PCI Express devices can only be
> > > plugged into slot 0 on a PCIE port. Enforce it.
> > >
> > > CC: jusual@redhat.com
> > > CC: imammedo@redhat.com
> > > Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2128929
> > > Signed-off-by: Ani Sinha <anisinha@redhat.com>
> > > ---
> > >  hw/pci/pci.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > > index bf38905b7d..5f25ab9f5e 100644
> > > --- a/hw/pci/pci.c
> > > +++ b/hw/pci/pci.c
> > > @@ -64,6 +64,7 @@ bool pci_available = true;
> > >  static char *pcibus_get_dev_path(DeviceState *dev);
> > >  static char *pcibus_get_fw_dev_path(DeviceState *dev);
> > >  static void pcibus_reset(BusState *qbus);
> > > +static bool pcie_has_upstream_port(PCIDevice *dev);
> > >
> > >  static Property pci_props[] = {
> > >      DEFINE_PROP_PCI_DEVFN("addr", PCIDevice, devfn, -1),
> > > @@ -1189,6 +1190,11 @@ static PCIDevice *do_pci_register_device(PCIDevice 
> > > *pci_dev,
> > >                     name);
> > >
> > >         return NULL;
> > > +    } else if (pcie_has_upstream_port(pci_dev) && PCI_SLOT(devfn)) {
> > > +        error_setg(errp, "PCI: slot %d is not valid for %s,"
> > > +                   " PCI express devices can only be plugged into slot 
> > > 0.",
> >
> > This is not technically correct, because downstream ports and root
> > ports are also PCIe devices, and they can have different slots under
> > upstream ports and RC. But this error will never be shown for them, so
> > it seems fine.
>
> Hmm. Confusing users is not nice ... I agree this might
> make people think they can not use root ports in slot !=0 either.
>
> Would you add "with an upstream port"?
> E.g. "PCI Express devices with an upstream port" ?

This whole upstream port conditioning is quite confusing.
How about "%parent device% only allows plugging into slot 0"?

Best regards, Julia Suvorova.

> >
> > Reviewed-by: Julia Suvorova <jusual@redhat.com>
> >
> >
> >
> >
> > > +                   PCI_SLOT(devfn), name);
> > > +        return NULL;
> > >      }
> > >
> > >      pci_dev->devfn = devfn;
> > > --
> > > 2.39.1
> > >
>