Re: [PATCH v3] hw/pci/pci_bridge: ensure PCIe slots have only one slot

[Roman Kagan <rvkagan@yandex-team.ru>]

On Wed, Jul 20, 2022 at 12:04:58PM +0100, Daniel P. Berrangé wrote:
> On Wed, Jul 20, 2022 at 02:00:16PM +0300, Roman Kagan wrote:
> > On Wed, Jul 20, 2022 at 11:44:26AM +0100, Daniel P. Berrangé wrote:
> > > On Wed, Jul 20, 2022 at 01:25:55PM +0300, Roman Kagan wrote:
> > > > It's possible to create non-working configurations by attaching a device
> > > > to a derivative of PCIe slot (pcie-root-port, ioh3420, etc) and
> > > > specifying a slot number other that zero, e.g.:
> > > 
> > > What do you mean by 'non-working' in this case.  The guest OS boots
> > > OK, but I indeed don't see the device in the guest, but IIUC it was
> > > said that was just because Linux doesn't scan for a non-zero slot.
> > 
> > Right.  I don't remember if it was Linux or firmware or both but indeed
> > at least Linux guests don't see devices if attached to a PCIe slot at
> > addr != 0.  (Which is kinda natural for a thing called "slot", isn't it?)
> 
> If a configuration is a permissible per the hardware design / spec, then
> QEMU should generally allow it.  We don't want to constrain host side
> configs based on the current limitations of guest OS whose behaviour can
> change over time, or where a different guest OS may have a different POV.

OK I'll try to find out if PCIe slot devices may allow addresses
different from zero.  If anybody can advise on this that would be much
appreciated.

Thanks,
Roman.