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.: > > > > -device pcie-root-port,id=s0,... \ > > -device virtio-blk-pci,bus=s0,addr=4,... > > > > Make QEMU reject such configurations and only allow addr=0 on the > > secondary bus of a PCIe slot. > > 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?) > That wouldn't be a broken config from QEMU's POV though, merely a > guest OS limitation ? Strictly speaking it wouldn't, indeed. But we've had created such a configuration (due to a bug in our management layer) and spent non-negligible time trying to figure out why the attached device didn't appear in the guest. So I thought it made sense to reject a configuration which is known to confuse guests. Doesn't it? Thanks, Roman.
