[libvirt-users] assigning PCI addresses with bus > 0x09

[Riccardo Ravaioli]

On Thu, 20 Dec 2018 at 15:39, Laine Stump <laine at redhat.com> wrote:

> [...]
> I think you're right. Each bus requires some amount of IO space, and I
> thought I recalled someone saying that all of the available IO space is
> exhausted after 7 or 8 buses. This was in relation to PCIe, where each
> root port is a bus, and can potentially take up IO space, so possibly in
> that context they were talking about the buses *after* the root bus and
> pcie-pci-bridge, which would bring us back to the same number you're
> getting.
>
> For PCIe our solution was to turn off IO space usage on the
> pcie-root-ports, but you can't do that for conventional PCI buses, since
> the devices might actually need IO space to function properly and the
> standard requires that you provide it.
>

Ok, that makes sense.


> > The real question though is why you need to create sooooo many PCI buses.
> > Each bus can do 31 devices.  Do you really need to have more than 279
> > devices in your VM ?
>
> And if you do need more than 279 devices, do they all need to be
> hot-pluggable? If not, then you can put up to 8 devices on each slot
> (functions 0 - 7).
>

True. I'll use the function field too, then.

Thanks a lot!

Riccardo
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