Re: [PATCH 4/6] qemu: assign PCI address to device pvpanic-pci

On Wed, Feb 08, 2023 at 12:49:03PM +0100, Kristina Hanicova wrote: So, this is correct, because pvpanic-pci is indeed a conventional PCI device (as opposed to a PCI Express device). However, when used with a PCIe-based machine such as aarch64/virt, these flags result in the device being plugged into a pcie-pci-bridge, which in turn is plugged into a pcie-root-port, itself plugged into pcie.0. While this seems to work fine, it's also kind of a waste of PCI controllers. For a "system" device such as pvpanic-pci, I think plugging directly into pcie.0 might be more appropriate. This is particularly true of x86/q35, where with the current implementation switching from ISA pvpanic to pvpanic-pci would result in adding two extra PCI controllers. So I think this would be a good fit for the VIR_PCI_CONNECT_INTEGRATED flag that I've added a while ago for use with virtio-iommu. While this would technically result in libvirt being more restrictive than QEMU in what PCI addresses it accepts for pvpanic-pci, I don't think this would limit users in practice, and in the default case (libvirt automatically picking the address) the resulting configuration would be preferable. We can always decide to relax this restriction later down the line, if it turns out to really be a limiting factor. Eric, what do you think about this idea? (There's one caveat: VIR_PCI_CONNECT_INTEGRATED doesn't seem to work with pciFlags at the moment O:-) It works fine with pcieFlags and virtioFlags. I'll try to figure out why that's the case.) -- Andrea Bolognani / Red Hat / Virtualization