Re: [libvirt] [Qemu-devel] PCI(e): Documentation "io-reserve" and related properties?

On Thu, 2019-06-06 at 14:20 -0400, Michael S. Tsirkin wrote: Is it fair to say that setting io-reserve=0 for a pcie-root-port would be a way to implement the requirements set forth in https://bugzilla.redhat.com/show_bug.cgi?id=1408810 ? I tested this on aarch64 and it seems to work as expected, but then again without documentation it's hard to tell. More specifically, I created an aarch64/virt guest with several pcie-root-ports and it couldn't boot much further than GRUB when the number of ports exceeded 24, but as soon as I added the io-reserve=0 option I could get the same guest to boot fine with 32 or even 64 pcie-root-ports. I'm attaching the boot log for reference: there are a bunch of messages about the topic but they would appear to be benign. Hotplug seemed to work too: I tried with a single virtio-net-pci and I could access the network. My understanding is that PCIe devices are required to work without IO space, so this behavior matches my expectations. I wonder, though, what would happen if I had something like -device pcie-root-port,io-reserve=0,id=pci.1 -device pcie-pci-bridge,bus=pci.1 Would I be able to hotplug conventional PCI devices into the pcie-pci-bridge, or would the lack of IO space reservation for the pcie-root-port cause issues with that? -- Andrea Bolognani / Red Hat / Virtualization