In a full domain config, libvirt allows overriding the normal PCI vs. PCI Express rules when a device address is explicitly provided (so, e.g., you can force a legacy PCI device to plug into a PCIe port, although libvirt would never do that on its own). However, due to a bug libvirt doesn't give this same leeway when hotplugging devices. On top of that, current libvirt assumes that *all* devices are legacy PCI. The result of all this is that it's impossible to hotplug a device into a PCIe port, even if you manually add the PCI address. This can all be traced to the function virDomainPCIAddressEnsureAddr(), and the fact that it calls virDomainPCIaddressReserveSlot() for manually set addresses, and that function hardcodes the argument "fromConfig" to false (meaning "this address was auto-assigned, so it should be subject to stricter validation"). Since virDomainPCIAddressReserveSlot() is just a one line simple wrapper around virDomainPCIAddressReserveAddr() (adding in a hardcoded reserveEntireSlot = true and fromConfig = false), all that's needed to solve the problem with no unwanted side effects is to replace that call for virDomainPCIAddressReserveSlot() with a direct call to virDomainPCIAddressReserveAddr(), but with reserveEntireSlot = true, fromConfig = true. That's what this patch does. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1337490 --- src/conf/domain_addr.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/conf/domain_addr.c b/src/conf/domain_addr.c index 79c024f..93026c2 100644 --- a/src/conf/domain_addr.c +++ b/src/conf/domain_addr.c @@ -507,7 +507,8 @@ virDomainPCIAddressEnsureAddr(virDomainPCIAddressSetPtr addrs, addrStr, flags, true)) goto cleanup; - ret = virDomainPCIAddressReserveSlot(addrs, &dev->addr.pci, flags); + ret = virDomainPCIAddressReserveAddr(addrs, &dev->addr.pci, flags, + true, true); } else { ret = virDomainPCIAddressReserveNextSlot(addrs, dev, flags); }