Re: [libvirt] [PATCH 08/11] conf: Prefer pcie-to-pci-bridge to dmi-to-pci-bridge

Both pcie-to-pci-bridge and dmi-to-pci-bridge can be used to create a traditional PCI topology in a pure PCIe guest such as those using the x86_64/q35 or aarch64/virt machine type; however, the former should be preferred, as it doesn't need to obey limitation of real hardware and is completely architecture-agnostic. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1520821 Signed-off-by: Andrea Bolognani <abologna(a)redhat.com&gt; --- src/conf/domain_addr.c | 59 +++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 49 insertions(+), 10 deletions(-) diff --git a/src/conf/domain_addr.c b/src/conf/domain_addr.c index b0709f8295..8964973e03 100644 --- a/src/conf/domain_addr.c +++ b/src/conf/domain_addr.c @@ -416,6 +416,7 @@ virDomainPCIAddressSetGrow(virDomainPCIAddressSetPtr addrs, size_t i; int model; bool needDMIToPCIBridge = false; + bool needPCIeToPCIBridge = false; add = addr->bus - addrs->nbuses + 1; if (add <= 0) @@ -436,27 +437,41 @@ virDomainPCIAddressSetGrow(virDomainPCIAddressSetPtr addrs, model = VIR_DOMAIN_CONTROLLER_MODEL_PCI_BRIDGE; /* if there aren't yet any buses that will accept a - * pci-bridge, and the caller is asking for one, we'll need to - * add a dmi-to-pci-bridge first. + * pci-bridge, but we need one for the device's PCI address + * to make sense, it means the guest only has a PCIe topology + * configured so far, and we need to create a traditional PCI + * topology to accomodate the new device. */ needDMIToPCIBridge = true; + needPCIeToPCIBridge = true; for (i = 0; i < addrs->nbuses; i++) { if (addrs->buses[i].flags & VIR_PCI_CONNECT_TYPE_PCI_BRIDGE) { needDMIToPCIBridge = false; + needPCIeToPCIBridge = false; break; } } - if (needDMIToPCIBridge && add == 1) { + + /* Prefer pcie-to-pci-bridge, fall back to dmi-to-pci-bridge */ + if (addrs->isPCIeToPCIBridgeSupported) + needDMIToPCIBridge = false; + else + needPCIeToPCIBridge = false;

+ + if ((needDMIToPCIBridge || needPCIeToPCIBridge) && add == 1) { /* We need to add a single pci-bridge to provide the bus * our legacy PCI device will be plugged into; however, we * have also determined that there isn't yet any proper - * place to connect that pci-bridge we're about to add (on - * a system with pcie-root, that "proper place" would be a - * dmi-to-pci-bridge". So, to give the pci-bridge a place - * to connect, we increase the count of buses to add, - * while also incrementing the bus number in the address - * for the device (since the pci-bridge will now be at an - * index 1 higher than the caller had anticipated). + * place to connect that pci-bridge we're about to add, + * which means we're dealing with a pure PCIe guest. We + * need to create a traditional PCI topology, and for that + * we have two options: dmi-to-pci-bridge + pci-bridge or + * pcie-root-port + pcie-to-pci-bridge (the latter of which + * is pretty much a pci-bridge as far as devices attached + * to it are concerned and as such makes the pci-bridge + * unnecessary). Either way, there's going to be one more + * controller than initially expected, and the 'bus' part + * of the device's address will need to be bumped. */ add++; addr->bus++; @@ -525,6 +540,30 @@ virDomainPCIAddressSetGrow(virDomainPCIAddressSetPtr addrs, } } + if (needPCIeToPCIBridge) { + /* We need a pcie-root-port to plug pcie-to-pci-bridge into; however, + * qemuDomainAssignPCIAddresses() will, in some cases, create a dummy + * PCIe device and reserve an address for it in order to leave the + * user with an empty pcie-root-port ready for hotplugging, and if + * we didn't do anything other than adding the pcie-root-port here + * it would be used for that, which we don't want. So we change the + * connect flags to make sure only the pcie-to-pci-bridge will be + * connected to the pcie-root-port we just added, and another one + * will be allocated for the dummy PCIe device later on. + */ + if (virDomainPCIAddressBusSetModel(&addrs->buses[i], + VIR_DOMAIN_CONTROLLER_MODEL_PCIE_ROOT_PORT) < 0) { + return -1; + } + addrs->buses[i].flags = VIR_PCI_CONNECT_TYPE_PCIE_TO_PCI_BRIDGE; + i++; + + if (virDomainPCIAddressBusSetModel(&addrs->buses[i++], + VIR_DOMAIN_CONTROLLER_MODEL_PCIE_TO_PCI_BRIDGE) < 0) { + return -1; + } + } + for (; i < addrs->nbuses; i++) { if (virDomainPCIAddressBusSetModel(&addrs->buses[i], model) < 0) return -1;