On Wed, Oct 17, 2018 at 8:56 PM Andrea Bolognani <abologna@xxxxxxxxxx> wrote:
On Wed, 2018-10-17 at 10:50 +0800, Han Han wrote:
> In libvirt, I found pcie-expander-bus controller doesn't support pcie-to-pci-bridge and pcie-switch-upstream-port.
[...]
> # virsh -k0 -K0 define /tmp/c.xml
Aside: the -k and -K virsh options are documented as
-k | --keepalive-interval=NUM
keepalive interval in seconds, 0 for disable
-K | --keepalive-count=NUM
number of possible missed keepalive messages
So -k0 disables keepalive entirely, making -K0 unnecessary :)
Thanks for your advice.
> error: Failed to define domain from /tmp/c.xml
> error: XML error: The device at PCI address 0000:01:00.0 cannot be plugged into the PCI controller with index='1'. It requires a controller that accepts a pcie-to-pci-bridge.
[...]
> In function virDomainPCIAddressBusSetModel, I find pcie-expander-bus only supports pcie-root-port and dmi-to-pci-bridge
> 353 case VIR_DOMAIN_CONTROLLER_MODEL_PCIE_EXPANDER_BUS:
> 354 ┆ /* 32 slots, no hotplug, only accepts pcie-root-port or
> 355 ┆ ┆* dmi-to-pci-bridge
> 356 ┆ ┆*/
> 357 ┆ bus->flags = (VIR_PCI_CONNECT_TYPE_PCIE_ROOT_PORT |
> 358 ┆ ┆ ┆ ┆ ┆ VIR_PCI_CONNECT_TYPE_DMI_TO_PCI_BRIDGE);
> 359 ┆ bus->minSlot = 0;
> 360 ┆ bus->maxSlot = VIR_PCI_ADDRESS_SLOT_LAST;
> 361 ┆ break;
The above is consistent with pcie-root itself, which also doesn't
support plugging a pcie-to-pci-bridge directly into it but requires
a pcie-root <- pcie-root-port <- pcie-to-pci-bridge topology.
Now, I don't quite recall *why* that is the case - perhaps Laine
does? - but I'm sure we had very compelling reasons O:-)
> But it works in qemu:
> # /usr/libexec/qemu-kvm -machine q35 -m 1024 -device pxb-pcie,bus_nr=250,id=pci.1,bus=pcie.0,addr=0x4 -device pcie-pci-bridge,id=pci.250,bus=pci.1,addr=0x0 -device pcie-pci-bridge,id=pci.251,bus=pci.1,addr=0x1 -spice port=5902,addr=0.0.0.0,disable-ticketing /var/lib/libvirt/images/q35.qcow2
It should be noted that QEMU in general allows users to make pretty
unwise device placement choices without so much of a warning, so I
would not take the above as proof the pcie-to-pci-bridge should be
allowed to plug into pcie-expander-bus (or pcie-root) directly :)
If pcie<-pcie-expander-bus<-(pcie-to-pci-bridge | pcie-switch-upstream-port) is an unwise device placement, we'd better to add the reason to code comments or commit msg or documents.
--
Andrea Bolognani / Red Hat / Virtualization
--
Best regards,
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