On Wed, 2016-07-20 at 14:17 +0100, Daniel P. Berrange wrote:
Commit 8156493d8db9 changed libvirt so that '-device pci-ohci' would be used instead of '-usb' on ppc64 when no specific USB controller model had been specified in the guest configuration. While the device that ends up being presented by the guest is exactly the same, '-usb' causes it to be assigned to PCI address 00:00.0 while '-device pci-ohci', being subject to the regular PCI address assignment logic, will be at a different address. This PCI address mismatch breaks migration of existing guests to new libvirt versions. Luckily, when QEMU has switched its default '-usb' controller from pci-ohci to nec-usb-xhci (QEMU commit 57040d451315), it has done so without affecting older machine types, which means we can keep using '-usb' without risking guest ABI breakage. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1357468 --- src/qemu/qemu_command.c | 8 +++++--- tests/qemuxml2argvdata/qemuxml2argv-ppc64-usb-controller.args | 2 +- tests/qemuxml2argvdata/qemuxml2argv-pseries-usb-default.args | 2 +- 3 files changed, 7 insertions(+), 5 deletions(-) Ján pointed out that applying this would un-break migration for ppc64 guests created before 8156493d8db9, but at the same time break migration for those created since, eg. in
On Tue, 2016-07-19 at 16:17 +0200, Andrea Bolognani wrote: the last ~6 months. I'm kinda out of ideas here, so if anyone has a brilliant plan to make migration work for both old and new guests, please do share :) It seems that we could solve this by just changing the logic in qemuDomainAssignDevicePCISlots() so that when it is auto-assigning addresses, it always uses 00:00.0 for the USB controller when guest arch is ppc64. Existing guests deployed from a libvirt version using -device won't be affected, because we'll have recorded a PCI address for that in the XML and continue to use that. ie the auto-allocation logic won't run for them. Existing guests deployed from a libvirt version using -usb should
On Tue, Jul 19, 2016 at 07:04:36PM +0200, Andrea Bolognani wrote: then get the fixed PCI address of 00:00.0 when they upgrade to the fix libvirt (assuming they didn't get run with a broken libvirt in between).
Mh, that could actually work! Thanks :) I'll try to cook up a patch tomorrow.
Regardless though, I'm very much against any change that tales us back to using -usb. This is long since obsolete syntax we should aim to never use - bringing ppc inline with other arches using -device is very much desirable.
Agreed - that was the reasoning behind the original, sadly flawed, attempt to get rid of it. -- Andrea Bolognani / Red Hat / Virtualization