On Mon, Sep 02, 2019 at 04:27:18PM +1000, David Gibson wrote: > On Fri, Aug 30, 2019 at 07:45:43PM +0200, Greg Kurz wrote: > > On Fri, 30 Aug 2019 17:34:13 +0100 > > Daniel P. Berrangé <berra...@redhat.com> wrote: > > > > > On Fri, Aug 30, 2019 at 06:13:45PM +0200, Laurent Vivier wrote: > > > > When we hotplug a CPU on memory-less/cpu-less node, the linux kernel > > > > crashes. > > > > > > > > This happens because linux kernel needs to know the NUMA topology at > > > > start to be able to initialize the distance lookup table. > > > > > > > > On pseries, the topology is provided by the firmware via the existing > > > > CPUs and memory information. Thus a node without memory and CPU cannot > > > > be > > > > discovered by the kernel. > > > > > > > > To avoid the kernel crash, do not allow to start pseries with empty > > > > nodes. > > > > > > This describes one possible guest OS. Is there any reasonable chance > > > that a non-Linux guest might be able to handle this situation correctly, > > > or do you expect any guest to have the same restriction ? > > That's... a more complicated question than you'd think. > > The problem here is it's not really obvious in PAPR how topology > information for nodes without memory should be described in the device > tree (which is the only way we given that information to the guest). > > It's possible there's some way to encode this information that would > make AIX happy and we just need to fix Linux to cope with that, but > it's not really clear what it would be. > > > I can try to grab an AIX image and give a try, but anyway this looks like > > a very big hammer to me... :-\ > > I'm not really sure why everyone seems to think losing zero-memory > node capability is such a big deal. It's never worked in practice on > POWER and we can always put it back if we figure out a sensible way to > do it.
I'm not that bothered - I just wanted to double check that we were not intentionally breaking a non-Linux guest OS that was known to work today. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
