Re: Unsupported delivery mode 7

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Nov 19, 2008 at 12:54:29PM +0000, Chris Webb wrote:
> We're running kvm-78 in production on Linux 2.6.27 x86_64 on dual quad-core
> Opteron 'Barcelona' machines. Our kvm modules are built from the kvm-78
> sources rather than the older version bundled with the kernel, and we're
> using the NPT features of the processors.
> 
> For the most part, everything is performing very well and running reliably.
> However, occasionally a guest will hang as it starts (or is reset) with a
> large number of messages of the form
> 
>   Unsupported delivery mode 7
> 
> in the dmesg. Following this, killing and relaunching the qemu process is
> usually sufficient to get a working guest.
> 
> I'm aware that our versions of the kvm kernel modules and userspace are not
> the latest release, but because we're running long-lived guests on behalf of
> clients, it's quite a major operation to upgrade. Does this look like a
> known bug which has already been fixed or should I try to reproduce it
> properly on a test machine with an ability to debug, use magic sysrq, etc?
> (It seems impossible to reproduce on my lower spec desktop machine, for what
> it's worth. Normally I'd reproduce kernel problems in a KVM virtual
> machine---but that's obviously not an option here!)
> 
> Am I right in suspecting it might be connected to interrupt delivery
> following page migration when a guest moves from one processor to another,
> and that a workaround might be to taskset guests to one or other physical
> CPU until we're able to upgrade to a more recent version of KVM?
> 
> Many thanks in advance for any advice anyone can offer.

On 2.6 guests this kernel option can workaround the bootup problem:

        no_timer_check  [X86-32,X86_64,APIC] Disables the code which tests for
                        broken timer IRQ sources.