Re: arm: warning at virt/kvm/arm/vgic.c:1468

Marc Zyngier
2015-02-15T14:59:20Z

On Sun, Feb 15 2015 at 2:40:40 pm GMT, Jan Kiszka <jan.kiszka@web.de> wrote:
> On 2015-02-15 14:37, Marc Zyngier wrote:
>> On Sun, Feb 15 2015 at 8:53:30 am GMT, Jan Kiszka <jan.kiszka@web.de> wrote:
>>> I'm now throwing trace_printk at my broken KVM. Already found out that I
>>> get ARM_EXCEPTION_IRQ every few 10 µs. Not seeing any irq_* traces,
>>> though. Weird.
>>
>> This very much looks like a screaming interrupt. At such a rate, no
>> wonder your VM make much progress. Can you find out which interrupt is
>> screaming like this? Looking at GICC_HPPIR should help, but you'll have
>> to map the CPU interface in HYP before being able to access it there.
>
> OK... let me figure this out. I had this suspect as well - the host gets
> a VM exit for each injected guest IRQ?

Not exactly. There is a VM exit for each physical interrupt that fires
while the guest is running. Injecting an interrupt also causes a VM
exit, as we force the vcpu to reload its context.

> BTW, I also tried with in-kernel GIC disabled (in the kernel config),
> but I guess that's pointless. Linux seems to be stuck on a
> non-functional architectural timer then, right?

Yes. Useful for bringup, but nothing more.

>>
>> Do you have an form of power-management on this system?
>
> Just killed every config that has PM for FREQ in its name, but that
> makes no difference.

I still wonder if the 4+1 design on the K1 is not playing tricks behind
our back. Having talked to Ian Campbell earlier this week, he also can't
manage to run guests in Xen on this platform, so there's something
rather fishy here.

M.
--
Without deviation from the norm, progress is not possible.