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

Marc Zyngier
2015-02-16T08:57:50Z

On 15/02/15 19:03, Jan Kiszka wrote:
> On 2015-02-15 19:01, Jan Kiszka wrote:
>> On 2015-02-15 16:30, Marc Zyngier wrote:
>>> On Sun, Feb 15 2015 at 3:07:50 pm GMT, Jan Kiszka
>>> <jan.kiszka@web.de> wrote:
>>>> On 2015-02-15 15:59, Marc Zyngier wrote:
>>>>> 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.
>>>>
>>>> Ah, GICC != GICV - you are referring to host-side pending IRQs.
>>>> Any hints on how to get access to that register would
>>>> accelerate the analysis (ARM KVM code is still new to me).
>>>
>>> Map the GICC region in HYP using create_hyp_io_mapping (see
>>> vgic_v2_probe for an example of how we map GICH), and stash the
>>> read of GICC_HPPIR before leaving HYP mode (and before saving the
>>> guest timer).
>
>> Hacked on it until it started to work. The result delivered
>> initially are 0x002 or 0x01e. Then, when the guest gets stuck, I
>> have 0x01b most of the time (a few 0x01e arrive when there is a
>> real host irq). The virtual timer on speed?
>
>> Wait, there is also early printk for ARM, but it was off in my
>> guest! Turning it on confirms we have some problems here:
>
>> Architected timer frequency not available Division by zero in
>> kernel.
>
>> When in emulation mode, I get:
>
>> Architected cp15 timer(s) running at 62.50MHz (virt).
>
>> Digging deeper.
>
> U-Boot didn't initialize CNTFRQ on cores 1..3. Fixing this, the guest
> passes early boot reliably, now hangs much later (RCU stalls are
> detected by the guest).

Right, that explains a lot of things. Can you describe a bit more what
you're seeing now?

thanks,

M.
--
Jazz is not dead. It just smells funny...