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

[Jan Kiszka <jan.kiszka@web.de>]

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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).

Jan

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