Re: [Qemu-devel] [PATCH] kvm: fix Win2k boot without KVM

[Jan Kiszka]

On 2012-11-03 20:26, Blue Swirl wrote:
> On Sat, Nov 3, 2012 at 7:10 PM, Jan Kiszka <address@hidden> wrote:
>> On 2012-11-03 20:03, Jan Kiszka wrote:
>>> On 2012-11-03 19:56, Blue Swirl wrote:
>>>> On Sat, Nov 3, 2012 at 6:51 PM, Jan Kiszka <address@hidden> wrote:
>>>>> On 2012-11-03 19:49, Blue Swirl wrote:
>>>>>> Ignore accesses to VAPIC when kvmvapic is not enabled.
>>>>>>
>>>>>> Cc: Jan Kiszka <address@hidden>
>>>>>> Signed-off-by: Blue Swirl <address@hidden>
>>>>>> ---
>>>>>>  hw/kvmvapic.c |    7 ++++---
>>>>>>  1 files changed, 4 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/hw/kvmvapic.c b/hw/kvmvapic.c
>>>>>> index dc111ee..a97d532 100644
>>>>>> --- a/hw/kvmvapic.c
>>>>>> +++ b/hw/kvmvapic.c
>>>>>> @@ -612,6 +612,9 @@ static void vapic_write(void *opaque, hwaddr addr, 
>>>>>> uint64_t data,
>>>>>>      hwaddr rom_paddr;
>>>>>>      VAPICROMState *s = opaque;
>>>>>>
>>>>>> +    if (!kvm_irqchip_in_kernel()) {
>>>>>> +        return;
>>>>>> +    }
>>>>>>      cpu_synchronize_state(env);
>>>>>>
>>>>>>      /*
>>>>>> @@ -665,9 +668,7 @@ static void vapic_write(void *opaque, hwaddr addr, 
>>>>>> uint64_t data,
>>>>>>          break;
>>>>>>      default:
>>>>>>      case 4:
>>>>>> -        if (!kvm_irqchip_in_kernel()) {
>>>>>> -            apic_poll_irq(env->apic_state);
>>>>>> -        }
>>>>>> +        apic_poll_irq(env->apic_state);
>>>>>>          break;
>>>>>>      }
>>>>>>  }
>>>>>>
>>>>>
>>>>> NACK, I'm already debugging the true reason (related to code patching).
>>>>
>>>> This is a minimal fix that lets Win2k boot, now it does not work at
>>>> all. I think it should be applied for 1.3, it can be reverted when
>>>> (if) you find a better fix. There's no hurry though.
>>>
>>> If you want to disable it, flip apic.vapic for !kvm_enabled. Your patch
>>> affects user space APIC with KVM as well, though that is perfectly fine.
>>>
>>> But first of all give this some days as I just started.
>>
>> ...even more as this regression may not be related to the introduction
>> of the kvmvapic: My original test case for the kvmvapic under TCG,
>> WinXP, is now also broken, causing a segfault too.
>>
>> What I'm seeing is that tb_invalidate_phys_page_range in
>> patch_instruction no longer seems to detect that the currently executed
>> tb was just changed. Any ideas what may cause this are welcome.
> 
> My theory is that the kvmvapic ROM tries to make the PIO hypercalls,
> but the PIO devices in QEMU are not ready, maybe not initialized at
> all.

You are on the wrong track: All is set up, the first TPR accesses are
happening, and the kvmvapic is trying to patch them away. In TCG mode,
this requires a flush of the current TB afterward. And this somehow
fails, causing various issues as executing resumes at invalid addresses.

Jan

PS: A good hash is e.g. b34bd5e5c8f356ec206e5a306ee3a9b6f42c4315, long
after the kvmvapic merge.

PPS: Bisecting in QEMU is no fun - too many transient build breakages.

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