Re: [Qemu-devel] QEMU postcopy-test failing on ppc64

[Thomas Huth]

On 15.11.2016 21:02, Greg Kurz wrote:
> On Tue, 15 Nov 2016 19:24:24 +0100
> Laurent Vivier <address@hidden> wrote:
> 
>> On 15/11/2016 19:01, Greg Kurz wrote:
>>> On Tue, 15 Nov 2016 16:07:40 +0100
>>> Laurent Vivier <address@hidden> wrote:
>>>   
>>>> On 15/11/2016 16:03, Greg Kurz wrote:  
>>>>> On Tue, 15 Nov 2016 14:48:30 +0000
>>>>> Stefan Hajnoczi <address@hidden> wrote:
>>>>>     
>>>>>> On Tue, Nov 15, 2016 at 01:58:38PM +0100, Laurent Vivier wrote:    
>>>>>>>
>>>>>>>
>>>>>>> On 15/11/2016 13:20, Dr. David Alan Gilbert wrote:      
>>>>>>>> * Stefan Hajnoczi (address@hidden) wrote:      
>>>>>>>>> On Tue, Nov 15, 2016 at 10:09 AM, Greg Kurz <address@hidden> wrote:   
>>>>>>>>>    
>>>>>>>>>> On Tue, 15 Nov 2016 10:53:35 +0100
>>>>>>>>>> Laurent Vivier <address@hidden> wrote:
>>>>>>>>>>      
>>>>>>>>>>> On 14/11/2016 21:52, Stefan Hajnoczi wrote:      
>>>>>>>>>>>> I hit a failure running "make check" on ppc64 for the first time.  
>>>>>>>>>>>> Ideas?
>>>>>>>>>>>>
>>>>>>>>>>>> Stefan
>>>>>>>>>>>>
>>>>>>>>>>>> commit 682df581c65ed2c1b9e77093e332214ecaa1ee93
>>>>>>>>>>>>
>>>>>>>>>>>>   GTESTER check-qtest-ppc64
>>>>>>>>>>>> Memory content inconsistency at 5af4000 first_byte = 1b last_byte 
>>>>>>>>>>>> = 1a
>>>>>>>>>>>> current = 7c hit_edge = 1
>>>>>>>>>>>> Memory content inconsistency at 5af5000 first_byte = 1b last_byte 
>>>>>>>>>>>> = 7c
>>>>>>>>>>>> current = 1b hit_edge = 1
>>>>>>>>>>>> Memory content inconsistency at 5e59000 first_byte = 1b last_byte 
>>>>>>>>>>>> = 1b
>>>>>>>>>>>> current = 1a hit_edge = 1
>>>>>>>>>>>> **
>>>>>>>>>>>> ERROR:tests/postcopy-test.c:345:check_guests_ram: 'bad' should be 
>>>>>>>>>>>> FALSE
>>>>>>>>>>>> GTester: last random seed: R02S9d79166a1ca7e21940a0f4b0b1255d5b
>>>>>>>>>>>>      
>>>>>>>>>>>
>>>>>>>>>>> Are you using KVM PR?
>>>>>>>>>>>
>>>>>>>>>>> it  was working fine with TCG and KVM HV.
>>>>>>>>>>>
>>>>>>>>>>> Apparently, USERFAULTFD doesn't work with KVM PR.
>>>>>>>>>>>
>>>>>>>>>>> I've already seen this kind of error with nested KVM on Power:
>>>>>>>>>>> guest in guest with KVM PR in host.
>>>>>>>>>>>
>>>>>>>>>>> This problem was reported on IRC by Greg if I remember correctly 
>>>>>>>>>>> (CC:)
>>>>>>>>>>>      
>>>>>>>>>>
>>>>>>>>>> Yeah I hit this when running make check in a PPC64 BE guest which
>>>>>>>>>> has kvm_pr loaded. I did not find time to investigate though... I've
>>>>>>>>>> switched to run make check on bare metal POWER7 instead.      
>>>>>>>>>
>>>>>>>>> Right, it's POWER7 PPC64 BE with kvm_pr.
>>>>>>>>>
>>>>>>>>> If this should be fixed for QEMU 2.8 please add it to
>>>>>>>>> http://qemu-project.org/Planning/2.8 and I'll track it (i.e. won't
>>>>>>>>> release before it's resolved).
>>>>>>>>>
>>>>>>>>> If this is a known issue that will be in QEMU 2.8 please add it to
>>>>>>>>> http://qemu-project.org/ChangeLog/2.8#Known_issues.      
>>>>>>>>
>>>>>>>> I don't think it's new with 2.8 (Laurent?) and I think it's actually
>>>>>>>> a kernel issue that needs fixing.      
>>>>>>>
>>>>>>> I's not a regression and I think it's a kernel issue.
>>>>>>>
>>>>>>> As it has never worked with KVM PR and can't be fixed at QEMU level, we
>>>>>>> can't solve it for 2.8 (no tracking).
>>>>>>>
>>>>>>> I'm going to update the know issues for 2.8.
>>>>>>> [and I'm going to try to understand what really happens]      
>>>>>>
>>>>>> Should the test be skipped on KVM PR?
>>>>>>
>>>>>> It's a shame that make check fails.
>>>>>>    
>>>>>
>>>>> Yeah I agree this is lame but KVM PR isn't very cherished these days...
>>>>>
>>>>> Since postcopy-test runs QEMU with -accel kvm:tcg, a possible workaround 
>>>>> is
>>>>> to kick KVM out of the environment you're running make check in.    
>>>>
>>>> Moreover, using "-accel kvm:tcg" induces an error when the test is
>>>> running in cross-arch case (ppc on intel, or intel on ppc).
>>>>  
>>>
>>> You're talking about the '"kvm" accelerator not found' error ?  
>>
>> Yes
>>
>>>   
>>>> But I think postcopy is typically something we should test with KVM, not
>>>> TCG, as there are some kernel dependencies (USERFAULTFD).
>>>>  
>>>
>>> I agree it should be tested with KVM when applicable but I don't understand
>>> the 'not TCG' since it is the only way to test when you don't have access
>>> to specific hardware...  
>>
>> I agree; What I mean is we must test this preferably with KVM because it
>> is more likely to have a problem with KVM than with TCG because of the
>> MMU virtualization.
>>
> 
> Fair enough but this doesn't address the problem we currently have: a broken
> KVM can cause make check to fail...

Thinking about this again ... maybe the code to exercise KVM should
rather go into kvm-unit-tests instead of being part of the QEMU tests?

 Thomas