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

[Laurent Vivier <lvivier@redhat.com>]

On 15/11/2016 19:01, Greg Kurz wrote:
> On Tue, 15 Nov 2016 16:07:40 +0100
> Laurent Vivier <lvivier@redhat.com> wrote:
> 
>> On 15/11/2016 16:03, Greg Kurz wrote:
>>> On Tue, 15 Nov 2016 14:48:30 +0000
>>> Stefan Hajnoczi <stefanha@gmail.com> 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 (stefanha@gmail.com) wrote:    
>>>>>>> On Tue, Nov 15, 2016 at 10:09 AM, Greg Kurz <groug@kaod.org> wrote:    
>>>>>>>> On Tue, 15 Nov 2016 10:53:35 +0100
>>>>>>>> Laurent Vivier <lvivier@redhat.com> 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.

>> It has been suggested a while to use an environment variable, like for
>> kvm-unit-tests, something like QTEST_ACCEL="kvm".
>>
> 
> Yeah, I think it would be better than "-accel kvm:tcg"
> 
>> Laurent
> 
> Cheers.
> 
> --
> Greg

Thanks,
Laurent