Re: [kvm-unit-tests PATCH] s390x: Workaround smp stop and store status race

[Thomas Huth <thuth@redhat.com>]

On 09/02/2021 17.14, Janosch Frank wrote:
> On 2/9/21 5:08 PM, Claudio Imbrenda wrote:
>> On Tue,  9 Feb 2021 09:15:54 -0500
>> Janosch Frank <frankja@linux.ibm.com> wrote:
>>
>>> KVM and QEMU handle a SIGP stop and store status in two steps:
>>> 1) Stop the CPU by injecting a stop request
>>> 2) Store when the CPU has left SIE because of the stop request
>>>
>>> The problem is that the SIGP order is already considered completed by
>>> KVM/QEMU when step 1 has been performed and not once both have
>>> completed. In addition we currently don't implement the busy CC so a
>>> kernel has no way of knowing that the store has finished other than
>>> checking the location for the store.
>>>
>>> This workaround is based on the fact that for a new SIE entry (via the
>>> added smp restart) a stop with the store status has to be finished
>>> first.
>>>
>>> Correct handling of this in KVM/QEMU will need some thought and time.
>>
>> do I understand correctly that you are here "fixing" the test by not
>> triggering the KVM bug? Shouldn't we try to trigger as many bugs as
>> possible instead?
> 
> This is not a bug, it's missing code :-)
> 
> We trigger a higher number of bugs by running tests and this workaround
> does exactly that by letting Thomas use the smp test in the CI again.

Alternatively, we could use report_xfail here to make the test pass, but 
still have the problem reported so that we do not forget to fix it later.

  Thomas