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Tue, 9 Feb 2021 16:42:40 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9D9914C04A; Tue, 9 Feb 2021 16:42:40 +0000 (GMT) Received: from localhost.localdomain (unknown [9.145.63.152]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 9 Feb 2021 16:42:40 +0000 (GMT) Subject: Re: [kvm-unit-tests PATCH] s390x: Workaround smp stop and store status race To: Thomas Huth , Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, david@redhat.com References: <20210209141554.22554-1-frankja@linux.ibm.com> <20210209170804.75d1fc9d@ibm-vm> From: Janosch Frank Message-ID: Date: Tue, 9 Feb 2021 17:42:40 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.737 definitions=2021-02-09_03:2021-02-09,2021-02-09 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 priorityscore=1501 lowpriorityscore=0 suspectscore=0 phishscore=0 adultscore=0 impostorscore=0 clxscore=1015 malwarescore=0 spamscore=0 mlxscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2102090081 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2/9/21 5:19 PM, Thomas Huth wrote: > 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 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 > I have no strong opinion on that although I'll need to have a look if our CI flags XPASS/XFAIL as fails.