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Mon, 7 Dec 2020 20:16:37 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C7A2FA4040; Mon, 7 Dec 2020 20:16:36 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.4.19]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 7 Dec 2020 20:16:36 +0000 (GMT) Subject: Re: [PATCH v4] self_tests/kvm: sync_regs test for diag318 To: Collin Walling , kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: frankja@linux.ibm.com, david@redhat.com, thuth@redhat.com, cohuck@redhat.com, pbonzini@redhat.com, imbrenda@linux.ibm.com References: <20201207154125.10322-1-walling@linux.ibm.com> <2ea47a0e-40fb-35bc-5819-63a9e7b2ec59@de.ibm.com> <87bf5fb7-26bf-f757-1efa-d2a49bde5188@de.ibm.com> <501fe03a-c245-73f3-4715-1327cc73a712@linux.ibm.com> From: Christian Borntraeger Message-ID: Date: Mon, 7 Dec 2020 21:16:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <501fe03a-c245-73f3-4715-1327cc73a712@linux.ibm.com> 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=2.50.10434:6.0.343,18.0.737 definitions=2020-12-07_16:2020-12-04,2020-12-07 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 mlxscore=0 malwarescore=0 priorityscore=1501 impostorscore=0 spamscore=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 mlxlogscore=999 adultscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012070125 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 07.12.20 21:13, Collin Walling wrote: > On 12/7/20 3:09 PM, Christian Borntraeger wrote: >> >> >> On 07.12.20 21:06, Collin Walling wrote: >>> On 12/7/20 2:32 PM, Christian Borntraeger wrote: >>>> On 07.12.20 16:41, Collin Walling wrote: >>>>> The DIAGNOSE 0x0318 instruction, unique to s390x, is a privileged call >>>>> that must be intercepted via SIE, handled in userspace, and the >>>>> information set by the instruction is communicated back to KVM. >>>>> >>>>> To test the instruction interception, an ad-hoc handler is defined which >>>>> simply has a VM execute the instruction and then userspace will extract >>>>> the necessary info. The handler is defined such that the instruction >>>>> invocation occurs only once. It is up to the caller to determine how the >>>>> info returned by this handler should be used. >>>>> >>>>> The diag318 info is communicated from userspace to KVM via a sync_regs >>>>> call. This is tested During a sync_regs test, where the diag318 info is >>>>> requested via the handler, then the info is stored in the appropriate >>>>> register in KVM via a sync registers call. >>>>> >>>>> If KVM does not support diag318, then the tests will print a message >>>>> stating that diag318 was skipped, and the asserts will simply test >>>>> against a value of 0. >>>>> >>>>> Signed-off-by: Collin Walling >>>> >>>> Interestingly enough, this testcase actually trigger a bug: >>>> While we gracefully handle this (no crash) >>>> debugfs: Directory 'kvm-200206' with parent 's390dbf' already present! >>>> is certainly not ideal.... >>>> >>> >>> Odd... I wonder what triggered this behavior? >>> >>> I run my tests with a simple command: >>> >>> make summary=0 TARGETS=kvm kselftest >>> >>> This must have something to do with spinning up another VM to get the >>> diag318 data. I think if I have the sync_regs test call the diag handler >>> first, and then have the sync regs create a VM, that might solve that >>> issue... >> >> Yes, the s390dbf code will try to create a file named kvm-%pid. With >> 2 VMs the 2nd one fails. Luckily the kvm will be created anyway and >> also the shutdown seems to be fine, still.... >> >>> >>> May I ask how you encountered this bug so I may replicate in on my end? >> >> I just did >> make TARGETS=kvm selftests >> >> and then the error is on dmesg. >> > > Thanks. v5 with fix incoming. I think the test is actually fine and we should rather fix the kvm module to gracefully handle a userspace that starts up 2 or more guests.