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Wed, 5 Jul 2023 11:19:42 +0000 (GMT) From: Claudio Imbrenda To: kvm@vger.kernel.org Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, frankja@linux.ibm.com, mhartmay@linux.ibm.com, nsg@linux.ibm.com, borntraeger@de.ibm.com, nrb@linux.ibm.com Subject: [PATCH v2 1/2] KVM: s390: pv: simplify shutdown and fix race Date: Wed, 5 Jul 2023 13:19:36 +0200 Message-ID: <20230705111937.33472-2-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230705111937.33472-1-imbrenda@linux.ibm.com> References: <20230705111937.33472-1-imbrenda@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: ZcUwoCgOVudp_fkWKBKrwC1ctna5ueZb X-Proofpoint-GUID: ZcUwoCgOVudp_fkWKBKrwC1ctna5ueZb X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.591,FMLib:17.11.176.26 definitions=2023-07-05_02,2023-07-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxlogscore=975 mlxscore=0 malwarescore=0 phishscore=0 impostorscore=0 bulkscore=0 priorityscore=1501 spamscore=0 lowpriorityscore=0 adultscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2305260000 definitions=main-2307050097 X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1770580561420784788?= X-GMAIL-MSGID: =?utf-8?q?1770580561420784788?= Simplify the shutdown of non-protected VMs. There is no need to do complex manipulations of the counter if it was zero. This also fixes a very rare race which caused pages to be torn down from the address space with a non-zero counter even on older machines that don't support the UVC instruction, causing a crash. Reported-by: Marc Hartmayer Fixes: fb491d5500a7 ("KVM: s390: pv: asynchronous destroy for reboot") Signed-off-by: Claudio Imbrenda Reviewed-by: Nico Boehr --- arch/s390/kvm/pv.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c index 3ce5f4351156..899f3b8ac011 100644 --- a/arch/s390/kvm/pv.c +++ b/arch/s390/kvm/pv.c @@ -411,8 +411,12 @@ int kvm_s390_pv_deinit_cleanup_all(struct kvm *kvm, u16 *rc, u16 *rrc) u16 _rc, _rrc; int cc = 0; - /* Make sure the counter does not reach 0 before calling s390_uv_destroy_range */ - atomic_inc(&kvm->mm->context.protected_count); + /* + * Nothing to do if the counter was already 0. Otherwise make sure + * the counter does not reach 0 before calling s390_uv_destroy_range. + */ + if (!atomic_inc_not_zero(&kvm->mm->context.protected_count)) + return 0; *rc = 1; /* If the current VM is protected, destroy it */