From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A95BAC12002 for ; Wed, 21 Jul 2021 14:46:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8824B61221 for ; Wed, 21 Jul 2021 14:46:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238364AbhGUOFa (ORCPT ); Wed, 21 Jul 2021 10:05:30 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:9598 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S232977AbhGUOF3 (ORCPT ); Wed, 21 Jul 2021 10:05:29 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 16LEXGE6016086; Wed, 21 Jul 2021 10:46:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=date : from : to : cc : subject : message-id : in-reply-to : references : mime-version : content-type : content-transfer-encoding; s=pp1; bh=idOSKcIpSGAJCFkAxhVfxNrXuZDZVWjSg4IXQKAQfKE=; b=Zvd1yKxfs0V2BAD32UYslyzCjxyZQupea4xRTwXP/DNmFaLTCfLyykyQ90YXJ3vI89Mb wc/X+fts0l8tWZOXiYAPk3QDrVUiPqUMj779KZZ09GTosmCf2xbfyp5AX2eG6neqMA9/ z1j7YKgK3bKnOuVXJWh7JkhBT3/cMUZkZGYV1sdSEnjw4rcH81qoS91YxW5lRyDaaIKL eheUWMxRZ3sx6vB7CDjcEM3EvBCIdYqwcLXyOtGfweuxRrCflWlUO7ulAO9d4Uz8Rivp zJKF42RWdIvmEoGvlxn1Te3X5VABDt5xMox1AMWElNenHZI2YRoaAspXjzS4kyefNz6H 2g== Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com with ESMTP id 39xkeemes9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 21 Jul 2021 10:46:03 -0400 Received: from m0098419.ppops.net (m0098419.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.43/8.16.0.43) with SMTP id 16LEXlQs018761; Wed, 21 Jul 2021 10:46:02 -0400 Received: from ppma03ams.nl.ibm.com (62.31.33a9.ip4.static.sl-reverse.com [169.51.49.98]) by mx0b-001b2d01.pphosted.com with ESMTP id 39xkeemek3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 21 Jul 2021 10:46:02 -0400 Received: from pps.filterd (ppma03ams.nl.ibm.com [127.0.0.1]) by ppma03ams.nl.ibm.com (8.16.1.2/8.16.1.2) with SMTP id 16LEhiTh023345; Wed, 21 Jul 2021 14:45:57 GMT Received: from b06cxnps3075.portsmouth.uk.ibm.com (d06relay10.portsmouth.uk.ibm.com [9.149.109.195]) by ppma03ams.nl.ibm.com with ESMTP id 39upu89xn4-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 21 Jul 2021 14:45:57 +0000 Received: from d06av24.portsmouth.uk.ibm.com (mk.ibm.com [9.149.105.60]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 16LEjsqO30540110 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 21 Jul 2021 14:45:54 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2899E42045; Wed, 21 Jul 2021 14:45:54 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1378C42042; Wed, 21 Jul 2021 14:45:53 +0000 (GMT) Received: from li-e979b1cc-23ba-11b2-a85c-dfd230f6cf82 (unknown [9.171.34.151]) by d06av24.portsmouth.uk.ibm.com (Postfix) with SMTP; Wed, 21 Jul 2021 14:45:52 +0000 (GMT) Date: Wed, 21 Jul 2021 16:45:50 +0200 From: Halil Pasic To: Tony Krowiak Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, cohuck@redhat.com, pasic@linux.vnet.ibm.com, jjherne@linux.ibm.com, jgg@nvidia.com, alex.williamson@redhat.com, kwankhede@nvidia.com, david@redhat.com Subject: Re: [PATCH 2/2] s390/vfio-ap: replace open coded locks for VFIO_GROUP_NOTIFY_SET_KVM notification Message-ID: <20210721164550.5402fe1c.pasic@linux.ibm.com> In-Reply-To: <20210719193503.793910-3-akrowiak@linux.ibm.com> References: <20210719193503.793910-1-akrowiak@linux.ibm.com> <20210719193503.793910-3-akrowiak@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: tOr7mkqCo33hLxPXSEAClv6pfQtjgpgP X-Proofpoint-ORIG-GUID: F0wvlLJxm9y82zazex2Nac9ePluYyTaj X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-07-21_09:2021-07-21,2021-07-21 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 priorityscore=1501 mlxlogscore=999 mlxscore=0 suspectscore=0 lowpriorityscore=0 impostorscore=0 spamscore=0 adultscore=0 malwarescore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2107210084 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On Mon, 19 Jul 2021 15:35:03 -0400 Tony Krowiak wrote: > It was pointed out during an unrelated patch review that locks should not [..] > -static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) > +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev, > + struct kvm *kvm) > { > - /* > - * If the KVM pointer is in the process of being set, wait until the > - * process has completed. > - */ > - wait_event_cmd(matrix_mdev->wait_for_kvm, > - !matrix_mdev->kvm_busy, > - mutex_unlock(&matrix_dev->lock), > - mutex_lock(&matrix_dev->lock)); > - > - if (matrix_mdev->kvm) { We used to check if matrix_mdev->kvm is null, but ... > - matrix_mdev->kvm_busy = true; > - mutex_unlock(&matrix_dev->lock); > - > - if (matrix_mdev->kvm->arch.crypto.crycbd) { > - down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem); > - matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > - up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem); > - > - kvm_arch_crypto_clear_masks(matrix_mdev->kvm); > - } > + if (kvm->arch.crypto.crycbd) { ... now we just try to dereference it. And .. > + down_write(&kvm->arch.crypto.pqap_hook_rwsem); > + kvm->arch.crypto.pqap_hook = NULL; > + up_write(&kvm->arch.crypto.pqap_hook_rwsem); > > + mutex_lock(&kvm->lock); > mutex_lock(&matrix_dev->lock); > + > + kvm_arch_crypto_clear_masks(kvm); > vfio_ap_mdev_reset_queues(matrix_mdev->mdev); > - kvm_put_kvm(matrix_mdev->kvm); > + kvm_put_kvm(kvm); > matrix_mdev->kvm = NULL; > - matrix_mdev->kvm_busy = false; > - wake_up_all(&matrix_mdev->wait_for_kvm); > + > + mutex_unlock(&kvm->lock); > + mutex_unlock(&matrix_dev->lock); > } > } > [..] > @@ -1363,14 +1323,11 @@ static void vfio_ap_mdev_release(struct mdev_device *mdev) > { > struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev); > > - mutex_lock(&matrix_dev->lock); > - vfio_ap_mdev_unset_kvm(matrix_mdev); > - mutex_unlock(&matrix_dev->lock); > - .. before access to the matrix_mdev->kvm used to be protected by the matrix_dev->lock ... > vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY, > &matrix_mdev->iommu_notifier); > vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY, > &matrix_mdev->group_notifier); > + vfio_ap_mdev_unset_kvm(matrix_mdev, matrix_mdev->kvm); ... but it is not any more. BTW I don't think the code is guaranteed to fetch ->kvm just once. Can you please explain why can we get away with being more lax when dealing with matrix_mdev->kvm? Regards, Halil [..]