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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 E8FB7C43381 for ; Tue, 19 Mar 2019 14:23:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B2D342133D for ; Tue, 19 Mar 2019 14:23:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727270AbfCSOXZ (ORCPT ); Tue, 19 Mar 2019 10:23:25 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:52518 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726661AbfCSOXY (ORCPT ); Tue, 19 Mar 2019 10:23:24 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x2JEEqh4093450 for ; Tue, 19 Mar 2019 10:23:23 -0400 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rb0g3df9a-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 19 Mar 2019 10:23:23 -0400 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 19 Mar 2019 14:23:15 -0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x2JENEEW59048176 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 19 Mar 2019 14:23:14 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 78C7DAE051; Tue, 19 Mar 2019 14:23:14 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C8C37AE04D; Tue, 19 Mar 2019 14:23:13 +0000 (GMT) Received: from [9.145.41.62] (unknown [9.145.41.62]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 19 Mar 2019 14:23:13 +0000 (GMT) Reply-To: pmorel@linux.ibm.com Subject: Re: [PATCH v5 4/7] s390: ap: setup relation betwen KVM and mediated device To: Halil Pasic Cc: borntraeger@de.ibm.com, alex.williamson@redhat.com, cohuck@redhat.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, frankja@linux.ibm.com, akrowiak@linux.ibm.com, david@redhat.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, freude@linux.ibm.com, mimu@linux.ibm.com References: <1552493104-30510-1-git-send-email-pmorel@linux.ibm.com> <1552493104-30510-5-git-send-email-pmorel@linux.ibm.com> <20190315191557.6c8d7668@oc2783563651> <7c199329-0e82-ff61-46b7-78237a0f01ce@linux.ibm.com> <20190319125425.0cf5324e@oc2783563651> From: Pierre Morel Date: Tue, 19 Mar 2019 15:23:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190319125425.0cf5324e@oc2783563651> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19031914-0028-0000-0000-00000355E459 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19031914-0029-0000-0000-000024148218 Message-Id: <2c459ebe-2b37-72bc-1ede-b196e54dc78d@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-19_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903190106 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/03/2019 12:54, Halil Pasic wrote: > On Tue, 19 Mar 2019 10:38:42 +0100 > Pierre Morel wrote: > >> On 15/03/2019 19:15, Halil Pasic wrote: >>> On Wed, 13 Mar 2019 17:05:01 +0100 >>> Pierre Morel wrote: >>> >>>> When the mediated device is open we setup the relation with KVM unset it >>>> when the mediated device is released. >>>> >>>> We ensure KVM is present on opening of the mediated device. >>>> >>>> We ensure that KVM survives the mediated device, and establish a direct >>> >>> survives? >> >> what alternative do you prefer? >> > > Increase kvm's refcount to ensure the guest is alive when the > ap_matrix_mdev is active. An ap mp_matrix becomes active with > a successful open() and ceases to be active with a release(). Right, it is mdev usage not mdev. > > Your sentence was materially wrong as the mdev is allowed to outlive > the KVM. BTW survive tends to have an 'in spite of' note to it, which > outlive does not. vfio-ap is, I hope, not a calamity that threatens > the life of KVM ;). https://en.oxforddictionaries.com/definition/survive Thanks, your description is much better. > >>> >>>> link from KVM to the mediated device to simplify the relationship. >>>> >>>> Signed-off-by: Pierre Morel >>>> --- >> >> ...snip... >> >>>> static int vfio_ap_mdev_group_notifier(struct notifier_block *nb, >>>> unsigned long action, void *data) >>>> { >>>> - int ret; >>>> struct ap_matrix_mdev *matrix_mdev; >>>> >>>> if (action != VFIO_GROUP_NOTIFY_SET_KVM) >>>> return NOTIFY_OK; >>>> >>>> matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier); >>>> - >>>> - if (!data) { >>>> - matrix_mdev->kvm = NULL; >>>> - return NOTIFY_OK; >>>> - } >>>> - >>>> - ret = vfio_ap_mdev_set_kvm(matrix_mdev, data); >>>> - if (ret) >>>> - return NOTIFY_DONE; >>>> - >>>> - /* If there is no CRYCB pointer, then we can't copy the masks */ >>>> - if (!matrix_mdev->kvm->arch.crypto.crycbd) >>>> - return NOTIFY_DONE; >>>> - >>>> - kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm, >>>> - matrix_mdev->matrix.aqm, >>>> - matrix_mdev->matrix.adm); >>>> + matrix_mdev->kvm = data; >>>> >>>> return NOTIFY_OK; >>>> } >>>> @@ -888,6 +873,12 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev) >>>> if (ret) >>>> goto err_group; >>>> >>>> + /* We do not support opening the mediated device without KVM */ >>>> + if (!matrix_mdev->kvm) { >>>> + ret = -ENODEV; >>>> + goto err_group; >>>> + } >>>> + >>>> matrix_mdev->iommu_notifier.notifier_call = vfio_ap_mdev_iommu_notifier; >>>> events = VFIO_IOMMU_NOTIFY_DMA_UNMAP; >>>> >>>> @@ -896,8 +887,15 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev) >>>> if (ret) >>>> goto err_iommu; >>>> >>>> + ret = vfio_ap_mdev_set_kvm(matrix_mdev); >>> >>> At this point the matrix_mdev->kvm ain't guaranteed to be valid IMHO. Or >>> am I wrong? If I'm right kvm_get_kvm(matrix_mdev->kvm) could be too late. >> >> What about the if (!matrix_mdev->kvm) 10 lines above ? >> > > That check is not sufficient. > > You should do the kvm_get_kvm() in vfio_ap_mdev_group_notifier(). VFIO > must ensure that the kvm pointer you get is valid, in a sense that it > points to a valid struct kvm and the kvm object is alive, while you are > in the callback. But not beyond. > > If another thread were to decrement the refcount of the kvm object you > would end up with matrix_mdev->kvm pointing to an object that has already > died. > > Does my analysis make sense to you? Yes thanks the explication is good, it would have been worth to get it the first time. > >>> >>>> + if (ret) >>>> + goto err_kvm; >>>> + >>>> return 0; >>>> >>>> +err_kvm: >>>> + vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY, >>>> + &matrix_mdev->iommu_notifier); >>>> err_iommu: >>>> vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY, >>>> &matrix_mdev->group_notifier); >>>> @@ -906,19 +904,33 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev) >>>> return ret; >>>> } >>>> >>>> -static void vfio_ap_mdev_release(struct mdev_device *mdev) >>>> +static int vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) >>>> { >>>> - struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev); >>>> + struct kvm *kvm = matrix_mdev->kvm; >>>> >>>> if (matrix_mdev->kvm) >>>> kvm_arch_crypto_clear_masks(matrix_mdev->kvm); >>> >>> This still conditional? >> >> Yes, nothing to clear if there is no KVM. >> > > Since we have ensured the open only works if there is a KVM at that > point in time, and we have taken a reference to KVM, I would expect > KVM can not go away before we give up our reference. Right. Thanks, Pierre -- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany