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Tue, 15 Dec 2020 18:10:21 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5383DA4069; Tue, 15 Dec 2020 18:10:21 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.18.42]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 15 Dec 2020 18:10:21 +0000 (GMT) Subject: Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated To: Halil Pasic , Tony Krowiak Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org, gregkh@linuxfoundation.org, sashal@kernel.org, cohuck@redhat.com, kwankhede@nvidia.com, pbonzini@redhat.com, alex.williamson@redhat.com, pasic@linux.vnet.ibm.com References: <20201214165617.28685-1-akrowiak@linux.ibm.com> <20201215115746.3552e873.pasic@linux.ibm.com> From: Christian Borntraeger Message-ID: <44ffb312-964a-95c3-d691-38221cee2c0a@de.ibm.com> Date: Tue, 15 Dec 2020 19:10:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201215115746.3552e873.pasic@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=2020-12-15_12:2020-12-15,2020-12-15 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 priorityscore=1501 phishscore=0 mlxscore=0 spamscore=0 lowpriorityscore=0 malwarescore=0 clxscore=1011 adultscore=0 bulkscore=0 mlxlogscore=999 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012150118 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 15.12.20 11:57, Halil Pasic wrote: > On Mon, 14 Dec 2020 11:56:17 -0500 > Tony Krowiak wrote: > >> The vfio_ap device driver registers a group notifier with VFIO when the >> file descriptor for a VFIO mediated device for a KVM guest is opened to >> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM >> event). When the KVM pointer is set, the vfio_ap driver takes the >> following actions: >> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state >> of the mediated device. >> 2. Calls the kvm_get_kvm() function to increment its reference counter. >> 3. Sets the function pointer to the function that handles interception of >> the instruction that enables/disables interrupt processing. >> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to >> the guest. >> >> In order to avoid memory leaks, when the notifier is called to receive >> notification that the KVM pointer has been set to NULL, the vfio_ap device >> driver should reverse the actions taken when the KVM pointer was set. >> >> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback") >> Signed-off-by: Tony Krowiak >> --- >> drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++--------- >> 1 file changed, 20 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c >> index e0bde8518745..cd22e85588e1 100644 >> --- a/drivers/s390/crypto/vfio_ap_ops.c >> +++ b/drivers/s390/crypto/vfio_ap_ops.c >> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, >> { >> struct ap_matrix_mdev *m; >> >> - mutex_lock(&matrix_dev->lock); >> - >> list_for_each_entry(m, &matrix_dev->mdev_list, node) { >> if ((m != matrix_mdev) && (m->kvm == kvm)) { >> mutex_unlock(&matrix_dev->lock); >> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, >> matrix_mdev->kvm = kvm; >> kvm_get_kvm(kvm); >> kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; >> - mutex_unlock(&matrix_dev->lock); >> >> return 0; >> } >> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, >> return NOTIFY_DONE; >> } >> >> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) >> +{ >> + kvm_arch_crypto_clear_masks(matrix_mdev->kvm); >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > > > This patch LGTM. The only concern I have with it is whether a > different cpu is guaranteed to observe the above assignment as > an atomic operation. I think we didn't finish this discussion > at v1, or did we? You mean just this assigment: >> + matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; should either have the old or the new value, but not halve zero halve old? Normally this should be ok (and I would consider this a compiler bug if this is split into 2 32 bit zeroes) But if you really want to be sure then we can use WRITE_ONCE. I think we take this via the s390 tree? I can add the WRITE_ONCE when applying?