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Tue, 25 May 2021 13:16:31 +0000 (GMT) Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AF75F136053; Tue, 25 May 2021 13:16:30 +0000 (GMT) Received: from cpe-172-100-179-72.stny.res.rr.com (unknown [9.85.177.219]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Tue, 25 May 2021 13:16:30 +0000 (GMT) Subject: Re: [PATCH v4 2/2] s390/vfio-ap: control access to PQAP(AQIC) interception handler To: jjherne@linux.ibm.com, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Cc: borntraeger@de.ibm.com, cohuck@redhat.com, pasic@linux.vnet.ibm.com, jgg@nvidia.com, alex.williamson@redhat.com, kwankhede@nvidia.com, frankja@linux.ibm.com, david@redhat.com, imbrenda@linux.ibm.com, hca@linux.ibm.com References: <20210521193648.940864-1-akrowiak@linux.ibm.com> <20210521193648.940864-3-akrowiak@linux.ibm.com> <5d15fdf2-aee8-4e6c-c3e1-f07c76ce5974@linux.ibm.com> From: Tony Krowiak Message-ID: Date: Tue, 25 May 2021 09:16:30 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <5d15fdf2-aee8-4e6c-c3e1-f07c76ce5974@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 1LsBpQtMWwXf_3q_6G8F4ikH0DPQJZPk X-Proofpoint-ORIG-GUID: hpRYyVtOsdTXCrFB4M7UiD-1mZbdeWei X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-05-25_06:2021-05-25,2021-05-25 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 impostorscore=0 clxscore=1015 phishscore=0 mlxlogscore=999 adultscore=0 lowpriorityscore=0 bulkscore=0 suspectscore=0 mlxscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2105250081 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/24/21 10:37 AM, Jason J. Herne wrote: > On 5/21/21 3:36 PM, Tony Krowiak wrote: >> The function pointer to the handler that processes interception of the >> PQAP instruction is contained in the mdev. If the mdev is removed and >> its storage de-allocated during the processing of the PQAP instruction, >> the function pointer could get wiped out before the function is called >> because there is currently nothing that controls access to it. >> >> This patch introduces two new functions: >> * The kvm_arch_crypto_register_hook() function registers a function >> pointer >>    for processing intercepted crypto instructions. >> * The kvm_arch_crypto_register_hook() function un-registers a function >>    pointer that was previously registered. > > Typo: You meant kvm_arch_crypto_UNregister_hook() in the second bullet. > > > Just one overall observation on this one. The whole hook system seems > kind of over-engineered if this is our only use for it. It looks like > a kvm_s390_crypto_hook is meant to link a specific module with a > function pointer. Do we really need this concept? > > I think a simpler design could be to just place a mutex and a function > pointer in the kvm_s390_crypto struct. Then you can grab the mutex in > vfio_ap_ops.c when registering/unregistering. You would also grab the > mutex in priv.c when calling the function pointer. What I am > suggesting is essentially the exact same scheme you have implemented > here, but simpler and with less infrastructure. That would be great, however; when I implemented something similar, it resulted in a lockdep splat between the lock used to protect the hook and the matrix_dev->lock used to protect updates to matrix_mdev (including the freeing thereof). After pulling what little hair I have left out, this seemed like a reasonable solution, over-engineered though it may be. If somebody has a simpler solution, I'm all ears. > > With that said, I'll point out that I am relative new to this code > (and this patch series) so maybe I've missed something and the extra > complexity is needed for some reason. But if it is not, I'm all in > favor of keeping things simple. >