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Thu, 19 Aug 2021 13:36:35 +0000 (GMT) Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BCD2613604F; Thu, 19 Aug 2021 13:36:34 +0000 (GMT) Received: from cpe-172-100-181-211.stny.res.rr.com (unknown [9.160.182.229]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Thu, 19 Aug 2021 13:36:34 +0000 (GMT) Subject: Re: [PATCH 1/2] s390/vfio-ap: r/w lock for PQAP interception handler function pointer To: Halil Pasic , Christian Borntraeger Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, 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 References: <20210719193503.793910-1-akrowiak@linux.ibm.com> <20210719193503.793910-2-akrowiak@linux.ibm.com> <1a9f15d7-0f4d-00a0-0a8b-f1c08aa52eeb@de.ibm.com> <20210819012532.0e9c443c.pasic@linux.ibm.com> From: Tony Krowiak Message-ID: <8df389f7-44aa-978e-84d8-96c625b0470b@linux.ibm.com> Date: Thu, 19 Aug 2021 09:36:34 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210819012532.0e9c443c.pasic@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-ORIG-GUID: dC_GBF5zJjjm9JojMCJ3wYXRm4HpLBBI X-Proofpoint-GUID: z9oeVDuXijct1ftp08dJErYeU0wxAZV_ X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-19_04:2021-08-17,2021-08-19 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 impostorscore=0 spamscore=0 bulkscore=0 adultscore=0 mlxlogscore=999 malwarescore=0 clxscore=1011 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108190079 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/18/21 7:25 PM, Halil Pasic wrote: > On Wed, 18 Aug 2021 19:03:33 +0200 > Christian Borntraeger wrote: > >> On 19.07.21 21:35, Tony Krowiak wrote: >>> The function pointer to the interception handler for the PQAP instruction >>> can get changed during the interception process. Let's add a >>> semaphore to struct kvm_s390_crypto to control read/write access to the >>> function pointer contained therein. >>> >>> The semaphore must be locked for write access by the vfio_ap device driver >>> when notified that the KVM pointer has been set or cleared. It must be >>> locked for read access by the interception framework when the PQAP >>> instruction is intercepted. >>> >>> Signed-off-by: Tony Krowiak >>> Reviewed-by: Jason Gunthorpe >>> --- >>> arch/s390/include/asm/kvm_host.h | 8 +++----- >>> arch/s390/kvm/kvm-s390.c | 1 + >>> arch/s390/kvm/priv.c | 10 ++++++---- >>> drivers/s390/crypto/vfio_ap_ops.c | 23 +++++++++++++++++------ >>> drivers/s390/crypto/vfio_ap_private.h | 2 +- >>> 5 files changed, 28 insertions(+), 16 deletions(-) >>> >>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h >>> index 9b4473f76e56..f18849d259e6 100644 >>> --- a/arch/s390/include/asm/kvm_host.h >>> +++ b/arch/s390/include/asm/kvm_host.h >>> @@ -798,14 +798,12 @@ struct kvm_s390_cpu_model { >>> unsigned short ibc; >>> }; >>> >>> -struct kvm_s390_module_hook { >>> - int (*hook)(struct kvm_vcpu *vcpu); >>> - struct module *owner; >>> -}; >>> +typedef int (*crypto_hook)(struct kvm_vcpu *vcpu); >>> >>> struct kvm_s390_crypto { >>> struct kvm_s390_crypto_cb *crycb; >>> - struct kvm_s390_module_hook *pqap_hook; >>> + struct rw_semaphore pqap_hook_rwsem; >>> + crypto_hook *pqap_hook; >>> __u32 crycbd; >>> __u8 aes_kw; >>> __u8 dea_kw; >>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>> index b655a7d82bf0..a08f242a9f27 100644 >>> --- a/arch/s390/kvm/kvm-s390.c >>> +++ b/arch/s390/kvm/kvm-s390.c >>> @@ -2630,6 +2630,7 @@ static void kvm_s390_crypto_init(struct kvm *kvm) >>> { >>> kvm->arch.crypto.crycb = &kvm->arch.sie_page2->crycb; >>> kvm_s390_set_crycb_format(kvm); >>> + init_rwsem(&kvm->arch.crypto.pqap_hook_rwsem); >>> >>> if (!test_kvm_facility(kvm, 76)) >>> return; >>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c >>> index 9928f785c677..6bed9406c1f3 100644 >>> --- a/arch/s390/kvm/priv.c >>> +++ b/arch/s390/kvm/priv.c >>> @@ -610,6 +610,7 @@ static int handle_io_inst(struct kvm_vcpu *vcpu) >>> static int handle_pqap(struct kvm_vcpu *vcpu) >>> { >>> struct ap_queue_status status = {}; >>> + crypto_hook pqap_hook; >>> unsigned long reg0; >>> int ret; >>> uint8_t fc; >>> @@ -657,15 +658,16 @@ static int handle_pqap(struct kvm_vcpu *vcpu) >>> * Verify that the hook callback is registered, lock the owner >>> * and call the hook. >>> */ >>> + down_read(&vcpu->kvm->arch.crypto.pqap_hook_rwsem); >>> if (vcpu->kvm->arch.crypto.pqap_hook) { <--- HERE >>> - if (!try_module_get(vcpu->kvm->arch.crypto.pqap_hook->owner)) >>> - return -EOPNOTSUPP; >>> - ret = vcpu->kvm->arch.crypto.pqap_hook->hook(vcpu); >>> - module_put(vcpu->kvm->arch.crypto.pqap_hook->owner); >>> + pqap_hook = *vcpu->kvm->arch.crypto.pqap_hook; >> Dont we have to check for NULL here? If not can you add a comment why? > I believe we did the necessary check on the line I just marked with > "<--- HERE". > > I find that "*" operator confusing in this context as it doesn't do > any good for us. I believe this situation is described in 6.5.3.2.4 of > the c11 standard. For convenience I will cite from the corresponding > draft: > "The unary * operator denotes indirection. If the operand points to a > function, the result is a function designator; if it points to an > object, the result is an lvalue designating the object. If the operand > has type ‘‘pointer to type’’, the result has type ‘‘type’’. If an > invalid value has been assigned to the pointer, the behavior of the > unary * operator is undefined." > > Frankly I also fail to see the benefit of introducing the local variable > named "pqap_hook", but back then I decided to not complain about style. The vcpu->kvm->arch.crypto.pqap_hook is a pointer to a function pointer. The actual function pointer is stored in matrix_mdev->pqap_hook, the reason being that the handle_pqap function in vfio_ap_ops.c retrieves the matrix_mdev via a container_of macro. The dereferencing of the vcpu->kvm->arch.crypto.pqap_hook into a local variable was to get the function pointer. There may have been a more stylish way of doing this, but the functionality is there. > > Regards, > Halil > >> >>> + ret = pqap_hook(vcpu); >> [...]