From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pierre Morel Subject: Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback Date: Thu, 7 Jun 2018 17:20:40 +0200 Message-ID: References: <1525705912-12815-1-git-send-email-akrowiak@linux.vnet.ibm.com> <1525705912-12815-12-git-send-email-akrowiak@linux.vnet.ibm.com> <98ea7ce2-2539-e2ff-4bb4-297e784d87bd@linux.ibm.com> <7bb480ac-5723-83ff-c797-53c1ab0458c1@linux.vnet.ibm.com> <93cd0f46-a410-51c8-00b9-810c1b3d3ae2@linux.ibm.com> <0f37dc39-7355-19e5-40c9-a02a1ea58c2d@linux.vnet.ibm.com> <736a1346-f81a-7f71-7d13-38729ff78e4f@linux.ibm.com> <8f68183d-8385-8025-1898-23cad604ae94@linux.vnet.ibm.com> <9e30c9b0-a04c-0c4e-9d3d-37e7a53a7f72@linux.ibm.com> Reply-To: pmorel@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Tony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: freude@de.ibm.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com, kwankhede@nvidia.com, bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com, alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com, alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com, thuth@redhat.com, pasic@linux.vnet.ibm.com, berrange@redhat.com, fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com List-ID: On 07/06/2018 15:54, Tony Krowiak wrote: > On 06/06/2018 01:40 PM, Pierre Morel wrote: >> On 06/06/2018 18:08, Pierre Morel wrote: >>> On 06/06/2018 16:28, Tony Krowiak wrote: >>>> On 06/05/2018 08:19 AM, Pierre Morel wrote: >>>>> On 30/05/2018 16:33, Tony Krowiak wrote: >>>>>> On 05/24/2018 05:08 AM, Pierre Morel wrote: >>>>>>> On 23/05/2018 16:45, Tony Krowiak wrote: >>>>>>>> On 05/16/2018 04:03 AM, Pierre Morel wrote: >>>>>>>>> On 07/05/2018 17:11, Tony Krowiak wrote: >>>>>>>>>> Implements the open callback on the mediated matrix device. >>>>>>>>>> The function registers a group notifier to receive notification >>>>>>>>>> of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified, >>>>>>>>>> the vfio_ap device driver will get access to the guest's >>>>>>>>>> kvm structure. With access to this structure the driver will: >>>>>>>>>> >>>>>>>>>> 1. Ensure that only one mediated device is opened for the guest >>>>>>> >>>>>>> You should explain why. >>>>>>> >>>>>>>>>> >>>>>>>>>> 2. Configure access to the AP devices for the guest. >>>>>>>>>> >>>>>>> ...snip... >>>>>>>>>> +void kvm_ap_refcount_inc(struct kvm *kvm) >>>>>>>>>> +{ >>>>>>>>>> + atomic_inc(&kvm->arch.crypto.aprefs); >>>>>>>>>> +} >>>>>>>>>> +EXPORT_SYMBOL(kvm_ap_refcount_inc); >>>>>>>>>> + >>>>>>>>>> +void kvm_ap_refcount_dec(struct kvm *kvm) >>>>>>>>>> +{ >>>>>>>>>> + atomic_dec(&kvm->arch.crypto.aprefs); >>>>>>>>>> +} >>>>>>>>>> +EXPORT_SYMBOL(kvm_ap_refcount_dec); >>>>>>>>> >>>>>>>>> Why are these functions inside kvm-ap ? >>>>>>>>> Will anyone use this outer of vfio-ap ? >>>>>>>> >>>>>>>> As I've stated before, I made the choice to contain all >>>>>>>> interfaces that >>>>>>>> access KVM in kvm-ap because I don't think it is appropriate >>>>>>>> for the device >>>>>>>> driver to have to have "knowledge" of the inner workings of >>>>>>>> KVM. Why does >>>>>>>> it matter whether any entity outside of the vfio_ap device >>>>>>>> driver calls >>>>>>>> these functions? I could ask a similar question if the >>>>>>>> interfaces were >>>>>>>> contained in vfio-ap; what if another device driver needs >>>>>>>> access to these >>>>>>>> interfaces? >>>>>>> >>>>>>> This is very driver specific and only used during initialization. >>>>>>> It is not a common property of the cryptographic interface. >>>>>>> >>>>>>> I really think you should handle this inside the driver. >>>>>> >>>>>> We are going to have to agree to disagree on this one. Is it not >>>>>> possible >>>>>> that future drivers - e.g., when full virtualization is >>>>>> implemented - will >>>>>> require access to KVM? >>>>> >>>>> I do not think that an access to KVM is required for full >>>>> virtualization. >>>> >>>> You may be right, but at this point, there is no guarantee. I stand >>>> by my >>>> design on this one. >>> >>> I really regret that we abandoned the initial design with the matrix >>> bus and one >>> single parent matrix device per guest. >>> We would not have the problem of these KVM dependencies. >>> >>> It had the advantage of taking care of having only one device per guest >>> (available_instance = 1), could take care of provisioning as you have >>> sysfs entries available for a matrix without having a guest and a >>> mediated >>> device. >>> >>> it also had advantage for virtualization to keep host side and guest >>> side matrix >>> separate inside parent (host side) and mediated device (guest side). >>> >>> Shouldn't we treat this problem with a design using standard interfaces >>> Instead of adding new dedicated interfaces? >>> >>> Regards, >>> >>> Pierre >>> >>> >> >> Forget it. >> >> I am not happy with the design but the design I was speaking of may >> not be the solution either. > > The AP architecture makes virtualization of AP devices complex. We > tried the solution you > described and found it to be sorely lacking which is why we ended up > where we are now. I did not see any explanation on why between v1 and v2 as it was abandoned. We have internal structures like the ap_matrix and kvm_ap_matrix which look like the bus/devices we had previously but are differently or not at all integrated with the LDD. Also I think that with a little data structure refactoring you can avoid most of the code in the arch/s390/kvm. For example, storing the kvm pointer inside the kvm_ap_matrix and maintaining a list of the kvm_ap_matrix structures allows to easily know if a guest already has an associated mediated device. Pierre > >> >> >> Sorry for the noise. >> >> Regards, >> >> Pierre >> >> > -- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany