From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Krowiak Subject: Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback Date: Thu, 7 Jun 2018 12:30:07 -0400 Message-ID: <5f9c3f97-34e2-bf68-b8ca-ac9288ea5efa@linux.vnet.ibm.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: pmorel@linux.ibm.com, 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 06/07/2018 11:20 AM, Pierre Morel wrote: > 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. What is LDD? Are you talking about dependencies between the vfio_ap device driver and KVM? If so, see my arguments below. > > > Also I think that with a little data structure refactoring you can > avoid most of > the code in the arch/s390/kvm. How will structure refactoring help us avoid the code for updating the CRYCB in the guest's SIE state description. > > > 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. How is that easier than storing the kvm pointer inside of the mediated matrix device (i.e., struct ap_matrix_mdev) which also contains the struct kvm_ap_matrix? How does that allow us to avoid the code in arch/s390/kvm? We still need the code to update the CRYCB in the SIE block. I can obviously avoid placing that code in kvm-ap.c and move it to the driver, but I already explained my reasoning for keeping it in KVM. Let's face it, there is no way around the dependency between the vfio_ap device driver and KVM unless guest matrix configuration is managed solely by KVM through KVM interfaces. Why maintain a list of kvm_ap_matrix structures if we don't have to; it is stored with the mediated matrix device which is passed in to all of the vfio_ap driver callbacks. > > > Pierre > >> >>> >>> >>> Sorry for the noise. >>> >>> Regards, >>> >>> Pierre >>> >>> >> >