Messages in this thread | | | Subject | Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback | From | Pierre Morel <> | Date | Thu, 7 Jun 2018 17:20:40 +0200 |
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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
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